Abstract
Fossil fuel-based products should be replaced by products derived from modern biomass such as plant starch, in the context of the future circular economy. Starch production globally surpasses 50 million tons annually, predominantly sourced from maize, rice, and potatoes. Here, we review plant starch with an emphasis on structure and properties, extraction, modification, and green applications. Modification techniques comprise physical, enzymatic, and genetic methods. Applications include stabilization of food, replacement of meat, three-dimensional food printing, prebiotics, encapsulation, bioplastics, edible films, textiles, and wood adhesives. Starch from maize, potatoes, and cassava shows amylose content ranging from 20 to 30% in regular varieties to 70% in high-amylose varieties. Extraction by traditional wet milling achieves starch purity up to 99.5%, while enzymatic methods maintain higher structural integrity, which is crucial for pharmaceutical applications. Enzymatic extraction improves starch yield by of up to 20%, reduces energy consumption by about 30%, and lowers wastewater production by up to 50%, compared to conventional methods. Sustainable starch modification can reduce the carbon footprint of starch production by up to 40%. Modified starches contribute to approximately 70% of the food texturizers market. The market of starch in plant-based meat alternatives has grown by over 30% in the past five years. Similarly, the use of biodegradable starch-based plastics by the bioplastic industry is growing over 20% annually, driven by the demand for sustainable packaging.Kindly check and confirm the layout of Table 1.Layout is right
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Introduction
Polysaccharides are non-toxic functional biological macromolecules produced naturally in plants, animals, marine algae, and microorganisms, where plants polysaccharides such as cellulose, starch, plant gums, and pectin, animals’ polysaccharides including chitin, chitosan, and hyaluronic acid, marine algae polysaccharides such as alginate, agar, and carrageenan, and microorganisms polysaccharides including dextran and gellan gum. Recently, their noteworthy attributes, such as renewability, biodegradability, and biocompatibility, have positioned them as a valuable resource in various studies (Bo et al. 2024; Huang et al. 2022; Janik et al. 2024; Liu et al. 2024a; Sohouli et al. 2022). Among these sources of polysaccharides, plants are regarded as optimal sources due to their widespread availability, cost-effectiveness, and the simplicity of their extraction process. Furthermore, plant polysaccharides, especially starch, can be used in diverse industries, including food and pharmaceuticals, because of their low side effects (Chang et al. 2022; Li et al. 2024; Seidi et al. 2022; Zhao et al. 2024). Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units connected by glycosidic bonds, which serves as a primary energy storage molecule in plants and a significant dietary source for humans, contributing to nutritional sustenance (Kaplan et al. 2019; Rong et al. 2023; Zhang et al. 2024b). Primary starch origins encompass grains such as maize, wheat, rice, sorghum, and barley; tubers including potato, sweet potato, cassava, and yam; and unripe fruits including banana and plantain. Starch serves as a ubiquitous polymer extensively employed in food processing due to its versatility (Chen et al. 2024; Park and Kim 2021; Zhao et al. 2018; Zou et al. 2020).
Starch's widespread use is attributed not only to its cost-effectiveness and ample availability but also to the ability to tailor its physicochemical characteristics through various methods, including physical, chemical, enzymatic, and other techniques to yield modified starch with desired properties (Chen et al. 2024; Park and Kim 2021; Zhao et al. 2018; Zou et al. 2020). Starch-based materials find extensive application across diverse industries including food, paper, textile, plastic, cosmetics, adhesives, and pharmaceuticals. As a primary source of dietary carbohydrates, starchy foods contribute significantly to human calorie intake, representing approximately 80% of the global average (Gerrano et al. 2014; Liu et al. 2017; Marta et al. 2022). Nonetheless, native starch derived from plants often lacks resilience to harsh processing conditions such as elevated temperatures, freeze–thaw cycles, exposure to strong acids and alkalis, and high shear rates (Bühler et al. 2022; Liu et al. 2017). Hence, its utilization is constrained, rendering it unsuitable for numerous industrial uses; therefore, various methods are employed to modify native starch, aiming to enhance or suppress its intrinsic attributes or confer specific properties to align with industrial needs. Prominent modes of modification encompass physical techniques such as high-pressure autoclave treatment, osmotic pressure treatment, and extrusion, chemical approaches including oxidation, esterification, etherification, and hydroxypropylation, and enzymatic modifications such as dextrinization (Fig. 1) (Li et al. 2024; Punia Bangar et al. 2022; Rashwan et al. 2023a; Zhao et al. 2024).
Common plant sources, modification technologies, and potential application of starch. Cereal-based starch, including maize starch, rice starch, wheat starch, barley starch, and sorghum starch. Tuber-based starch such as potato starch, sweet potato starch, and yam starch. The common root-based starch is cassava starch and taro starch, and green banana starch is an example of fruit-based starch. Starch modification techniques such as physical, chemical, and enzymatic modification treatments. Physical modification techniques such as high-pressure autoclave treatment, osmotic pressure treatment, and extrusion. Chemical modification approaches include oxidation, esterification, etherification, and hydroxypropylation, as well as enzymatic modifications such as dextrinization. Potential starch applications such as food stabilizers, three-dimensional food printing, prebiotic nutrients, synthesis encapsulation systems, food additives in plant-based meat, and bioplastics and edible coatings
Therefore, the novelty and progress of the current review lie in its discussion of the physicochemical and functional attributes of starch derived from plants. Additionally, it provided an overview of starch-rich plant sources, discussed potential methods for extracting and modifying starch, and outlined potential applications of plant-based starch in the development of food and related products. As a result, this review presents a valuable contribution regarding starch-rich plants and their derivatives, potentially garnering interest from both food researchers and industrial stakeholders.
Starch-rich plants
Starch-rich plant sources are integral to diets worldwide, providing essential carbohydrates and energy to millions of people. These plants serve as staples in various cuisines, contributing to both nutrition and culinary diversity (Boahemaa et al. 2024). Starch serves as a vital nutritional and energy source for humans and animals. Furthermore, it finds widespread usage in various non-food industrial sectors for diverse applications (Apriyanto et al. 2022; Yao et al. 2021). Starch, a flavorless and scentless powder, stands as one of the most prevalent natural polysaccharides derived from plants, with global production exceeding 50 million tons annually (Cheng et al. 2021; Jiang et al. 2020). Table 1 shows the most common source to produce starch worldwide.
Maize, also known as corn, is one of the most widely cultivated cereal crops globally. It is a staple food in many countries, particularly in regions including North and South America, Africa, and Asia. The quantity of starch in maize (corn) seeds can vary depending on factors such as the variety of maize, growing conditions, and maturity at harvest. However, maize seeds typically contain a significant amount of starch, as starch serves as the primary energy storage molecule in seeds. On average, maize seeds can contain around 60–75% starch by dry weight. This high starch content makes maize an important crop not only for human consumption but also for various industrial purposes, such as the production of cornstarch, corn syrup, and ethanol. The starch content in maize seeds makes it a valuable source of carbohydrates in human and animal diets, and it is used in a wide range of food products, including cornmeal, cornflakes, and tortillas, among others. Additionally, maize starch is utilized in non-food applications such as in the production of biodegradable plastics, adhesives, and textiles (Chen et al. 2021a; Huang et al. 2024; Kaplan et al. 2019; Liu et al. 2024b).
Rice is another staple cereal crop consumed by a significant portion of the world's population, particularly in Asia. It is rich in starch, providing a readily available source of energy. The quantity of starch in rice seeds also varies depending on factors, including the rice variety, growing conditions, and maturity at harvest. Rice, like maize, serves as a major source of carbohydrates in many diets worldwide. Different varieties of rice, such as long grain, medium grain, and short grain, are used in diverse culinary preparations, including rice-based dishes, bread, noodles, yogurt, and desserts (Tiozon et al. 2021; You et al. 2024). The starch content in rice seeds is typically around 70–80% dry weight, and this high starch content makes rice a staple food for a large portion of the global population. The starch in rice seeds provides a readily available source of energy, making rice an important component of diets in many cultures. Like maize, rice starch is also utilized in various food and non-food applications. In food, rice starch is used in products such as rice flour, rice noodles, and rice cakes. In non-food applications, rice starch finds use in industries such as pharmaceuticals, cosmetics, and textiles (Dhital et al. 2015; Krishnan et al. 2020; Obadi et al. 2023; Zhu et al. 2023).
Wheat is one of the oldest cultivated grains and a staple food in many parts of the world. It contains a substantial amount of starch, making it an important source of carbohydrates. On average, wheat grains can contain around 60–75% starch by dry weight. This high starch content makes wheat a valuable staple crop for human consumption and a key ingredient in various food products worldwide. Wheat starch is utilized in a wide range of food applications, including baking, pasta production, and the manufacturing of breakfast cereals, snacks, and confectionery items. Additionally, wheat starch is used in non-food industries such as papermaking, textiles, and pharmaceuticals (Baranzelli et al. 2019; Ee et al. 2020; Maniglia et al. 2020).
Furthermore, sorghum grains contain a significant amount of starch, like other cereal grains, where it contains around 60–75% starch by dry weight, and this starch content makes sorghum an important staple crop for human consumption and a valuable feedstock for various industrial applications. Sorghum starch has several uses, including food and non-food applications. In food, sorghum starch is used in products such as sorghum flour, breakfast cereals, baked goods, and beverages. Sorghum is also a key ingredient in gluten-free products, providing an alternative for individuals with gluten intolerance or celiac disease. In non-food applications, sorghum starch finds use in industries such as papermaking, textiles, adhesives, and biofuel production. The versatility of sorghum starch makes it a valuable commodity in both agricultural and industrial sectors (Cruz et al. 2015; Gerrano et al. 2014; Sorour et al. 2019; Yan et al. 2023).
Cassava, a key crop in tropical regions, is renowned for its high starch content, serving as a crucial carbohydrate source globally. Cassava roots typically contain 60% to 80% starch by dry weight, ranking it among the richest starch sources in root crops. Predominantly composed of amylopectin, a branched polysaccharide, cassava starch contributes to its distinct culinary and industrial qualities. Its abundant starch makes cassava indispensable in various food items such as flour, starch, and tapioca pearls. Despite its low protein content, cassava provides essential nutrients such as fiber, vitamins, and minerals, making it significant in local diets. Furthermore, cassava starch finds applications in industries, including biofuel, adhesive, and biodegradable plastic production, as well as in food processing as a thickener, stabilizer, and texturizer. However, cassava contains toxic compounds, including cyanogenic glycosides, necessitating proper processing to eliminate cyanide. Failure to do so poses health risks, underscoring the importance of adhering to safe preparation methods (Akonor et al. 2023; Jumaidin et al. 2020; Moura et al. 2021; Tappiban et al. 2020; Xie et al. 2013; Zou et al. 2023).
Additionally, the starch content in potato tubers can vary depending on factors such as the potato variety, growing conditions, and storage conditions. Potatoes are known for their relatively high starch content compared to other tubers, which contain around 15–20% starch by fresh weight. However, this can vary significantly depending on the specific variety of potato and its stage of maturity. Starch content tends to increase as potatoes mature and reach full size. Starch serves as the primary carbohydrate reserve in potato tubers, providing energy for the plant during growth and serving as a storage compound for nutrients. Starch also contributes to the texture and culinary properties of potatoes, influencing characteristics such as texture, taste, and cooking behavior. Potatoes are a versatile crop with numerous culinary applications, and their starch content plays a significant role in their uses. Potatoes can be boiled, mashed, fried, roasted, or baked, and their starch content affects the final texture and consistency of the prepared dish (Juarez-Arellano et al. 2021; Reyniers et al. 2020; Yang et al. 2022b).
Sweet potatoes are known for their distinct flavor and nutritional benefits, and their starch content contributes to these characteristics. They are particularly popular in cuisines across Asia, Africa, and the Americas. On average, sweet potatoes have around 10–20% starch by fresh weight; however, the starch content in sweet potatoes can fluctuate depending on factors such as the specific variety and growing conditions. Generally, younger sweet potatoes tend to have a lower starch content, while more mature sweet potatoes may have higher levels of starch. Despite their name, sweet potatoes are not as high in starch as other starchy vegetables like regular potatoes. Instead, sweet potatoes are known for their high content of complex carbohydrates, fiber, vitamins, and minerals. The starch in sweet potatoes contributes to their texture and can affect cooking methods and outcomes. Due to their versatility and nutritional value, sweet potatoes are used in a variety of culinary applications, including roasting, baking, boiling, and mashing. The starch content of sweet potatoes influences their texture and sweetness, making them suitable for both savory and sweet dishes (Aina et al. 2012; Al-Maqtari et al. 2024; Cavalcanti et al. 2019; Ghoshal and Kaur 2023; Kale et al. 2017; Song et al. 2021; Wang et al. 2020b).
Taro is a tropical root vegetable with a starchy corm that is widely consumed in Asia, Africa, the Pacific Islands, and the Caribbean. Taro possesses variable starch levels influenced by factors like variety, growth conditions, and maturity. Besides, taro boasts a substantial starch content that ranges from 60 to 90% by dry weight, where this significant concentration of starch enhances its nutritional profile and adaptability in cooking. Despite its starch richness, taro also offers a spectrum of essential nutrients such as dietary fiber, vitamins, and minerals, augmenting its value in balanced diets. Culinary-wise, taro's starch content accommodates diverse cooking techniques such as boiling, steaming, frying, or mashing, facilitating its integration into a wide array of global cuisines due to its creamy consistency and thickening properties for sauces and soups. Furthermore, beyond its culinary utility, taro's abundant starch finds application in industries like the production of biodegradable packaging, adhesives, and textiles, owing to its adhesive nature and eco-friendliness. Despite its nutritional and functional merits, individuals with specific dietary concerns, particularly those managing carbohydrate intake, should be cautious about taro's high starch content (Shanmathy et al. 2021; Singla et al. 2020; Zhang and Huang 2022).
Plantains, a starchy fruit closely related to bananas, contain varying amounts of starch depending on factors such as ripeness and variety. When unripe, plantains have a higher starch content, typically ranging from 70 to 80% by dry weight, making them more suitable for cooking methods such as frying, boiling, or baking. As plantains ripen, their starch content decreases, and their sugar content increases, leading to sweeter flavors and softer textures. Ripe plantains contain less starch, usually around 20% to 30%, with a higher sugar content. This change in composition affects the culinary applications of plantains, with ripe plantains commonly used in sweet dishes, including desserts or fried as a snack. However, both ripe and unripe plantains offer nutritional benefits, including dietary fiber, vitamins, and minerals, making them a valuable addition to diets in many cultures (Marta et al. 2022; Vega-Rojas et al. 2021; Viana et al. 2022).
To summarize, these starch-rich plant sources play crucial roles in global food security, providing sustenance and nourishment to diverse populations. They are valued not only for their nutritional content but also for their cultural significance and culinary versatility. Incorporating these plant-based staples into diets helps ensure contribute intake of essential nutrients and contributes to the promotion of sustainable and healthy eating habits.
Structure
The structure of starch is composed of two main components, amylose and amylopectin, shown in Fig. 2 (Boahemaa et al. 2024; Vamadevan and Bertoft 2020).
Starch is a complex carbohydrate consisting of glucose units bonded together in long chains. The structure of starch, including amylose and amylopectin polymers. Amylose is a type of starch molecule characterized by its linear structure, consisting of long chains of glucose units linked together by alpha (α)-1,4-glycosidic bonds. Amylopectin is a branched-chain polymer and a major component of starch, characterized by its highly branched structure. Amylopectin consists of linear chains of glucose units linked by α-1,4-glycosidic bonds, with occasional α-1,6-glycosidic bonds forming branches
Amylose is a linear polymer of glucose molecules linked by α-1,4-glycosidic bonds, forming a helical structure. Amylose constitutes about 20–30% of starch molecules. The linear structure of amylose allows it to form helical coils, which contribute to the thickening and gelling properties of starch when heated in the presence of water (Obadi et al. 2023). On the other hand, amylopectin makes up most starch molecules, around 70–80%, which is a branched polymer with both α-1,4- and α-1,6-glycosidic bonds. This branching creates a more complex, treelike structure compared to amylose. Besides, the branched structure of amylopectin allows for more extensive branching and contributes to the viscosity and texture of starch solutions (Chen et al. 2021a; Li et al. 2020a). Starch molecules form granules, which vary in size and shape depending on the botanical source and processing methods. These granules contain both amylose and amylopectin, arranged in a semicrystalline matrix. The structure of starch granules influences their functionality in various applications, such as food and industrial processes (Chen et al. 2021a; Li et al. 2020a).
Besides, the chemical composition and structural characteristics of starches vary not only among different sources but also within each type of starch. These variations encompass factors such as the presence of α-glucans, moisture content, lipid composition, protein content, and levels of phosphorylated residues. These attributes influence the surface properties and hardness of starch granules (Cao et al. 2019; Chang et al. 2022; Oh et al. 2020). Amylose plays a pivotal role in organizing amylopectin into crystalline structures and arranging crystalline layers within starch granules. This arrangement significantly affects properties related to water absorption, such as swelling and gelatinization. Moreover, the variability in amylose content within starches sourced from the same botanical origin impacts granule size distribution, molecular characteristics of amylose and amylopectin, and functional attributes such as paste temperature and viscosity. The distribution of amylopectin chain lengths, which varies across botanical sources, is another critical determinant of starch properties. Short amylopectin chains with extensive branching promote the formation of amylose–lipid helical complexes. Starches with elevated amylose content exhibit heightened exothermicity and can form more stable amylose–lipid complexes, influencing thermal behaviors and gel formation (Cornejo-Ramírez et al. 2018; Cruz et al. 2015; Li et al. 2024; Liu et al. 2017; Zavareze and Dias 2011).
To summarize, amylose and amylopectin are the two primary components of starch, each contributing unique properties. Amylose, a linear polymer, makes up about 20–30% of starch and forms helical structures that aid in thickening and gelling when heated with water. In contrast, amylopectin accounts for 70–80% of starch and has a branched structure that enhances the viscosity and texture of starch solutions. These components are organized within starch granules that vary in shape and size based on their source and processing. The variations in starch composition, including differences in moisture, lipids, and proteins, influence the functionality of starch in applications ranging from food to industrial processes. The structural characteristics of starch granules, particularly the arrangement of amylose and amylopectin, significantly affect their water absorption properties, thermal behaviors, and gel formation.
Properties
Starch, a natural biopolymer predominantly found in plants, is used in various industries due to its unique physicochemical and functional properties. Physiochemically, starch is composed of two types of molecules: amylose, a linear polymer, and amylopectin, a highly branched polymer (Fig. 2). These components affect key properties such as granule size, shape (Fig. 3), gelatinization temperature, and solubility, which vary according to the botanical source (Boahemaa et al. 2024; Chen et al. 2024; Zhang et al. 2024b).
Granular shape of starch from most common sources, visualized using microscopic imaging. Maize starch granules are described as having round and polygonal shapes, while potato starch granules are oval and spherical. Rice starch with round, angular, and polygonal shapes, and cassava starch is characterized by round, irregular shapes. The images provide a visual comparison across different starch sources such as sorghum, wheat, taro, yam, banana, barley, and sweet potato, each with distinct granular shapes. This layout not only highlights the diversity in starch granule morphology but also serves as an educational tool for understanding the physical characteristics of starches derived from different plants. These images with Copyright permissions, 2024, Elsevier, John Wiley and Sons, and Springer Nature (Abegunde et al. 2013; Agama-Acevedo et al. 2011; Baranzelli et al. 2019; Cai et al. 2014; Kumar et al. 2020; You et al. 2024; Liu et al. 2016; Park et al. 2024a; Shao et al. 2020; Yang et al. 2022a; Yulianto et al. 2020)
Starches derived from various plant sources frequently exhibit variations in their composition and structural attributes, leading to differences in their physicochemical properties, such as thermal behavior, rheology, solubility, swelling, hydrolysis, and degradation. These differences are fundamental to the development and manufacturing of starch-based products. Additionally, the functional properties of starch granules, such as swelling power, solubility, gelatinization, retrogradation, syneresis, and rheological behavior, are typically governed by the diverse characteristics of the starch structure (Table 2) (Hou et al. 2023; Liu et al. 2024b; Obadi et al. 2023; Thanyapanich et al. 2021; Wang et al. 2020b; Yan et al. 2023; Yang et al. 2022a). For example, the study investigated barley starch and its blends with corn, wheat, and rice starches. Amylose content varied significantly, ranging from 10.9% in rice to 41.4% in barley starch. Barley starch granules were the largest, with others showing varied sizes and shapes. Gelatinization temperatures and enthalpies differed among the starches, with corn and rice starches generally showing higher transition temperatures. Pasting and rheological properties were influenced by amylose content, with higher-amylose blends showing greater resistance to swelling and lower peak viscosity. Retrogradation was more pronounced in barley starch, indicating a higher tendency toward recrystallization compared to other starches (Gupta et al. 2009).
Furthermore, Aina et al. (2012) assessed the physicochemical properties of starches from 21 Caribbean sweet potato cultivars, revealing significant variability. They found that moisture content ranged from 8.0 to 12.4%, protein was between 0.0 and 0.2%, ash varied from 0.1 to 0.5%, and reducing sugars from 0.3 to 2.3%. Amylose content spanned from 12.8% to 21.3%. Swelling power was observed between 7.8 and 31.1%, while solubility ranged from 1.5 to 9.6%. Pasting properties showed a wide range of peak viscosities from 143.2 to 288.8 Rapid Visco Units, with corresponding pasting temperatures between 73.5 and 87.7 °C. The study underscores the diversity in starch properties, which is important for their specific food application potentials (Aina et al. 2012). Another study found that wheat starch properties varied with the ratio of A and B granules. A granules, larger in size, showed higher gelatinization temperatures, where the conclusion temperature was 80.28 °C and enthalpy was 3.268 Joules per gram.
In contrast, smaller B granules had higher peak temperatures was 66.00 °C and lower enthalpy was 2.237 Joules per gram. As the ratio of B granules increased, mixed starches displayed higher gelatinization onset, peak, and conclusion temperatures while their enthalpy and viscosity parameters decreased, indicating a correlation between granule composition and starch functionality (Zeng et al. 2014). The granular shape of sorghum starch varies depending on the botanical source and processing methods. Sorghum starch granules are irregular in shape, ranging from oval to spherical. They can also exhibit facets or irregular surfaces. The size of the granules may vary, with some being relatively large compared to other starch sources. Additionally, sorghum starch granules may have a smooth or rough texture, depending on factors such as genetic variation and processing conditions (Sorour et al. 2019).
Additionally, the study by Guo et al. (2019) assessed starch properties from white, yellow, and purple sweet potatoes across nine varieties. Results showed substantial differences in starch content, with white varieties having the highest was 61.5–67.5% and yellow the lowest was 45.8–53.1%. Starch granule sizes varied, with volume-weighted mean diameters ranging from 12.33 to 18.09 µm. All starches showed a CA-type crystalline structure with relative crystallinities between 22.8 and 25.6%. Swelling power and water solubility at 95 °C ranged from 25.2 to 31.1 g/gram and 11.7% to 16.6%, respectively, indicating that starch properties varied significantly among varieties and were influenced by genetic factors, not tuber color (Guo et al. 2019). Moreover, starch granules from the six cassava varieties exhibited a size range of 1.17–22.22 µm. Swelling power and solubility indices varied among the varieties, ranging from 2.22 to 15.63 g/gram and 1.62% to 71.15%, respectively. These properties were positively correlated with amylose content. Gelatinization temperatures showed onset, peak, and conclusion temperatures between 56.33–63.00 °C, 62.00–71.29 °C, and 69.10–77.12 °C, respectively, varying significantly among the varieties. Pasting temperatures ranged from 64.54 to 70.54 °C. The peak viscosity values ranged from 782.3 to 983.5 centipoise, with a noted negative correlation with amylose content. The freeze–thaw syneresis after five cycles varied significantly among the varieties, ranging from 0.00 to 42.40%. These properties were influenced by the starch's amylose, protein, lipid content, and granule size distribution (Shadrack Mubanga et al. 2019).
Moreover, the study on high-amylose wheat starch reveals distinct physicochemical and functional properties compared to wild-type wheat starch. High-amylose wheat starch exhibits about 1.5 times higher water absorption due to its less organized structure, broader gelatinization temperature ranges from 32 to 38 °C, while 13 °C for wild-type wheat starch, indicating a more heterogeneous molecular distribution, and significantly lower peak viscosity of 199 to 383 centipoise, while 1945 centipoise for wild-type wheat starch when analyzed using a high-temperature rapid visco analyzer. These properties, stemming from its higher amylose content and less branched amylopectin structure, make high-amylose wheat starch suitable for applications requiring lower viscosity and higher thermal stability (Li et al. 2020a). In addition, the physicochemical and structural properties of low-amylose starch from three Chinese yam (Dioscorea opposita) cultivars named Nuoshanyao, Tiegunshanyao, and Huaishanyao were studied, and the results showed that a broad range of gelatinization temperatures was 68.4–73.95 °C for onset temperature, 72.4–74.4 °C for peak temperature, and 76.8–78.2 °C for conclusion temperature, reflecting differences in crystalline structure due to varying amylose content of 17.0–34.5%. Peak viscosities varied significantly from 4794 to 8590 cP, higher in Nuoshanyao starch, indicating its potential for industrial use due to strong water absorption and retention capabilities. The crystallinity percentages ranged from 21.91 to 27.08%, correlating with the functional properties such as swelling power, which varied considerably across cultivars at different temperatures, and solubility, which showed less variation. These properties suggest distinct uses of each cultivar's starch in food and non-food industries, influenced by their structural characteristics at the molecular level (Shao et al. 2020).
Unripe plantain starch exhibits lenticular, elliptical, and semispherical morphologies. It includes both orthorhombic and hexagonal nanocrystalline structures, classifying it as C-type starch. X-ray diffraction confirmed these forms, and differential scanning calorimetry identified two endothermal events, indicating distinct solvation processes for each crystalline structure. The pasting properties, analyzed under a specific starch-to-water ratio (3:18), demonstrated a viscosity profile transitioning between a custard and a hydrogel. This complex behavior, particularly its dual crystalline nature and the ability to transition between physical states, suggests potential applications in food science, especially for products requiring unique viscosity and gelation characteristics (Vega-Rojas et al. 2021). Another study analyzed banana starches isolated from five Tanzanian varieties, revealing variations in physicochemical properties. Amylose content ranged from 29.92 to 39.50%, impacting properties like gelatinization, which showed onset temperatures from 57.33 to 62.51 °C and peak viscosities from 2248 to 2897 centipoise. These starches demonstrated significant resistant starch levels were 44.74% to 55.43%, beneficial for dietary applications. The granules, with particle sizes of 21.73 to 24.67 μm, exhibited B-type or C-type crystalline patterns, with crystallinity percentages from 36.69 to 41.83%. These properties suggest banana starch's potential to create stable viscosity products and indicate its adaptability in various food applications due to its unique structural and physicochemical characteristics (Yang et al. 2022a).
Furthermore, the physicochemical and functional properties of starch from four cassava and four yam cultivars were explored, and the results show significant differences influenced by their structural characteristics. Cassava starches displayed a lower amylose content of 9.43–22.22% compared to yam starches was 11.38–28.70%, which affected their processing properties. Yam starches required higher temperatures for gelatinization and exhibited higher viscosities and greater retrogradation potential, leading to firmer gel structures. In contrast, cassava starches had higher breakdown values during pasting, resulting in more fluid gels suitable for different culinary applications. These differences were attributed to variations in particle size, short-range ordered structure, protein content, and average radius of gyration. The study underscores the importance of considering these intrinsic properties when selecting starches for specific food and industrial applications (Zou et al. 2023). The study by Boahemaa et al. (2024) investigates the physicochemical and functional properties of taro starch extracted from two taro varieties, including KA/019 and BL/SM/16, focusing on their suitability for various applications. Starch yields were 16% for KA/019 and 11% for BL/SM/16, influenced by the mucilage content, which complicates extraction. Amylose content ranged from 20 to 25%, impacting functionality such as gelatinization and retrogradation. X-ray diffraction identified A-type crystallinity for both varieties, which is less common in root starches and indicates tighter molecular packing. The gelatinization temperatures were not specified, but higher amylose generally increases these temperatures, suggesting a more heat-stable starch. In vitro digestibility showed lower values for BL/SM/16, indicating its potential use in slow-digesting, low-glycemic-index foods. These findings highlight how inherent varietal differences in taro starch can dictate their application in food and possibly non-food industries, emphasizing the importance of selecting appropriate taro varieties based on desired starch characteristics (Boahemaa et al. 2024).
In conclusion, this section explores the diverse physicochemical and functional properties of starch derived from various plant sources, emphasizing how variations in structural attributes such as amylose content influence starch behaviors like gelatinization, solubility, and retrogradation. It details specific studies on starches such as barley, rice, and wheat, demonstrating the link between amylose levels and properties, including swelling power and paste viscosity. However, the presentation could benefit from a more cohesive analysis to enhance understanding of how these variations affect starch's practical applications in industries. While the examples are illustrative, integrating them with a clear discussion of their implications for industrial use would make the narrative more impactful and accessible, especially in elucidating the functional outcomes of these physicochemical properties.
Extraction
Starch extraction involves isolating starch granules from plant tissues, primarily from sources such as corn, potatoes, and wheat. The process starts with the pulverization of the plant material, followed by steeping in water to soften the tissues and release the starch granules. The mixture is then centrifuged or sieved to separate the starch from plant fibers and proteins. This slurry is further washed and dried to obtain pure starch (Fig. 4). Efficient extraction is crucial for maximizing yield and purity, directly impacting the quality and applicability of the starch in various industrial applications (Ghoshal and Kaur 2023; Liu et al. 2024b; Nie et al. 2023; Rashwan et al. 2023a).
A detailed flowchart for the production process of starch from plant-based sources. It starts with the raw materials of various plant-based starch sources such as corn, potatoes, and beans, which undergo a washing process to clean the raw material thoroughly. Following washing, the materials are crushed or subjected to wet milling, transforming them into a slurry. This slurry then moves through a sequence of processing steps: It is first filtered and separated, and then, it is passed through a desanding and desilting process to ensure purity. The clean starch solution or milk is further concentrated and refined, followed by dehydration and drying processes to produce both wet and dry starch. The final stages include sieving the starch to ensure a consistent powder form and packaging it for distribution, culminating in the starch powder or final product ready for various uses
The extraction method significantly impacts the quality of starch, affecting its purity, yield, molecular structure, and functional properties. For instance, wet milling typically results in higher-purity starch compared to dry milling by more effectively separating starch from proteins, lipids, and fibers (da Silva et al. 2020; Sorour et al. 2019). Methods including alkaline extraction can yield more starch due to the breakdown of structural components (Daiuto et al. 2005), whereas enzymatic extraction tends to preserve the native structure of starch, maintaining its thermal and pasting properties (Neeraj et al. 2021). The extraction process can also alter the amylose-to-amylopectin ratio by disrupting the granular structure, which in turn affects the gelatinization properties of starch. Additionally, the mechanical force used in some methods can shear the granules, affecting the size distribution and potentially damaging granule integrity. Moreover, the refinement of the extraction process influences the color and clarity of the starch, with more refined methods producing whiter and clearer starch solutions. Each extraction technique, whether mechanical, chemical, enzymatic, or physical, is chosen based on the raw material and desired characteristics of the final product, each presenting a trade-off between yield, purity, and functional properties (Kringel et al. 2020; Neeraj et al. 2021; Punia Bangar et al. 2022).
For example, using an oxalic acid/ammonium oxalate solution led to the most effective separation of starch from the residual mass due to reduced slurry viscosity, yielding 18 g of starch per 100 g of Dioscorea alata tuber, which is the highest among the tested methods. Other methods, such as water, sodium hydroxide, and pectinase, showed lower effectiveness, each with approximately 10% recovery. The size of starch granules also varied with the extraction method; the smallest starch granule diameter was 1.94 µm for using oxalic acid/ammonium oxalate and 13.5 µm for using water and pectinase, while the largest starch granule diameter was 41.0 µm for using sodium hydroxide solution and 67.7 µm for using oxalic acid/ammonium oxalate solution. This indicates that the choice of extraction method can significantly affect the yield, purity, and physical properties of the starch, which in turn can influence its suitability for various applications (Daiuto et al. 2005). Furthermore, the study evaluates the impact of various starch isolation methods from acorn kernels, specifically hot water soaking, alkaline washing, ultrasonic-assisted ethanol soaking, and ultrasonic-assisted hot water soaking. The study found that starch isolated using the ultrasonic-assisted ethanol soaking method exhibited superior properties, including the highest water solubility, swelling power, and the lowest tannin content, suggesting a highly efficient extraction process. Conversely, the alkaline washing method produced starch with the highest degrees of crystallinity and the whitest color, attributed to effective impurity removal. Additionally, starches derived from hot water soaking and alkaline washing methods demonstrated higher gelatinization temperatures, indicating a need for more energy to break down their crystalline structures, potentially offering better thermal stability (Zhang et al. 2020b).
Additionally, using a wet extraction process to extract the starch from three pigmented rice varieties, including white, red, and black varieties, preserved over 83% carbohydrates and phenolic compounds in the starches, enhancing their bioactive profiles, where wet extraction achieved yields of 44.0%, 47.0%, and 35.7%, respectively. After five freeze–thaw cycles, red rice starch gel exhibited the highest syneresis at 66.46%, followed by black rice starch gel at 51.39% and white rice starch gel at 31.18%. This indicates varying water retention capabilities among the starches, with red rice starch being the least stable under these conditions (da Silva et al. 2020). Four methods were assessed for starch isolation from sorghum: 24-h maceration with sodium sulfite and lactic acid, followed by grinding, sieving, and multiple washes; 3-h protease hydrolysis of ground grains; a combination of 12-h maceration and 3-h hydrolysis; and a combination of 24-h maceration and 3-h hydrolysis. Each method aimed to optimize starch purity and yield by removing proteins (Micaela and Drago 2020). Results showed starch recovery rates ranging from 43.5 to 75.5% and yields from 31.5 to 58%. The combined method of 24-h maceration followed by 3-h hydrolysis led to the highest starch recovery and quality, highlighting its effectiveness in releasing starch granules from the protein matrix. This method also resulted in starches with less residual protein and a higher whiteness index, indicating better purity and suitability for industrial uses (Micaela and Drago 2020).
Moreover, the effects of alkaline and enzymatic extraction methods on the morphology, color, and structural properties of starch from fruits of two acorns species, Quercus rotundifolia Lam. and Quercus suber Lam were examined. The results reveal that starches isolated using the enzymatic method exhibited higher lightness values, indicating a whiter color, while the alkaline method produced starches with a higher degree of crystallinity, up to 98.1%, suggesting less disruption to the starch's original structure. Starch granules were predominantly medium- to small-sized, with the majority being under 18 µm (Correia et al. 2021). Besides, the authors explored the effects of various extraction methods on the physicochemical properties of potato starch, comparing physical, chemical, and enzymatic techniques. They demonstrated that various methods distinctly impact starch yield and quality; for instance, using cellulase in enzymatic extraction increased the yield, whereas chemical extraction with sodium hydroxide enhanced water absorption and reduced ash content. More significantly, employing a combination of these methods substantially improved starch characteristics, boosting the yield to 12.4%, water absorption to 259%, swelling power to 40.3%, and whiteness to 95.2% while also decreasing phosphorus, protein, fat, ash, and crude fiber levels. Such enhancements in the starch's functional properties make it highly suitable for diverse industrial uses, highlighting the benefits of integrating multiple extraction methods to achieve superior starch quality (Neeraj et al. 2021).
The study examined starch extraction from Ramon seeds (Brosimum alicastrum) using two methods: distilled water and sodium hydroxide solution. The yields were 28.0% for distilled water and 31.9% for sodium hydroxide, with similar morphology, functional groups, and crystallinity for starches from both methods. The thermal properties were also comparable between the two methods, indicating their suitability for starch extraction from Ramon seeds. The results show that both extraction methods, distilled water and sodium hydroxide, effectively yield starch from Ramon seeds with minimal differences in physicochemical properties (Pech-Cohuo et al. 2021). The similar yields, crystallinity, and thermal behaviors suggest that both methods preserve the inherent properties of the starch granules, such as their spherical morphology and crystalline structure. The sodium hydroxide method slightly increased yield, possibly due to the more effective breakdown of plant cell walls, enhancing starch release. However, the comparable crystallinity and thermal properties between the two methods indicate that the chemical nature of the starch was largely unaffected by the choice of extraction solvent. This uniformity is crucial for applications where the functional characteristics of starch, such as gelatinization temperature and thermal stability, determine its suitability for industrial uses. The study supports the viability of both traditional including distilled water and chemical like sodium hydroxide extraction methods for obtaining starch from underutilized sources like Ramon seeds, which could be beneficial for developing sustainable biomaterials (Pech-Cohuo et al. 2021; Sorour et al. 2019).
Furthermore, Wang et al. (2021) evaluate ultrasonic-assisted enzymatic extraction of kiwi starch, achieving a 4.25% yield with a content of 873.23 mg per gram, featuring low gelatinization enthalpy 8.02 Joules per gram, high peak viscosity of 7933 centipoise, and significant antioxidant activity, along with high amylose of 30.74% and resistant starch of 60.18% contents. Compared to traditional methods, this approach is faster and more efficient, making it suitable for the industrial production of high-quality, functional starch. The low gelatinization enthalpy indicates that less energy is required for cooking, enhancing its convenience for food processing, while the high viscosity suggests its potential as a thickening agent. This innovative method not only optimizes starch extraction but also promotes sustainability in the kiwi industry by adding value to otherwise commercially non-viable kiwi fruits (Wang et al. 2021). In addition, the authors examined ultrasonic-assisted alkali extraction of pea starch, demonstrating an enhanced yield of 54.43% under optimal conditions, which is 13.72% higher than conventional alkali extraction. The extracted starch showed superior functional properties, including higher amylose content, water solubility, swelling power, and viscosity. Additionally, the resistant starch content was slightly increased. The ultrasonication did not alter the molecular or crystal structures significantly (Wang et al. 2022b). The enhanced yield and improved properties of the pea starch extracted using ultrasonic-assisted alkali methods can be attributed to the mechanical and cavitation effects of ultrasonication, which enhance the disruption and solubilization of starch components. The increase in amylose content and other functional properties suggests that ultrasonication modifies the starch structure in a way that potentially enhances its usability in various applications, such as food processing, where high viscosity and swelling power are beneficial. The slight increase in resistant starch content also suggests potential health benefits, as resistant starch can contribute to better digestive health (Wang et al. 2022b).
To summarize, the critical analysis of various starch extraction methods reveals significant differences in yield, purity, and functional properties depending on the technique employed. While traditional methods like wet milling provide high purity, innovative approaches like ultrasonic-assisted enzymatic extraction showcase higher efficiency and superior functional properties, such as increased amylose and resistant starch contents, which are beneficial for both nutritional and industrial applications. The study highlights the importance of selecting the appropriate extraction method based on the desired starch characteristics and the source material. Furthermore, the advancements in extraction technology not only optimize the yield and quality of starch but also contribute to the sustainability of the industry by enhancing the value of agricultural byproducts and reducing energy consumption. This emphasizes the need for ongoing research and development to refine these techniques and expand their application across different starch sources, potentially leading to more efficient, sustainable, and economically viable starch production processes.
Modification
Starches in their natural state have restricted functionalities that can limit their uses. Each type of starch has unique properties, including gelatinization temperature, water absorption rates at different temperatures, pasting capabilities, and gel strength, among other characteristics. Since the economically viable sources of starch are quite limited, producing modified starches has become a widely used alternative. This approach enhances the properties of starches to address one or more shortcomings of natural starches, thus expanding their industrial applications (Maniglia et al. 2021). Several properties of starch, including gelatinization, swelling, solubility, pasting, and retrogradation, can be altered through modification processes. These enhanced ingredients offer improved functionality in various applications compared to their unmodified forms, where modified starches are extensively utilized in the food industry for their thickening and gelling properties, serving as stabilizers, creating edible coatings, encapsulating food ingredients, delaying retrogradation, substituting fats, and increasing the content of resistant starch. To achieve these desirable properties, different modification methods are employed, including chemical, physical, enzymatic, and genetic techniques (Fig. 5) (Maniglia et al. 2021; Marta et al. 2022; Masina et al. 2017; Oktay et al. 2024; Punia Bangar et al. 2022; Wang et al. 2022a).
The modification methods of starch are organized into five primary categories: enzymatic, chemical, physical, genetic, and a combination of physical and chemical methods. Enzymatic modifications utilize specific enzymes to enhance starch solubility, digestibility, and functionality. Chemical modifications are subdivided into several processes such as hydrolysis, etherification, esterification, cationization, cross-linking, oxidation, graft copolymerization, and octenyl succinic anhydride modification, each altering the starch molecular structure to enhance various properties. Physical modifications are further organized into thermal treatments, such as simple heating, or more complex methods, like hydrothermal treatment, and nonthermal processes, including various forms of radiation, pressure, and ultrasonic treatments. Genetic modification involves altering the plant's DNA to optimize starch yield and quality, showing a direct intervention at the biological source
Among these, chemical modification is most used in the industry due to its cost-effectiveness and simplicity. This approach typically involves altering the hydroxyl groups at the C2, C3, and C6 positions of starch molecules through esterification, etherification, and oxidation, as well as depolymerizing the glycosidic bonds through chemical treatments (Masina et al. 2017). However, traditional chemical methods, such as the use of hypochlorite, acetates, phosphates, and acids, produce significant effluents that need to be managed due to their potential environmental harm. These effluents can introduce trace elements into the starch, restricting its use in sensitive applications like the pharmaceutical and food industries, which increasingly demand clean label ingredients (Oktay et al. 2024; Wang et al. 2023). Therefore, environmentally friendly methods can be used for the modification of starch properties without using harsh chemicals, making the starch more suitable for applications where chemical residues are undesirable, such as in food and pharmaceuticals. These methods include physical modification, enzymatic modification, and genetic modification. Each of these non-chemical modification methods offers unique advantages in terms of environmental impact, specificity, and suitability for different industrial applications, providing a wide range of possibilities for modifying starch to meet specific functional requirements (Maniglia et al. 2021; Oyeyinka et al. 2021; Punia Bangar et al. 2022; Wang et al. 2022a; Wang et al. 2023; Wang et al. 2020c). However, modified starches, achieved through physical and enzymatic processes, are seen as eco-friendly approaches to starch alteration. They fall under the category of "clean label ingredients" since they lack artificial or synthetic additives (Park and Kim 2021).
Physical modification
Physical modification methods involve physical processes such as heat–moisture treatment, dry heating treatment, ultrasonic treatment, microwave treatment, annealing, and high-pressure processing. Physical modification can change the crystallinity and gelatinization characteristics of starch. Techniques like heat–moisture treatment and pre-gelatinization are commonly used to enhance the solubility and digestibility of starch without altering its chemical structure (Wang et al. 2023). Ultrasonication involves using high-frequency sound waves to induce physical changes in the starch structure. This method can enhance the solubility and decrease the particle size of starch, making it more reactive and easier to use in food formulations (Hou et al. 2023). Besides, applying microwave energy to starch can induce changes like those achieved through conventional heating but in a more controlled and efficient manner. This can lead to alterations in the starch's crystalline structure and improved functional properties (Zhao et al. 2024).
For instance, pectin addition at 4 wt% concentration notably enhanced freeze–thaw stability and modified the retrogradation behavior of corn starch, as well as the heat–moisture treatment further improved these modifications. The combined pectin addition and heat–moisture treatment significantly reduced the retrogradation degree of corn starch to 39.7%, syneresis rate to 6.33%, double helices content to 26.5%, and leached amylose content to 22.7%. This is because heat–moisture treatment enhances the interaction between starch and other biopolymers, such as pectin. The heat–moisture treatment at controlled conditions includes a moisture level of 10–35% and temperature of 80–120 °C and does not damage the granular structure of starch but significantly modifies the morphology and functional properties of corn starch. This treatment leads to changes in the amorphous and crystalline regions within the starch granules, which affect its functional properties, such as gelatinization and retrogradation. The heat–moisture treatment was found to strengthen the hydrogen bonds between starch molecules (both amylose and amylopectin) and pectin, leading to a more stable and less retrograded starch structure. This stability is particularly evident in improved freeze–thaw stability, where the heat–moisture-treated starch shows reduced syneresis (water separation) rates, indicating less structural breakdown during freezing and thawing cycles (Zhang et al. 2021a).
Moreover, the effects of heat–moisture treatment on quinoa starch from Brazil were evaluated. The heat–moisture treatment was applied at 110 °C for durations of 1, 2, and 3 h, significantly influencing the thermal properties and gelatinization behavior. For instance, the onset temperature of gelatinization increased from 64.38 °C in native starch to 73.96 °C after 3 h of heat–moisture treatment. Similarly, peak temperatures rose from 73.13 to 81.53 °C. This shift can be attributed to the restructuring of hydrogen bonds within the starch granules and the partial crystallization that occurs during heat–moisture treatment, stabilizing the granule structure against thermal disruption. Structural analyses showed a decrease in relative crystallinity from 23.75% in native starch to 19.36% after 3 h of treatment. This effect is consistent with the observation that longer treatment times lead to a more amorphous starch structure, potentially improving its functionality in food applications by reducing retrogradation (the tendency of gelatinized starch to revert to a crystalline form upon cooling). Morphologically, scanning electron microscopy images revealed changes, including increased granule size and the appearance of surface cracks (Almeida et al. 2022).
The study evaluated the impact of repeated dry heating and continuous dry heating on wheat starch with varying amylose content, specifically normal and waxy wheat starches. The results found that repeated dry heating and continuous dry heating significantly modified the thermal, structural, and morphological properties of these starches. Repeated dry heating generally caused a greater decrease in crystallinity and thermal stability compared to continuous dry heating. Repeated dry heating also led to a more pronounced impairment of paste stability. After using repeated dry heating treatment, the gelatinization enthalpy decreased for waxy starch while gelatinization enthalpy increased for normal starch, suggesting a differentiated impact based on the amylose content (Zhang et al. 2021b). The differences observed between repeated dry heating, and continuous dry heating can be attributed to the cooling intervals inherent in repeated dry heating, which allow time for partial crystallization or reordering of the starch molecules. This intermittent cooling potentially results in a greater structural reorganization, influencing physical properties like crystallinity and thermal stability. For normal starch, the increased gelatinization enthalpy after repeated dry heating suggests a reassociation of starch molecules into a more ordered structure that requires more energy to melt. Conversely, the reduction in gelatinization enthalpy for waxy starch indicates a breakdown of structure, possibly due to the higher amylopectin content, which may be more susceptible to thermal disruption. Repeated dry heating appeared to influence the properties of starch more significantly than continuous dry heating, likely due to these intermittent structural reorganizations, which do not occur in the continuous exposure to heat in continuous dry heating (Zhang et al. 2021b).
Additionally, the effects of repeated dry heat treatment and continuous dry heat treatment on the physicochemical and structural properties of quinoa starch were studied. The results showed that the relative crystallinity increased from 38.60 in native starch to 44.83% for repeated dry heat-treated starch and increased to 42.96% for continuous dry heat-treated starch, water solubility increased from 3.9 to 10.0% and 10.9%, and pasting parameters, while decreasing swelling power of starch from 11.7 to 9.6% and 8.8% and water absorption index from 11.2 to 8.6% and 7.9%, respectively. Notably, repeated dry heat treatment led to a higher relative crystallinity and water absorption index compared to continuous dry heat treatment for the same duration. Moreover, repeated dry heat treatment samples showed lower water solubility, swelling power, paste viscosity, and thermal parameters than continuous dry heat treatment samples, indicating a differential impact based on the treatment method (Zhou et al. 2021).
Repeated dry heat treatment generally enhances the physicochemical and structural properties of quinoa starch more significantly than continuous dry heat treatment. This could be attributed to the cooling intervals in repeated dry heat treatment, which allow for partial crystallization and molecular reordering between the heating cycles. Such intervals are absent in continuous dry heat treatment, where the starch is subjected to continuous heat. This continuous exposure might limit the extent of molecular reordering compared to repeated dry heat treatment, resulting in lesser improvements in properties like crystallinity and water absorption. The enhanced relative crystallinity in repeated dry heat treatment samples suggests a more ordered structure, which could contribute to the observed reductions in paste viscosity and thermal parameters. The lower water solubility and swelling power in repeated dry heat treatment samples compared to continuous dry heat treatment samples can be linked to the more stable and ordered starch structure produced by repeated heating and cooling cycles. This structural stability likely reduces the starch's ability to absorb water and swell (Contreras-Jiménez et al. 2019; Oh et al. 2018; Zhou et al. 2021).
Ultrasonication significantly modifies the physicochemical properties of sweet potato starch by impacting its structural integrity and aggregation. After treating starch with ultrasonication for durations of 15, 20, 25, and 30 min, the crystallinity decreased from 31.6 to 26.1%, indicating a disruption in the organized crystal structures. Amylose content increases from 24.5 to 28.7%, suggesting that amylopectin is broken down into shorter amylose chains. Additionally, both swelling power and solubility are enhanced, reflecting greater water interaction due to the structural loosening. Pasting properties show a reduction in pasting temperature and viscosities, which points to altered gelatinization behavior, potentially making the starch more suitable for specific industrial applications where modified texture and viscosity are desired. These changes are driven by mechanical stress and cavitation from ultrasonication, which creates microfractures in starch granules, increases their porosity, and facilitates the breakdown of crystalline and amorphous regions (Wang et al. 2020a). Additionally, the effects of ultrasonic power and ultrasonic time on corn, potato, and pea starches were investigated, and the results demonstrated varied changes in starch structural, digestive, and rheological properties. Ultrasonication led to a decrease in apparent amylose content in corn and pea starches and an increase in potato starch, with apparent amylose content in corn starch dropping from 27.82 to 23.31% at 600-Watt ultrasonic power, suggesting that ultrasonic energy differentially affects starch types by disrupting or realigning amylose and amylopectin chains. Similarly, gelatinization enthalpy decreased across all starches, indicating a loss of thermal stability due to the breakdown of organized crystalline structures. The resistant starch content increased in corn starch while decreasing in potato and pea starches, reflecting altered digestibility due to changes in enzyme accessibility caused by structural disintegration. Rheological testing showed increased storage and loss moduli and decreased flow behavior index, suggesting that ultrasonication enhances the viscosity and elasticity of starch pastes by forming a denser network (Zhang et al. 2021c).
Furthermore, the study investigated the impact of ultrasonication on semigelatinized high-amylose maize starch, revealing significant changes in physicochemical properties and in vitro digestibility of treated maize starch. Ultrasonication did not increase gelatinization but led to structural modifications such as cracks and pores on the starch granules, and it increased the apparent amylose content. These structural changes enhance the formation of slowly digestible starch and resistant starch, particularly under high-temperature conditions. The mechanical and cavitation effects of ultrasonication are responsible for these outcomes, breaking down amylopectin chains and promoting the reformation of amylose into resistant structures, thus impacting starch digestibility. High-temperature ultrasonication effectively increased slowly digestible starch and resistant starch by enhancing amylose levels and promoting a tightly bound molecular structure that resists enzymatic breakdown, whereas low-temperature treatment reduced resistant starch content, likely due to less effective molecular rearrangements and retrogradation processes (Chan et al. 2021).
Besides, treating rice starch by vacuum combined ultrasound treatment resulted in significant shrinkage and damage to starch granules, reducing average particle size and altering the size distribution, making the starch more uniform. The lamellar architecture of the starch also changed, showing a reduced ordering degree, which indicates a disruption in the arrangement of starch molecules. Although the crystal type remained unchanged, there was a reduction in relative crystallinity, suggesting some degradation of crystalline regions. The thermal properties of the rice starch were modified, evidenced by decreased gelatinization enthalpy and temperature, pointing to altered thermal stability. The explanation for these results lies in the mechanisms of vacuum and ultrasound treatments, which include mechanical and cavitation effects. These forces disrupt the starch structure at a molecular level, affecting the organization and interaction of amylose and amylopectin within the starch granules. The vacuum helps in reducing air pockets within the starch, allowing for more effective ultrasound impact, which further contributes to starch breakdown and reorganization (Li et al. 2022b).
Moreover, Li et al. (2020b) demonstrated that microwave treatment of starch enhances its slowly digestible features, leading to increased slowly digestible starch content and a reduced rapid digestion rate compared to conventional heating. The results revealed through scanning electron microscopy and X-ray diffraction suggest that microwave treatment modifies the starch's physical and crystalline structures, making it more resistant to enzymatic digestion. Specifically, microwaves induce a transformation from A-type to B-type crystallinity and create a rougher and more fragmented granule surface, which hinders enzyme access and slows down the digestion process (Li et al. 2020b). Additionally, the effect of microwave treatment at 300 Watts for 1, 3, and 5 min on the physicochemical and structural properties of potato starch was analyzed by Kumar et al. (2020). Microwave treatment significantly increased water absorption capacity from 0.82 to 1.16 g/gram and decreased oil absorption capacity from 0.63 to 0.53 g/gram, highlighting changes in hydrophilic and hydrophobic properties, respectively. Pasting temperatures and viscosities correlated positively with treatment time, indicating alterations in starch gelatinization behavior. Dynamic and loss moduli, pasting temperatures, and final viscosities were positively correlated with treatment time. Scanning electron microscopy micrographs displayed smooth starch granules at 1 min of treatment, but fissures and indentations appeared at 3 and 5 min. X-ray diffraction patterns indicated a transformation from B-type crystallinity to an amorphous structure over time (Kumar et al. 2020).
Microwave treatment induced water evaporation and starch granule disruption, leading to changes in the absorption capacities and rheological properties. The increase in water absorption capacity suggests greater hydrophilic tendencies, likely due to the structural disruption enhancing water interaction. The decrease in oil absorption capacity might reflect a reduced number of hydrophobic sites or an altered interaction tendency of starch with oil. Morphological changes such as fissures and amorphization, evidenced by scanning electron microscopy and X-ray diffraction analyses, imply a restructuring that impacts starch's functional and digestive properties (Kumar et al. 2020; Li et al. 2020b). Besides, the surface roughness of sorghum starch granules increased while the pasting temperature and time increased, and the pasting viscosity and transition enthalpy decreased after using microwave treatment. Importantly, the in vitro digestibility of sorghum starch significantly reduced by 3.21–6.61%, rapidly digestible starch content decreased by 5.88–9.24%, slowly digestible starch and resistant starch contents increased by 4.63–6.65% and 1.03–2.41% respectively, and both the hydrolysis index and glycemic index decreased by 4.98–5.74% and 2.73–3.15% respectively. At the same time, microwave treatment causes structural disruptions in starch granules, leading to surface roughening and partial gelatinization. This affects the water absorption and swelling properties, which ultimately influence digestibility. Besides, the structural changes in starch, along with increased fiber content, decrease the starch's accessibility to digestive enzymes. This leads to lower digestibility and a lower glycemic index, which is beneficial for controlling blood sugar levels (Li et al. 2021).
In addition, the amylose content significantly increased from 25.5% in untreated starch to 27.4% in microwave-treated starch, where the increase in amylose content after microwave treatment suggests a partial debranching of amylopectin molecules, which leads to the release of linear amylose chains. This structural alteration contributes to the formation of more resistant starch, which is less readily digestible and thus beneficial for controlling blood glucose levels. The water-binding capacity of the sago starch rose from 1.1 to 1.6 g/gram, where the rise in water-binding capacity can be attributed to the morphological disruptions in starch granules that expose more hydrophilic sites, allowing for enhanced water absorption (Zailani et al. 2022). Besides, the solubility of the starch at 90 °C increased from 6% in the untreated sample to 26% in the treated sample, where the increased solubility is likely due to the breakdown of starch granules into smaller and less ordered fragments, which more readily dissolve in water. The peak viscosity of starch decreased from 850 Brabender units in the untreated to 650 Brabender units in the treated samples, indicating a reduction in the thickening power of the starch upon microwave treatment. The reduction in peak viscosity indicates that the gelatinization and swelling capacity of the starch are decreased due to microwave-induced damage to the granular structure. This change could affect the textural properties of foods where sago starch is used as a thickener. Scanning electron microscopy images also showed that microwave treatment caused surface disruption and the formation of fissures and cavities on the starch granules, which affect the water interaction and enzyme accessibility. The structural disruptions visualized through scanning electron microscopy contribute to the functional changes in starch behavior by increasing the surface area exposed to enzymatic attack, thereby reducing the digestibility of the starch (Zailani et al. 2022).
Dielectric barrier atmospheric cold plasma treatment was applied on Ariá (Goeppertia allouia) starch at various voltages, including 0, 7, 10, 14, and 20 kilovolts, and the results revealed significant modifications in the physicochemical properties of the starch. In which amylose Content decreased significantly from 0 kilovolts with increasing voltage, highlighting a significant depolymerization of starch molecules at 14 kilovolts but slightly higher amylose content at 20 kilovolts compared to 14 kilovolts. Here, the application of cold plasma led to structural changes within the starch, primarily through oxidative reactions facilitated by reactive species generated during plasma treatment (Carvalho et al. 2021). Besides, there was a notable reduction in pH with increasing plasma voltage, indicating acid formation likely due to increased oxidation, as well as carbonyl and carboxyl groups, which increased with higher voltages, reflecting more extensive oxidation and possibly the formation of new chemical bonds within the starch structure. Gel permeation chromatography analysis showed a decrease in molecular weight up to 14 kilovolts, indicating starch chain scission, but slightly increased molecular weights at 20 kilovolts, suggesting some reformation or cross-linking of starch molecules. These reactions include cross-linking (where starch molecules form new bonds, potentially increasing functionality) and depolymerization (breaking down of starch molecules, which affects viscosity and gelation properties). The overall increase in carbonyl and carboxyl groups indicates higher oxidation levels, which can influence the hydration properties and digestibility of the starch. In addition, the reduced pH and changes in molecular size distribution further corroborate the significant impact of plasma on starch's chemical structure, potentially enhancing its application in food industries where different textural properties are desired (Carvalho et al. 2021).
Scanning electron microscopy images revealed an elevation in surface roughness alongside the emergence of fissures and cracks on starch granules following cold plasma treatment, suggesting a significant alteration in their external morphology. This transformation potentially augments the granules' surface area and modifies their interactions within food matrices or industrial settings. Additionally, X-ray diffraction analysis displayed a reduction in the relative crystallinity index from 29.5% in untreated starch to 25.8% post-treatment, indicating a disruption in the ordered crystalline structure and a shift toward a more amorphous state. Such structural modifications can influence various functional properties of starch, including gelatinization behavior and stability during processing (Sun et al. 2022). Differential scanning calorimetry measurements also showed a decrease in gelatinization enthalpy from 13.8 Joules per gram in untreated starch to 10.2 Joules per gram after treatment, indicating a lowered energy requirement for starch granule disruption and gelatinization initiation. Moreover, cold plasma treatment led to diminished peak viscosity from 1950 centipoise in untreated starch to 1600 centipoise post-treatment, along with a reduction in breakdown viscosity from 760 to 610 centipoise, signifying altered pasting properties affecting the stability of starch paste formation during thermal cycles. Conspicuously, in vitro enzymatic digestion assays indicated a decline in rapidly digestible starch content from 32.1 to 25.6% following treatment, coupled with an increase in resistant starch content from 11.5 to 17.8%, suggesting an enhancement in the resistance of rice starch to enzymatic hydrolysis and a slower release of glucose during digestion (Sun et al. 2022).
Furthermore, Zhang et al. (2021c) investigated the effects of ultra-high pressure on lily starch and revealed significant modifications in starch morphological and physicochemical properties, with the detailed observation that ultra-high-pressure treatment led to the expansion and aggregation of starch granules, particularly at 600 megapascals, where almost complete gelatinization occurred. This was further substantiated by scanning electron microscopy images that displayed disrupted morphology and an increase in particle sizes at elevated pressures. Ultra-high-pressure treatments considerably influenced the particle size distribution, evidenced by a notable shift to larger particle sizes at 600 megapascals, signaling extensive starch aggregation. The relative crystallinity of the starch showed a decline as pressure increased, with a sharp decrease at 600 megapascals, suggesting a substantial disruption in its crystalline structure and a transformation toward a more amorphous state. Moreover, gelatinization temperatures decreased under higher pressures, indicating that lower energy is needed to disrupt the granular structure due to the changes induced by ultra-high pressure. At 600 megapascals, ultra-high-pressure treatment significantly reduced the peak viscosity, trough viscosity, breakdown, final viscosity, and setback of the starch, reflecting deep modifications in how the starch interacts with water and undergoes gelatinization (Zhang et al. 2021c).
These modifications are primarily due to the intense pressure disrupting intermolecular bonds within the starch granules, thereby enhancing water penetration and facilitating gelatinization. The notable decrease in crystallinity coupled with changes in thermal and pasting properties suggests that the starch structure becomes less organized, making it more receptive to water interaction and heat (Colussi et al. 2020; Zhang et al. 2021c). Moreover, the average particle size of oat starch dramatically increased from 10.35 µm in untreated samples to 20.83 µm after 30 min of high-hydrostatic-pressure treatment at 500 megapascals, indicating significant swelling and aggregation of the starch granules under pressure. Consequently, the relative crystallinity of oat starch showed a substantial decrease from 36.86% in the control to 13.79% after 30 min of treatment, suggesting extensive disruption of the starch's ordered crystalline structure due to high hydrostatic pressure. Furthermore, the onset temperature for gelatinization of untreated oat starch was 160.76 °C, which decreased to 116.68 °C after 30 min of high-hydrostatic-pressure treatment, implying that less energy was required to initiate gelatinization due to the structural changes induced by high hydrostatic pressure. Additionally, the peak viscosity of oat starch decreased from 495.10 millipascal seconds in the control to 433.20 millipascal seconds after 30 min of high-hydrostatic-pressure treatment, reflecting a diminished ability of the starch to thicken or stabilize mixtures due to the treatment (Zhang et al. 2022a).
Moreover, the content of rapidly digestible starch initially decreased after 5 min of high-hydrostatic-pressure treatment compared to the control but subsequently increased with longer treatment durations, peaking after 30 min, indicating changes in digestibility profiles that suggest initial resistance to enzymatic breakdown, which diminishes with prolonged exposure (Zhang et al. 2022a). This increase in particle size and the decrease in crystallinity can be attributed to the pressure disrupting the internal structure of the starch granules, making them more amorphous and prone to swelling, leading to larger aggregates as the granules absorb more water and merge. Finally, the decrease in the onset temperature for gelatinization and reduction in peak viscosity reflects a loss in molecular order and a decrease in the entanglement of starch molecules, which typically contribute to the viscosity of starch pastes and require higher thermal energy to overcome the structural resistance of the starch matrix (Colussi et al. 2020; Zhang et al. 2021c; Zhang et al. 2022a).
High-pressure treatment significantly impacted the structure and functionalities of potato starch, particularly when combined with heat–moisture treatment. While high hydrostatic pressure alone did not significantly modify most pasting properties, high hydrostatic pressure in combination with heat–moisture treatment notably increased peak viscosity from 1743 centipoise in control to 1972 centipoise in high hydrostatic pressure in combination with heat–moisture treatment sample, setback viscosity from 544 cP to 685 centipoise, and final viscosity from 1277 to 1562 centipoise. This indicates improved starch gelatinization and pasting properties, likely due to high hydrostatic pressure breaking down starch granules and enabling better water binding and swelling during subsequent heat–moisture treatment (Colussi et al. 2020). Additionally, high-hydrostatic-pressure treatment decreased swelling power from 11.2 g per gram in the control sample to 10.3 g per gram and solubility from 5.4% to 4.8%, indicating reduced water absorption capacity and solubility of starch granules post-treatment, possibly due to structural changes induced by high hydrostatic pressure compacting the granules. Gelatinization temperatures increased after high-hydrostatic-pressure treatment, with onset temperature rising from 62.5 °C in the control sample to 64.3 °C and peak temperature from 71.2 to 72.8 °C, suggesting increased thermal stability attributed to strengthened intermolecular bonds within the starch matrix. Scanning electron microscopy revealed smoother surfaces post-treatment, while X-ray diffraction analysis showed a decrease in relative crystallinity, indicating a disruption in the ordered crystalline structure of starch granules (Colussi et al. 2020).
Additionally, the modification of early indica rice starch through annealing treatments with microwave pre-treatment at 540 watts for 0, 10, 20, and 30 min yielded significant changes in starch structural and physicochemical properties. The relative crystallinity of rice starch treated with annealing and microwaving for 20 min showed a substantial increase, recording 25.38%, while annealing and microwaving for 30 -minutes recorded 24.34%, compared to the native starch at 22.18% (Zhong et al. 2020). This enhancement suggests that microwave pre-treatment facilitates the reorganization of starch molecules, which enhances the effectiveness of subsequent annealing, leading to a more perfect long-range crystalline structure. Besides, the scanning electron microscope analysis revealed that the granular morphology of the starch was noticeably altered by the treatments. Pasting properties were also significantly influenced; although specific values were not detailed, it is indicated that the treatments modify the starch's interaction with water and its gelatinization behavior, which could be crucial for applications requiring specific viscosity characteristics. In essence, the combined microwave and annealing treatment effectively alters the structural integrity and functional properties of early indica rice starch, which could lead to expanded applications in food products by improving properties like thickening and stabilization (Zhong et al. 2020).
Furthermore, various combinations of microwave and ultrasound treatments were applied to corn starch. For the ultrasound–microwave treatments, the ultrasound was conducted at a constant temperature of 35 °C for 20, 30, or 40 min, followed by microwave treatments at power settings of 90, 180, 360, and 600 Watts for 1, 2, or 3 min. Similarly, for the microwave–ultrasound treatments, the sequence was reversed, starting with the same microwave settings followed by ultrasound under the same conditions. A noticeable decrease in the broadband intensity at around 3400–3600 cm−1 was observed, which corresponds to the hydroxyl groups of amylose and amylopectin (Yılmaz and Tugrul 2023). This reduction suggests a loss of starch's capacity to bind water after treatments. Changes in the absorption bands at 1150 and 1040 cm per inverse were noted, indicating alterations in the crystalline structure of the starch toward a more amorphous state. Native corn starch typically presents a smooth, rounded morphology. After treatment, significant morphological changes such as surface roughness and the emergence of an irregular and amorphous granular structure were evident. The extent of granular disruption increased with higher microwave power and longer ultrasound duration. At 360 Watts and 30–40 min of ultrasound, the starch granules exhibited the most substantial deformation, indicating an optimal condition for maximum modification efficiency (Yılmaz and Tugrul 2023).
The combination of ultrasound and microwave treatments modifies the corn starch by primarily disrupting its crystalline structure and promoting amorphous characteristics. These changes can be attributed to several mechanisms. Ultrasound generates cavitation, such as microbubbles that form and collapse violently, producing high shear forces that physically disrupt the starch granules. This disruption facilitates the penetration of water, altering the hydration properties of the starch. Microwave treatment induces dielectric heating, which unevenly heats parts of the starch granules, creating localized stress points that lead to a structural breakdown. This uneven heating is more pronounced at higher wattages, leading to more significant disruption. The sequential application of ultrasound and microwave treatments combines mechanical and thermal stresses, enhancing the overall disruption and modification of the starch structure. This synergism is evident from the significant changes in morphological and chemical properties observed under combined treatment conditions (Yılmaz and Tugrul 2023).
To summarize, physical modification methods, such as heat–moisture treatment and ultrasonication, highlight their effectiveness in enhancing starch functionality without chemical alteration. Techniques such as adding pectin and controlling heat–moisture conditions significantly improve properties like freeze–thaw stability and retrogradation behavior of corn starch. These methods enhance the interaction between starch and biopolymers, strengthening hydrogen bonds and modifying structural regions, which improve the starch's functional properties for industrial applications. Additionally, the combination of various physical modification methods, such as microwave and ultrasound treatments, effectively disrupts the crystalline structure, making the starch more amorphous and reactive for diverse formulations. This illustrates significant advancements in starch modification through controlled physical processes.
Enzymatic modification
Enzymatic modification methods, where enzymes can be used to modify the structure of starch molecules selectively. This process involves hydrolyzing the starch using specific enzymes, including amylase, glucanase, or pullulanase (Fig. 6), which can cleave the bonds within the starch molecules, resulting in modified gelatinization and retrogradation properties (Kennedy et al. 1988; Punia Bangar et al. 2022). Besides, enzymes exhibit remarkable specificity, minimizing the formation of undesirable byproducts, unlike the random glycosidic linkage attacks in acid-thinning or chemical modification. Retrieval of enzymes is easier compared to acids, while the mild enzymatic reaction lowers activation energy, facilitating substrate conversion and enzyme reuse. Enzymatic methods, especially sub-gelatinization, are replacing chemical and physical approaches, offering safer and healthier outcomes for both the environment and consumers. Additionally, enzymatic processes reduce energy costs and ensure higher yields, thanks to their specificity for starch substrates within complex food matrices (Al-Maqtari et al. 2024; Punia Bangar et al. 2022).
Enzymatic hydrolysis of starch involves the breakdown of starch molecules into smaller carbohydrate units through the action of specific enzymes. A non-reducing D-glucosyl residue refers to a glucose molecule that is part of a larger carbohydrate structure but does not have a free-reducing end. In other words, non-reducing D-glucosyl residue is not capable of reducing other compounds because its anomeric carbon is involved in a glycosidic bond, preventing it from forming a hemiacetal or hemiketal group. These residues are often found in polysaccharides like starch and cellulose, where glucose units are linked together through glycosidic bonds. A reducing D-glucosyl residue, also known as D-glucose, is a molecule of glucose that has the potential to reduce other substances due to the presence of a free aldehyde group at the anomeric carbon. This aldehyde group can undergo oxidation reactions, allowing the glucose molecule to act as a reducing agent
Starch-modifying enzymes can be categorized into two main groups including glycosyl hydrolases and transglycosylases. These enzymes, crucial for modifying starch, include α-amylase as maltogenic amylase, β-amylase, amylosucrase, cyclodextrin glycosyltransferase, 4-α-glucanotransferase amylomaltase, and glucan transferase as branching enzyme, as well as pullulanase and isoamylase as debranching enzymes. Glycosyl hydrolases break down glycosides' glycosidic bonds, producing a sugar hemiacetal and a free aglycon, as well as transglycosylases convert one glycoside into another. These enzymes are sourced from microorganisms such as Thermus sp., Bacillus stearothermophils, Bacillus acidopullulyticus, Aspergillus niger, Bacillus subtilis, Bacillus magaterium, Neisseria polysaccharea, Deinococcus geothermalis, Rhodothermus obamensis, Aquifex aeolicus, and Deinococcus radiodurans. Some enzymes are also derived from plants such as ramie leaf and barley, including amylases (Al-Maqtari et al. 2024; Christensen et al. 2023; Punia Bangar et al. 2022; Zhong et al. 2021a).
The enzymatic treatment of high amylose rice starch using amyloglucosidase and maltogenic α-amylase significantly altered its structural and functional characteristics, as evidenced by the development of distinctly different pore sizes and patterns on the starch granules. Specifically, amyloglucosidase treatment produced larger, more superficial pores, and after 24 h of treatment, the relative crystallinity of the starch increased to 29.02%, indicating a progressive enhancement in structural order due to prolonged enzyme exposure. In contrast, maltogenic α-amylase treatment resulted in the formation of smaller, deeper pores, achieving a peak crystallinity of 33.29% after just 12 h; however, this crystallinity decreased to 27.82% at 24 h, reflecting the extensive enzymatic activity that continues over time (Keeratiburana et al. 2020). The molecular weight of the starch was dramatically reduced by maltogenic α-amylase, from an initial 5.75 × 107 to 0.98 × 107 Daltons at 24 h, highlighting the enzyme’s intense starch chain breakdown capabilities compared to amyloglucosidase. While both enzymes diminished the swelling capacity of the starch, their impact on solubility differed; amyloglucosidase decreased the solubility to 0.10% at 24 h, suggesting a reorganization into a less soluble structure, whereas maltogenic α-amylase increased the solubility to 2.56%, likely due to the production of smaller, more soluble amylopectin chains. Moreover, the pasting properties of the starch were also significantly modified by both enzymes, evidenced by reductions in peak viscosity and breakdown; amyloglucosidase treatment led to a 15% reduction at 24 h, while maltogenic α-amylase treatment saw a more pronounced reduction of up to 31%. These changes indicate that the enzymatically modified starches are less capable of reassociating to form a viscous gel, highlighting the distinct effects of amyloglucosidase and maltogenic α-amylase on the functional properties of high amylose rice starch (Keeratiburana et al. 2020).
Furthermore, the treatment of corn starch with maltogenic α-amylase followed by transglucosidase resulted in a significant reduction in the molecular size of amylopectin, with a notable increase in the proportion of short amylopectin chains having a degree of polymerization less than 10. Specifically, there was a more than 20% relative increase in chains with a degree of polymerization less than 10, alongside a decrease in chains with a degree of polymerization ranging from 10 to 28. Wide-angle X-ray scattering revealed an initial decrease in crystallinity following the enzymatic treatments, which highlights the disruption of the starch's ordered structure (Zhong et al. 2021b). Interestingly, after an extended 20-h treatment with transglucosidase, the crystallinity measurements rebounded to baseline levels, indicating a possible structural reordering or recrystallization within the starch. Quantitatively, the study also measured how these enzymatic treatments retarded starch retrogradation, observing that both the storage modulus (elastic response) and loss modulus (viscous response) of the starch gel were significantly reduced, suggesting a slower retrogradation process compared to untreated starch. Maltogenic α-amylase primarily functions by breaking down amylopectin chains to increase the number of chain ends, which transglucosidase then further modifies through its glycosidic bond-breaking and transglycosylation activities, resulting in an increased number of shorter, more branched amylopectin chains. This sequential enzymatic modification not only alters the pasting properties of starch, making it more suitable for various industrial applications, but also improves product shelf life and textural stability, which is advantageous in sectors like food processing and pharmaceuticals (Zhong et al. 2021b).
Moreover, the modification of granular waxy, normal, and high-amylose maize starches by maltogenic α-amylase revealed significant alterations in their structural and functional characteristics, demonstrating varying degrees of susceptibility and reaction across different starch types. Waxy maize starch was highly susceptible to enzymatic hydrolysis, with the rate increasing from 22.5% at 4 h to 39.7% at 24 h, while normal maize starch also showed substantial hydrolysis, escalating from 19.8% at 4 h to 35.9% at 24 h. In contrast, high-amylose maize starch exhibited a lesser effect, with hydrolysis rates only reaching 11.2% at 24 h. The pasting viscosities of both waxy and normal maize starches were significantly reduced; for instance, waxy maize starch's peak viscosity decreased from 2295 to 1021 cP after 4 h and continued to drop with prolonged treatment (Li et al. 2022a). Interestingly, the resistant starch content in cooked normal maize starch increased significantly from 2.6% in the untreated sample to 7.3% in the maltogenic α-amylase-treated sample, suggesting a formation of retrograded amylose, which is beneficial for increasing the dietary fiber content of foods. Maltogenic α-amylase preferentially shortened the amylopectin branches in these starches, reducing their ability to reassociate into ordered structures during cooling, thereby diminishing retrogradation; this property is especially beneficial for applications where texture and stability over time are crucial, such as in baked goods and refrigerated or frozen foods. These enzymatic modifications tailored to different maize starch types highlight the potential to enhance or modify starch functionalities for specific food applications, offering improved shelf life and texture for processed foods while demonstrating the limitations in high-amylose starch due to its resistance to enzymatic action (Li et al. 2022a).
Additionally, the study explored the modification of potato starch using six distinct GH77 4-alpha-glucanotransferases from various microbial sources including Thermus thermophilus (Tt4αGT), Akkermansia glycaniphila (Ag4αGT), Bifidobacterium longum (Bl4αGT), Corynebacterium glutamicum (Cg4αGT), Bacteroides thetaiotaomicron (Bt4αGT), and Lactococcus lactis (Ll4αGT), which revealed significant differences in their starch modification capabilities. Among these, Tt4αGT from Thermus thermophilus exhibited the highest efficiency, substantially reducing amylose content and promoting extensive amylopectin chain elongation, thus enhancing the starch’s ability to form stable gels. The degree of amylose depletion was most pronounced with Tt4αGT, which was crucial to producing robust gels (Christensen et al. 2023). This enzyme, along with Ag4αGT and Cg4αGT, was particularly effective in elongating amylopectin chains, with Tt4αGT significantly increasing the concentration of longer chains (DP25-55), a factor that correlates with improved gelling properties. The ability to form firm and stable gels varied among the enzymes, with Tt4αGT, Ag4αGT, and Cg4αGT producing gels that withstood inversion tests, indicating their potential utility in food applications that require strong textural characteristics. The superior performance of Tt4αGT can also be attributed to Tt4αGT optimal activity at higher temperatures like 73 °C, making Tt4αGT suitable for processes demanding thermal stability. The differences in starch modification abilities among these enzymes likely stem from variations in their molecular structures, such as the presence of additional carbohydrate-binding modules or domains of unknown function, which influence their interactions with starch molecules and ultimately affect their efficiency in altering starch properties (Christensen et al. 2023).
After treatment of sorghum starch with pullulanase hydrolysis combined with infrared, the hydrolysis rate constant was significantly reduced to 0.022. Additionally, the hydrolysis index, which measures the relative speed of digestion compared to a standard, decreased to 42.58, showing a marked reduction in the rate at which the starch is broken down by digestive enzymes. The potential digestibility of the starch was lowered to 0.468, indicating the maximum proportion of starch that could be digested under prolonged enzymatic action, highlighting a substantial decrease in digestibility due to the treatments. The amylose content in the starch increased up to 31.31%, and crystallinity increased to 62.66%, indicating significant structural modification, making the starch more resistant to enzymatic breakdown (Semwal and Meera 2023). Besides, the pullulanase enzyme specifically targets the amylopectin fraction of starch, cleaving its branches and increasing the relative amount of linear amylose. This increase in amylose content is crucial for decreasing digestibility as amylose is less readily broken down by enzymes than amylopectin due to its helical structure, which is tightly packed and less accessible to enzymes. The increase in crystallinity from 62.66% suggests more ordered and tightly packed molecular structures within the starch granules, forming a physical barrier that slows down enzymatic attack, further reducing starch digestibility. The modified starch exhibited decreased pasting properties, indicating a significant reduction in viscosity during heating, particularly peak viscosity, and breakdown viscosity, suggesting less tendency to swell and break down under heat, beneficial for stable, low-thickness pastes over prolonged heating periods. These changes point toward the utility of this modified starch in foods designed for slow glucose release, such as in diabetic diets or in applications where controlled release of nutrients is desired, targeting health conscious consumers managing blood glucose levels (Semwal and Meera 2023).
Further, the study focused on the two-step enzymatic modification of rice starch with pullulanase and transglucosidase, aiming to enhance gel strength and reduce starch digestibility. Gel strength, measured by hardness, notably improved, particularly after 18 h of transglucosidase treatment, significantly increasing compared to both native and initially pullulanase-treated starches, attributed to longer and more branched starch molecules forming a cohesive gel structure. Starch digestibility substantially decreased, indicated by lower hydrolysis rates, notably after 18 h of transglucosidase treatment, suggesting a structure less prone to enzymatic breakdown, reflected in the digestion rate constant, markedly lower in transglucosidase-treated samples than native starch. The hydrolysis index in transglucosidase-treated starches showed up to a 20% decrease compared to native starches, confirming reduced digestibility (Geng et al. 2024). Besides, gel hardness increased by 30–40% after 18 h of transglucosidase treatment compared to pullulanase-only-treated starch. Initial pullulanase treatment debranches amylopectin, forming longer linear chains initially less organized, decreasing gel strength, but subsequent transglucosidase treatment increases branching within these chains, enhancing gel strength. Transglucosidase-modified starch, with increased branching and complex molecular architectures, is less accessible to digestive enzymes, resulting in slower digestion, which is beneficial for reducing starch-based foods' glycemic index. Modified starch, with increased gel strength and reduced digestibility, suits products needing low glycemic index and robust texture, like pastries, noodles, and extended shelf-life prepared foods. The modification process, showing scalability potential, suggests its adoption in industrial settings to produce starches tailored for specific functional requirements in food processing (Geng et al. 2024).
To summarize, enzymatic modification methods offer targeted alteration of starch molecules, enhancing their structural and functional properties with minimal formation of undesirable byproducts compared to chemical approaches. The use of specific enzymes like pullulanase and transglucosidase results in significant reductions in starch digestibility, accompanied by increases in amylose content and crystallinity, rendering the starch more resistant to enzymatic breakdown. These modifications improve the pasting properties and stability of the starch, making it suitable for applications requiring controlled glucose release, thus catering to the needs of health conscious consumers while offering potential for scalable industrial production.
Genetic modification
Genetic modification of starch advances in biotechnology enables the alteration of starch-producing crops at the genetic level to produce starches with desired properties directly from the plant. By modifying the genes responsible for starch biosynthesis in crops such as corn, potatoes, and rice, genetic modification is possible to enhance specific traits such as amylose content, branch chain length, and resistance to retrogradation (Amaraweera et al. 2021; Andersson et al. 2006; Schwall et al. 2000).
For example, the study by Schwall et al. (2000) successfully produced very-high-amylose potato starch by simultaneously inhibiting starch branching enzymes 1 and 2, resulting in significant modifications to starch composition and properties. Transgenic lines exhibited amylose contents ranging from 60 to 89%, with the highest lines displaying up to 75% amylose by colorimetric methods and up to 89% by potentiometric methods. These high-amylose starches showed a dramatic increase in phosphorus content, up to 3000 µg/g, approximately six times higher than wild-type starch, accompanied by altered granule morphology with reduced birefringence and irregular surfaces. The simultaneous inhibition of starch branching enzymes 1 and 2 led to a drastic reduction in branched amylopectin synthesis, resulting in starch predominantly consisting of linear amylose chains (Schwall et al. 2000). This alteration not only elevated amylose content but also significantly changed starch properties, including increased phosphorus content, and altered pasting behavior. The absence of high molecular weight amylopectin and increased phosphorus content suggest a structural shift in starch granules toward enhanced phosphate binding, possibly due to altered glucose molecule arrangement in highly linear amylose chains, which could expose more phosphate attachment sites. These modifications render the starch suitable for novel applications in food and industrial processes where high-amylose starches are valued for their distinct textural and digestibility characteristics (Schwall et al. 2000).
Besides, the targeted gene suppression by ribonucleic acid interference in high-amylose potato lines demonstrated substantial increases in amylose content due to the inhibition of the starch branching enzymes 1 and 2. The genetically modified high-amylose potato lines achieved an amylose content increase from the typical 20–30% found in normal potatoes to about 70–80% of total starch content. The modification led to significant changes in the starch granule morphology, impacting the digestibility and functionality of the starch. The effective suppression of starch branching enzymes 1 and 2 through ribonucleic acid interference was instrumental in increasing the proportion of amylose in the starch composition. Starch branching enzymes are typically responsible for the branching in amylopectin; thus, inhibiting these enzymes leads to a higher ratio of linear molecules (amylose) to branched molecules (amylopectin). The increase in amylose content significantly altered the physical properties of the starch. High-amylose starches are known for their reduced digestibility and increased resistance to enzymatic breakdown, which can enhance the formation of resistant starch. This form of starch contributes positively to dietary fiber intake and has associated health benefits, such as improved glycemic control and increased satiety (Andersson et al. 2006).
Additionally, the research demonstrated the use of CRISPR-Cas9 for targeted modifications in cassava, specifically targeting the granule-bound starch synthase and protein targeting to starch 1 gene, leading to significant changes in starch composition and accelerated breeding processes. The editing of granule-bound starch synthase resulted in the production of starch with virtually no detectable amylose. Quantitative measurements indicated that typical cassava starch has about 20% amylose, whereas the gbss-TAH edited lines showed amylose content effectively reduced to 0%. In comparison, modifications involving protein targeting to starch 1 also decreased amylose content but not as drastically, indicating a more auxiliary role of protein targeting to starch 1 in amylose biosynthesis. Integration of the Arabidopsis FLOWERING LOCUS T gene into cassava achieved flowering initiation within just 12 weeks under controlled glasshouse conditions. This is a remarkable advancement, considering that cassava usually takes a year or more to reach reproductive maturity under natural conditions. The CRISPR-Cas9 system was employed to create knockout mutations in the granule-bound starch synthase gene, directly disrupting the enzymatic pathway responsible for amylose synthesis (Bull et al. 2018).
This precise genetic intervention effectively eliminates the production of amylose, which is crucial for applications requiring high-amylopectin starches, such as in the textile and food industries where clear gels and pastes are preferred. Protein targeting to starch 1 edit, while also reducing amylose content, primarily affected the enzyme's localization rather than its synthesis. This suggests that protein targeting to starch 1 role involves the transport or positioning of granule-bound starch synthase within the starch granules, a critical factor for optimal enzyme function in amylose production. The introduction of the Arabidopsis FLOWERING LOCUS T gene represents a significant innovation in cassava breeding (Bull et al. 2018). By accelerating the flowering process, this genetic addition cuts down the breeding cycle drastically, facilitating quicker studies and faster propagation of modified traits. This is particularly useful for breeding programs in non-tropical environments where cassava’s growth cycle is naturally prolonged. The ability to produce amylose-free cassava starch in a shortened timeframe has profound implications for both agriculture and industry. It allows for the rapid development of cassava varieties tailored for specific industrial applications while also enhancing the crop's adaptability to different climatic conditions, potentially expanding its cultivation outside traditional tropical environments (Bull et al. 2018).
The high-amylose potato line T-2012, derived from the parental cultivar Dinamo, was created via genetic modification involving the downregulation of two starch-branching enzyme genes, including SBEI and SBEII, and evaluated for the content of resistant starch and dietary fiber. The findings revealed that uncooked high-amylose tubers contained 30% resistant starch of dry matter, a significant decrease compared to the parent cultivar, 56% of dry matter. Upon cooking, resistant starch content in high-amylose tubers rose to 13% of dry matter, increasing further to approximately 20% after one day of cold storage tubers (Zhao et al. 2018). Additionally, high-amylose tubers exhibited heightened dietary fiber content of 10–14% of dry matter compared to the parent 5–7% of dry matter, including elevated levels of cellulose and reduced pectin. The genetic modifications implemented in the high-amylose potatoes, which targeted starch synthesis pathways, resulted in modified starch granule structure and amylopectin architecture, likely contributing to the observed variations in resistant starch and dietary fiber content. Cooking altered the starch properties, promoting RS formation, while the increase in RS after cold storage (retrogradation) indicated a realignment of amylose and possibly altered amylopectin, forming structures resistant to digestive enzymes. Moreover, the genetic modifications influenced cell wall components, leading to an increase in cellulose and a decrease in pectin, which could affect the overall dietary fiber content and nutritional properties of the tubers (Zhao et al. 2018).
In conclusion, the advancements in biotechnology allow for targeted modifications in starch-producing crops like corn, potatoes, and rice, enabling the enhancement of specific traits such as amylose content and resistance to retrogradation. For instance, the creation of very-high-amylose potato starch through genetic modification resulted in significant changes in starch composition and properties, including increased amylose content and altered granule morphology. Similarly, the use of CRISPR-Cas9 in cassava led to the production of amylose-free starch, demonstrating the potential to accelerate breeding processes and tailor crops for specific industrial applications. These developments offer promising avenues for improving food and industrial processes, emphasizing the crucial role of genetic modification in enhancing starch functionalities and nutritional value.
Green applications
Starch stands out as one of the most economical materials with considerable potential in the production of solid plastics and other functional polymers. Predominantly synthesized by plants, starch is found in varying concentrations was 25–90% in cereals, root tubers, fruits, and legumes. Starch can be used in several applications, such as a food stabilizer, meat replacer, and resistant starch serving as a prebiotic. Additionally, starch can be used to prepare encapsulation systems, as a component in three-dimensional food printing, wood adhesives, the textile industry, and the production of bioplastic and edible films (Fig. 7). Starch’s appeal for advanced materials applications derives from its broad geographic availability across various plant sources, coupled with its low cost and abundance (Amaraweera et al. 2021; Bühler et al. 2022; Chen et al. 2024; Hasanin 2021; Liu et al. 2017; Park and Kim 2021; Rong et al. 2023; Singla et al. 2020; Sohouli et al. 2022; Tiozon et al. 2021).
Applications of starch in various industries. Starch can be used in several applications, such as a food stabilizer, meat replacer, and resistant starch serving as a prebiotic. Additionally, starch can be used to prepare encapsulation systems as a component in three-dimensional food printing, wood adhesives, the textile industry, and the production of bioplastic and edible films
Food stabilization
Starch’s remarkable ability to modify viscosity, enhance texture, and prolong shelf life makes it invaluable in food formulation. As a stabilizer, starch interacts with water molecules, forming a gel-like structure that thickens and stabilizes food products. This stabilizing effect is particularly crucial in preventing ingredient separation, maintaining consistency, and improving overall product quality. Moreover, starch can withstand a wide range of processing conditions, including heat, acidity, and shear forces, making it suitable for diverse food applications such as sauces, soups, dairy products, and baked products. Additionally, starches can be modified through various processes, as mentioned in the above methods, to tailor their functionality according to specific formulation requirements, further expanding their utility in food stabilization. With its natural origin, cost-effectiveness, and multifunctional properties, starch remains a cornerstone ingredient in the pursuit of food stability and quality (Jo and Shi 2024; Lee and Kang 2024; Wang et al. 2016).
For instance, adding modified starch granules to oil-in-water emulsions as particle stabilizers showed that oil-in-water emulsions stabilized by hydrophobic starch particulates demonstrated remarkable stability. The emulsions had a droplet size ranging from 1 to 20 µm and exhibited significant creaming but remained stable to coalescence over several months. Notably, starch particulates generated from chemically cross-linked granules, treated with octenyl succinic anhydride, and reduced in size via freezer milling, acted as effective stabilizers. These starch particulates, modified to a degree of substitution of approximately 0.03, prevented significant changes in droplet size distributions for over three months (Yusoff and Murray 2011). Additionally, surface tension measurements confirmed the supposition that the emulsions were stabilized by starch particulates rather than soluble starch molecules. Hydrophobic modification of starch granules with octenyl succinic anhydride enhances their emulsifying properties. By becoming partially hydrophobic, these starch granules act as particle stabilizers in oil-in-water emulsions, effectively adsorbing at the oil–water interface to stabilize the emulsion. This stabilization mechanism is typical of Pickering emulsions, where solid particles, rather than surfactants, stabilize the droplets. The modified starch granules facilitate this by providing a barrier to coalescence, contributing to the long-term stability of the emulsion without significant changes in droplet size (Yusoff and Murray 2011).
Furthermore, the effects of adding potato starch to yogurt at various including 0.25%, 0.5%, 0.75%, and 1%, were tested against a control (no stabilizer) and a gelatin standard 0.6%. The results reported that higher concentrations of starch, including 0.75% and 1%, effectively minimized increases in total acidity and reductions in pH. Whereas yogurts with 0.75% and 1% starch maintained lower acidity levels, with mean values around 1.35% and 1.33%, respectively, compared to the control. This suggests that the starch helped maintain a more stable acidic environment in the yogurt during storage. Starch additions significantly reduced syneresis, indicating better water retention (Altemimi 2018). This effect was more pronounced at higher starch concentrations, with 1% starch showing the least whey separation. Starch addition also impacted microbial growth. Yogurts with starch showed lower total bacteria counts compared to the control, enhancing microbial stability over the 15-day storage period at 5 °C. Besides, the higher starch concentrations generally performed better in sensory assessments, suggesting an improvement in overall yogurt quality. The addition of starch enhances the yogurt's textural stability by improving the viscosity and gel strength, which helps retain moisture and reduces syneresis. Starch also seems to create a less favorable environment for microbial growth, possibly due to the altered structure reducing the availability of free water. Sensory improvements are likely due to the smoother texture and consistent flavor profile maintained by the starch throughout storage (Altemimi 2018).
Additionally, the study by Zhao et al. (2019) investigates high internal phase water-in-oil emulsions stabilized by food-grade starch, aiming to enhance emulsion stability and water content with eco-friendly materials. Emulsions showed gel-like behaviors at high water contents 95% by weight with a significant increase in both storage and loss modulus when starch was included, where storage values increased substantially, from about 80 to 180 pascals, and loss modulus from about 3 to 10 pascals with just 0.3% starch added, highlighting the starch's effectiveness at reinforcing the emulsion structure. Besides, confocal laser scanning microscopy revealed that with increasing water content, the morphology of the droplets transitioned from spherical to non-spherical, suggesting a decrease in interfacial tension, where this morphological change supports the formation of a stable high internal phase emulsion (Zhao et al. 2019). Scanning electron cryomicroscopy images showed polyhedral droplets, with starch primarily located in the water phase, reinforcing the role of starch in stabilizing these structures by enhancing the viscoelastic properties of the emulsion. The presence of food-grade starch enhances the viscoelastic properties of the emulsion, which are crucial for maintaining stability and structural integrity, especially at high water contents. The starch effectively increases the viscosity and modulus of the emulsion, contributing to its stability by forming a robust network that resists deformation and coalescence. This mechanism is vital for applications where long-term stability of emulsions is required, such as in food and cosmetic products. The findings indicate that even a small addition of starch significantly impacts the rheological properties and microstructure of the emulsion, providing a cost-effective and environmentally friendly alternative to synthetic stabilizers (Zhao et al. 2019).
Moreover, the physicochemical properties and sensory attributes of Greek-style yogurt were explored after the addition of retrograded corn starch containing 27% and 70% amylose. The results showed that yogurt enriched with retrograded starch containing 70% amylose displayed almost triple the resistant starch content compared to retrograded starch containing 27% amylose, contributing to potential prebiotic benefits. Specifically, resistant starch content ranged from 1.74 to 2.32 g per 100 g for starch containing 27% amylase and 3.5 to 4.21 g per 100 g for starch containing 27% amylase. Adding retrograded starch significantly reduced syneresis, enhancing the yogurt's water-holding capacity and texture. Besides, adding 27% and 70% amylose decreased syneresis more effectively compared to control samples, with 70% showing a more pronounced effect. The inclusion of retrograded starch increased the consistency and firmness of the yogurt (Cota-López et al. 2023). This improvement was noted as a direct correlation with the amylose content of the starch used. The increased amylose content to 70% likely contributed to the higher resistant starch content, as amylose is more resistant to digestion and can form more stable gel structures. This stability translates into reduced syneresis and improved textural properties. The sensory analysis showed that yogurts with added retrograded starch, especially at a concentration of 12.5 g per 100 g, were well-received in terms of general acceptance, appearance, and flavor. There was no significant difference in the overall acceptance of starch-containing 27% amylase-added yogurt compared to the control, while starch-containing 70% amylase-added samples showed slightly lower scores, though still within acceptable ranges. The improved texture and consistency due to retrograded starch addition likely contributed to the positive sensory feedback. Although higher concentrations of retrograded starch could potentially influence flavor and mouthfeel, the study's results suggest that the chosen concentrations managed to enhance the yogurt's overall quality without compromising its sensory appeal (Cota-López et al. 2023).
Furthermore, the incorporation of heat–moisture-treated rice starches as stabilizers in nonfat yogurt significantly improved the physicochemical and sensory properties of the yogurt, where the nonfat yogurt stabilized with 1.0% heat–moisture-treated rice starch showed a whey separation rate of only about 12%, compared to nearly 24% in the control yogurt without starch. This substantial decrease highlights the effective stabilization provided by the heat–moisture-treated starch (Lee and Kang 2024). Besides, there was a 2.8-fold increase in yogurt viscosity, demonstrating the effectiveness of heat–moisture-treated rice starch in enhancing texture, as well as yogurt enriched with heat–moisture-treated starch also exhibited a higher total solids content, indicating less syneresis and improved consistency. The nonfat yogurt containing 1.0% heat–moisture-treated starch with high amylose content and 15% moisture exhibited a viscosity of approximately 4.50-Pa seconds, representing a significant increase from the control. This improved viscosity indicates a better texture, which is essential for consumer satisfaction in yogurt products. The increase in viscosity and reduction in whey separation is primarily due to the interaction between the starch granules and the yogurt matrix. The heat–moisture-treated process alters the starch structure, making it less prone to enzymatic breakdown and more effective at water retention. This interaction helps in forming a more stable and cohesive gel network, which reduces syneresis (whey separation) and improves the textural quality of the yogurt (Lee and Kang 2024).
In summary, starch is invaluable in food formulation due to its ability to modify viscosity, enhance texture, and prolong shelf life, serving as a stabilizer that forms a gel-like structure to thicken and stabilize food products. It can withstand a variety of processing conditions and is modified to tailor its functionality for specific needs, making it essential for high-quality food products like sauces, soups, and dairy items. Additionally, modified starches are used as stabilizers in food emulsions and yogurts, where they improve texture, prevent ingredient separation, and enhance product stability by interacting with water molecules and other ingredients, thus maintaining quality and consistency over time.
Plant-based meat replacers
Extensive research over recent decades has explored the application of starch in meat products, utilizing starch as a filler in comminuted products such as sausages and meat patties. As a non-meat ingredient, starch acts effectively in water binding and serves as a volumizing agent, enhancing the bulk of meat products. Pre-gelatinized starch improves water absorption at lower temperatures, mitigating water loss during the cooking of meat. This water-binding capacity of starch also facilitates a reduction in caloric content in products such as sausages. Starch helps maintain sensory and textural qualities, for instance, by augmenting firmness and enhancing the structure when animal fats are substituted with vegetable oils, which improves the lipid profile by increasing unsaturated fat content. Additionally, starch incorporation into meat emulsions has been observed to create a denser and stronger heat-induced protein matrix. The benefits of using starch include its cost-effectiveness and the ability to finely tune functional attributes, including cold swelling capacity, water solubility, and rheological characteristics through various modifications (Bühler et al. 2022; Chen et al. 2022; Das et al. 2015; Dobson et al. 2022).
The authors evaluated the impact of plant starches, including sorghum flour, finger millet flour, and carrageenan, as fat substitutes in chicken patties on various parameters. They revealed significant reductions in fat content with adding 10.50% of sorghum flour, 9.42% of finger millet flour, and 9.68% of carrageenan, as well as cholesterol levels decreased with adding sorghum flour at 142.63 mg per 100 g patties, finger millet flour at 140.90 mg per 100 g patties, carrageenan at 127.03 mg per 100 g patties compared to the control that exhibited 17.25% fat and 209.14 mg cholesterol per 100 g patties (Das et al. 2015). While there was no significant difference in pH, water holding capacity, and protein content among the treatments, the sensory analysis indicated no significant differences in terms of appearance, flavor, juiciness, texture, and overall acceptability between the control and treated patties. Regarding the effects of plant starches and carrageenan, the article explains that these ingredients, due to their water-binding capabilities and textural properties, serve as effective fat substitutes in meat products. Sorghum and finger millet flours, by adding bulk and assisting in moisture retention, contribute to the textural integrity and sensory quality of low-fat patties. Carrageenan, recognized for its ability to form stable gels, helps in improving the juiciness and consistency of the patties, maintaining a desirable texture and flavor profile like higher-fat counterparts. These substitutions not only reduce fat content and potentially caloric intake but also maintain consumer-acceptable sensory characteristics, which are crucial for the marketability of healthier meat product options (Das et al. 2015).
Moreover, the effects of exogenous wheat starch on the formation of fibrous structures in peanut protein during high-moisture extrusion were examined. The results indicated several key changes to the textural properties of the extrudates, where wheat starch was added at concentrations ranging from 0 to 8%, and the fibrous degree decreased gradually and significantly with increasing wheat starch content, indicating a negative effect on the orientation of the fibrous structure. Specifically, the lengthwise shear force increased significantly with higher wheat starch content, indicating that higher amounts of wheat starch strengthen the longitudinal structure of the extrudate. Additionally, the addition of 2% wheat starch resulted in notable changes in the textural properties of fibrous, where the hardness decreased significantly with an increase in wheat starch content, suggesting that wheat starch reduces the compactness of the protein network, leading to a softer texture. Besides, the springiness and chewiness showed no significant change at 2%, 4%, and 8% wheat starch, indicating that wheat starch did not affect the elasticity and chewiness of the extrudate as much as other properties (Zhang et al. 2020a).
From a molecular perspective, wheat starch promotes the aggregation of protein molecules primarily by disrupting intramolecular disulfide bonds, enhancing hydrophobic interactions, and increasing the apparent viscosity, which helps to stabilize the newly formed conformation during the extrusion process. This was observed with a significant reduction in the thermal stability of the protein, evidenced by a decrease in the peak thermal transition temperature and changes in the enthalpy of conarachin and arachin, the major proteins in peanut protein powder. Moreover, wheat starch influenced the microstructural formation during extrusion. In the die and cooling zones, the presence of wheat starch led to the formation of larger, loosely structured gels, which contributed to the less aligned and weaker fibrous structure observed in the final extrudate. This structural modification due to wheat starch addition was crucial for determining the textural attributes of the high moisture extruded products (Zhang et al. 2020a).
Furthermore, adding amylopectin during high-moisture extruded texturization toward plant-based meat substitute applications increased the tensile strength of the protein matrix, making it more resilient under strain. Besides, amylopectin additions led to a significant increase in water-holding capacity compared to amylose, which is crucial for maintaining the juiciness and texture of plant-based meat substitutes. Amylopectin also reduces the mixture’s viscosity, which is beneficial during the extrusion process as it allows the protein chains to align more effectively, promoting the formation of fibrous structures (Chen et al. 2022). In contrast, amylose increased viscosity, leading to a more challenging extrusion process. Amylopectin facilitates the unfolding of protein structures during the extrusion, which is critical for the alignment of these structures into a fibrous texture that mimics meat. The study indicated that amylopectin's impact on reducing viscosity is key here, as lower viscosity allows for better movement and alignment of protein chains. Amylose's tendency to undergo phase separation with proteins was shown to create a more rigid and less aligned structure. This phase separation leads to distinct layers within the extruded product, which can adversely affect the texture by preventing the formation of a continuous fibrous network. Amylopectin's ability to interact more effectively with water also aids in the texture formation of the final product. By maintaining a hydrated environment, amylopectin ensures that the protein matrix does not dry out, which is crucial for achieving a tender and juicy texture in meat analogs (Chen et al. 2022).
Additionally, the particle-filled protein–starch composites as the basis for plant-based meat analogs were studied by Dobson et al. (2022), where tensile strength reached up to 4.5 megapascals, indicating robustness, while elongation at break extended to 80%, suggesting flexibility. These values demonstrate the enhanced structural integrity and resilience of the composites, crucial for maintaining shape and texture during processing and consumption. The composites exhibited a notable water-holding capacity of 0.68 g of water per gram of dry material and an oil-holding capacity of 0.53 g of oil per gram of dry material, highlighting their ability to retain moisture and fats, key factors in replicating the juiciness and mouthfeel of meat. Starch particles ranging from 1 to 10 µm were utilized, indicating the importance of particle size in influencing the composite's mechanical and textural properties. Smaller particles may offer a greater surface area for interaction with proteins, leading to improved reinforcement and texture enhancement. The synergistic interaction between protein and starch particles. The dispersion of starch within the protein matrix reinforces the structure, imparting strength and flexibility to the composite. This reinforcement is essential for mimicking the fibrous texture of meat and ensuring the integrity of the product during processing and cooking. Furthermore, the water and oil-holding capacities contribute to the succulence and mouthfeel of the analog, enhancing its sensory appeal to consumers. Overall, the findings underscore the potential of particle-filled protein–starch composites as promising candidates for the development of high-quality plant-based meat alternatives (Dobson et al. 2022).
To summarize, starch plays a vital role in meat product formulation, acting as a filler to enhance texture and reduce caloric content. Its pre-gelatinized form aids water absorption, minimizing moisture loss during cooking. Starch also improves sensory qualities when substituting animal fats with vegetable oils, maintaining product consistency. Meanwhile, plant starches and carrageenan serve as effective fat substitutes in chicken patties, reducing fat content and cholesterol levels while maintaining sensory acceptability. Wheat starch influences textural properties in protein extrusion, altering protein structure and enhancing water-holding capacity. Additionally, amylopectin in plant-based meat substitutes enhances tensile strength and water retention, which is crucial for mimicking meat textures and improving consumer appeal. Particle-filled protein–starch composites exhibit robust mechanical properties and high water/oil-holding capacities, demonstrating potential as high-quality plant-based meat alternatives.
Three-dimensional food printing
Three-dimensional printing is an advanced manufacturing technique utilizing digital models and diverse materials to fabricate products. Applied to food production, three-dimensional printing merges digital cooking methods, shaping food items with precision and efficiency. This technology offers a user-friendly interface and adaptable design, ensuring high-quality output at affordable costs. With potential applications in personalized food design, small-scale production, and tailored nutrition, three-dimensional printing serves diverse consumer groups, including the elderly with swallowing difficulties, pregnant women, children, athletes, and others (Rashwan et al. 2023b; Zhang et al. 2022b). To make high-quality three-dimensional printed foods, edible materials called bio-inks with the right texture and taste are required. Starch, which is a key source of energy in the human diet, is often used in food processing (Chen et al. 2024). Furthermore, starches show promise as a three-dimensional printing ink due to their ability to form films and their pseudoplastic and viscoelastic properties. Its excellent shear stability and viscosity make it suitable for maintaining stability in three-dimensional printed food structures. Interactions between starch molecules play a crucial role in forming deposited structures, particularly at higher starch concentrations. These attributes suggest that starch could serve effectively as three-dimensional printing ink, and this review provides an overview of recent research on various types of starch-based materials used in three-dimensional food printing, emphasizing their applications (Ahmadzadeh and Ubeyitogullari 2022; Feng et al. 2019; González et al. 2022; Wu et al. 2023).
The effect of post-processing treatments, including blanching, steaming, microwaving, shallow frying, and deep frying, on the quality of three-dimensional printed rice starch constructs was explored, where deep-fried constructs exhibited the least cooking loss at 0.73%, indicating minimal moisture loss compared to other methods. The hardness of these constructs was significantly high at 1708.59 g, the highest among all treatments, suggesting better structural integrity and reduced susceptibility to mechanical damage during handling. The study utilized principal component analysis to evaluate various factors, including dimensional stability and identified deep frying as the method providing the best dimensional stability due to the rigidity imparted by the frying process. Both deep frying and shallow frying were noted to offer better shape fidelity, suggesting that constructs maintained their designed shapes well post-treatment, attributed to the quick crust formation that supports the structure (Theagarajan et al. 2021). The void fraction and porosity were examined, revealing that methods involving dry heat and high temperatures generally led to constructs with increased porosity and voids, due to moisture loss and material contraction. Various post-processing methods impacted the quality of three-dimensional printed rice starch constructs through different physical and chemical interactions; for example, deep frying provided rapid cooking and crust formation, preserving shape and increasing hardness. This method resulted in constructs with the best sensory profiles, indicating higher consumer acceptability, whereas steaming and blanching generally produced softer constructs with higher cooking losses, and microwaving resulted in significant hardness but less uniformity in texture and structure due to uneven heating (Schwab et al. 2020; Theagarajan et al. 2021).
Furthermore, the addition of catechin and procyanidin significantly changed the rheological properties of rice starch gel, notably increasing viscosity by 20% compared to the control group. Assessment of printability via parameters like extrusion force and filament diameter revealed reduced force requirements, with a 15% decrease in extrusion force with catechin, facilitating smoother printing. Filament diameter measurements showed a 10% decrease with catechin, indicating improved print resolution. Mechanical property evaluations, focusing on tensile strength and Young's modulus, demonstrated enhancements with catechin and procyanidin, with a 25% increase in tensile strength, suggesting better structural integrity. These improvements in printability and mechanical properties are attributed to interactions between catechin/procyanidin and rice starch molecules, increasing viscosity and facilitating better flow behavior, resulting in smoother printing and finer details. Additionally, catechin and procyanidin act as reinforcing agents, strengthening intermolecular interactions within the constructs and enhancing overall performance (Zeng et al. 2021).
Additionally, starch-derived gels are utilized in three-dimensional printing for creating food items. The study examined the effects of varying concentrations of sodium alginate and xanthan gum on the rheological and three-dimensional printing properties of potato starch composite gels. The optimal concentration for both additives was found to be 2.5% weight/weight, achieving the best geometric accuracy (exceeding 95%) and demonstrating high shape retention. The viscosity of the starch gel increased significantly upon the addition of these agents, supporting excellent extrudability and structural integrity in three-dimensional printing applications. The gels displayed pseudoplastic behavior, where higher concentrations of sodium alginate and xanthan gum corresponded to increased apparent viscosity and storage modulus, indicating improved printability and mechanical stability (Cui et al. 2022). The improved rheological properties due to the addition of sodium alginate and xanthan gum can be attributed to their role in enhancing the viscoelasticity of the starch composite gel. The study found that these additives increased the gel’s resistance to deformation under stress (higher storage modulus) and its ability to recover its original shape after deformation (loss modulus). This behavior is crucial for three-dimensional printing, where the material must maintain its shape post-extrusion. Additionally, the presence of these additives helps in controlling the flow behavior of the gel during printing, ensuring that the material is sufficiently fluid for extrusion but quickly regains rigidity to maintain the integrity of the printed structure. The findings suggest that the synergetic effect of the combined use of sodium alginate and xanthan gum significantly improves the printability and structural fidelity of three-dimensional printed starch-based products (Cui et al. 2022; He et al. 2020b; Wedamulla et al. 2023).
The authors studied the effect of hot extrusion three-dimensional printing on starch digestibility by manipulating starch–lipid interactions with glycerol monostearate and stearic acid. They found that hot extrusion three-dimensional printing facilitated the formation of V-type starch–lipid complexes, which enhanced resistance to enzymatic hydrolysis. The study revealed that slowly digestible starch and resistant starch contents were significantly higher with stearic acid, reaching 25.06% resistant starch at 10% stearic acid addition, compared to lower values with glycerol monostearate. This indicates that stearic acid's linear hydrophobic chains are more effective at interacting with starch to form ordered structures, leading to increased starch resistance (Liu et al. 2022). The improved rheological properties observed in the starch–lipid mixtures are primarily due to the formation of more structured and stable complexes during the hot extrusion three-dimensional printing process. The formation of V-type starch–lipid complexes under thermal and shear stresses results in a gel with enhanced viscosity and elasticity, critical for successful three-dimensional printing. These complexes exhibit increased resistance to enzymatic breakdown, thereby controlling the digestibility of starch. The process also enhances the structural integrity and print fidelity of the starch-based materials, which is crucial for maintaining desired shapes and textures in three-dimensional printed food products (He et al. 2020a; Liu et al. 2022).
Moreover, the three-dimensional printed starch structures were tested under compression to mimic oral processing conditions. The findings indicated that the yielding point, where the structures began to collapse under pressure, varied depending on the internal structure and the amount of hydration. Structures with more pores yielded at lower pressures due to faster internal hydration, which facilitated quicker breakage and increased surface area in contact with the liquid. Besides, the dispersion of starch increased significantly after the structures yielded and broke down. This increase in dispersion was influenced by the structure's pore size and distribution. Structures with larger or more numerous pores showed a higher rate of starch dispersion upon hydration and mechanical pressure, emphasizing the role of internal architecture in controlling food texture during consumption. In addition, the hydration of starch prints led to significant changes in mechanical properties. The study showed that food structures with higher initial surface area exposed to the liquid exhibited lower yielding points, likely due to faster hydration. This result supports the potential of three-dimensional food printing to tailor food products that can quickly soften in the mouth, improving the ease of swallowing and digestion (Bugarin-Castillo et al. 2023).
In conclusion, the integration of three-dimensional printing into food production offers precise control over food structure and texture, catering to diverse consumer needs such as personalized nutrition and enhanced sensory experiences. Utilizing starch-based bio-inks, the technology demonstrates promise in creating food items with tailored properties, including improved printability, mechanical strength, and resistance to enzymatic breakdown, crucial for maintaining shape and texture during processing and consumption. Furthermore, the study's exploration of post-processing methods and their impact on the quality of printed food elucidates strategies for optimizing structural integrity and sensory attributes, paving the way for the development of innovative and appealing food products suitable for various dietary requirements and preferences.
Prebiotics
Since the role of intestinal microbiota in metabolism was understood, the importance of prebiotics, such as fibers, which affect microbiota modulation, has been growing day by day. Prebiotics are non-digestible ingredients used to encourage the viability and growth of probiotic bacteria in the gastrointestinal tract. Many studies indicated that resistant starch is considered an effective prebiotic source when it is naturally or chemically made resistant to digestion, leading to the maintenance of a healthy intestinal environment and mitigating associated chronic diseases (Abdelshafy et al. 2022; Abdelshafy et al. 2024; Gibson et al. 2017; Park et al. 2024b; Tekin and Dincer 2023; Thompson et al. 2022). Resistant starch, characterized by its inability to be fully digested in the small intestine, serves as a valuable prebiotic due to resistant starch's capacity to selectively stimulate the growth and activity of beneficial gut bacteria. As resistant starch reaches the colon undigested, resistant starch acts as a substrate for fermentation by gut microbiota, leading to the production of short-chain fatty acids such as acetate, propionate, and butyrate. These short-chain fatty acids play crucial roles in maintaining gut health by promoting the proliferation of beneficial bacteria, regulating immune function, and improving gut barrier integrity. Additionally, resistant starch has been associated with various health benefits, including improved insulin sensitivity, reduced inflammation, and enhanced satiety, highlighting its potential as a functional ingredient in promoting overall well-being through gut microbiota modulation (Fig. 8). Therefore, resistant starch is meeting the International Scientific Association for Probiotics and Prebiotics consensus criteria for the definition of a prebiotic (Bush et al. 2023; Gibson et al. 2017).
Effects of resistant starch on the human body, starting from its consumption. Resistant starch, typically consumed as a supplement, undergoes fermentation in the colon, which leads to the production of gases and a reduction in the starch's energy value. This fermentation process generates short-chain fatty acids (SCFAs), which confer several health benefits. These SCFAs are beneficial for the cells lining the intestines and positively impact glucose and lipid metabolism. Overall, the diagram highlights how resistant starch promotes gut health and metabolic functions
For example, the proliferative and protective effect of the resistant starch prepared from Solanum tuberosum on the viability of probiotics in fermented milk during refrigeration storage was studied. The fermented milk supplemented with resistant starch at a concentration of 25 mg per milliliter showed higher viability of probiotics compared to the fermented milk without resistant starch. Lactobacillus paracasei CD4, Lactobacillus gastricus BTM7, Brevibacillus aydinogluensis BTM9, Lactobacillus rhamnosus GG, and Lactobacillus fermentum K75 recorded 9.38, 8.30, 6.39, 6.30, and 6.77 logarithm base 10 colony-forming units per milliliter, respectively in the fermented milk supplemented with resistant starch, while they recorded 7.30, 8.07, 6.27, 6.60, and 6.00 logarithm base 10 colony-forming units per milliliter, respectively in the control sample after the fermentation process. Additionally, the resistant starch contributed to maintaining the probiotic viability in the fermented milk during refrigeration storage for 21 days (Chakravarty et al. 2021). The prebiotic effect of potato-resistant starch was studied using in vitro simulated gut fermentation. After fermentation for 24 h, the intestinal microbial composition was significantly changed by resistant starch. The Firmicutes/Bacteroidetes ratio significantly decreased, while the Bifidobacterium, Megamonas, and Prevotella significantly increased. Besides, the higher levels of acetate 138.34 micromoles, propionate 41.45 micromoles, and butyrate 21.65 micromoles were recorded by resistant starch. The resistant starch played a key role in promoting intestinal health and improving the probiotic functions (Liang et al. 2021).
Moreover, the influence of corn-resistant starch prepared by microwave heat, debranching, and autoclave on the rheology, structure, and viable count of set yogurt was studied. The yogurt supplemented with the microwave-heated resistant starch showed the highest lactic acid bacteria count, followed by yogurt supplemented with debranched, and autoclaved resistant starch. The microwave-heated resistant starch is a favorable supplement to improve the microstructure and rheological properties and accelerate the fermentation process of yogurt (Jia et al. 2022). Besides, supplementation of food with resistant starch beneficially modulates the gut microbes with a decrease in inflammation and gut leakiness, indicating a resistant starch prebiotic effect for nutritional applications and functional foods (Kadyan et al. 2023). The resistant starch of potato showed a significant prebiotic effect when consumed at a dose of 3.5 g/day for 28 days, stimulating an increase in probiotics, including Bifidobacterium and Akkermansia, and reducing diarrhea and constipation-associated bowel. Resistant starch is safe and well tolerated at 3.5 to 7 g/day (Bush et al. 2023).
Furthermore, the jackfruit seed starch was modified to resistant starch type III using a retrogradation process, resulting in a significant increase in resistant starch content from 17.63 to 30.21%, and in vitro fermentation studies revealed that resistant starch type III promoted the growth of beneficial gut bacteria, with a notable increase in Bifidobacterium population compared to untreated jackfruit seed as a control sample. In addition, in an animal model of diabetes, resistant starch type III supplementation led to a significant reduction in fasting blood glucose levels compared to the diabetic control group, indicating its potential therapeutic effect on diabetes management (Vu et al. 2024). The increase in resistant starch content through retrogradation enhances the fermentability of jackfruit seed starch in the colon, promoting the growth of beneficial bacteria like Bifidobacterium. This prebiotic effect is crucial in diabetes management as it contributes to improved gut health and metabolic function. The observed reduction in fasting blood glucose levels further supports the potential of resistant starch type III as a dietary intervention for controlling blood sugar levels in individuals with diabetes. Overall, the results highlight the promising role of resistant starch type III from jackfruit seed starch as a natural prebiotic for diabetes treatment, offering potential benefits for gut health and glucose regulation (Vu et al. 2024).
Additionally, resistant starch-enriched brown rice showed a higher yield of insoluble fraction in the digestive process compared to white and brown rice. Particularly, the total digestible starch content decreased during digestion, while resistant starch content significantly increased. For example, in the large intestine, the resistant starch content of resistant starch-enriched brown rice was notably higher compared to that of white and brown rice. Besides, resistant starch-enriched brown rice consumption led to an increase in beneficial gut bacteria such as Bifidobacteria (Park et al. 2024b). This was accompanied by enhanced production of short-chain fatty acids such as acetate, propionate, and butyrate, critical for maintaining gut barrier integrity and promoting health. In addition, resistant starch-enriched brown rice was more effective than the positive control (fructooligosaccharides) in promoting the growth of probiotic strains, including Lactobacillus and Bifidobacterium, indicating strong prebiotic potential. The increase in resistant starch content during digestion suggests that resistant starch-enriched brown rice is less susceptible to breakdown by digestive enzymes, thus reaching the colon, where it serves as a fermentable substrate for beneficial microbes. This fermentation process produces short-chain fatty acids, which play essential roles in enhancing gut health, such as reducing inflammation, strengthening the gut barrier, and providing energy sources for colonic cells (Park et al. 2024b).
In summary, the importance of prebiotics like resistant starch in modulating intestinal microbiota and promoting gut health has gained significant attention, with studies demonstrating their ability to selectively stimulate beneficial gut bacteria and produce short-chain fatty acids. Research indicates that resistant starch, whether derived from sources like potatoes or jackfruit seeds or enriched in brown rice, effectively promotes the growth of probiotics, and enhances gut barrier integrity, offering potential therapeutic effects for managing conditions like diabetes and improving overall well-being. These findings underscore the valuable role of resistant starch as a natural prebiotic, capable of positively influencing gut microbial composition and metabolic function, thereby advocating its inclusion in functional foods for nutritional and health benefits.
Encapsulation systems
Nanotechnology is a wide-ranging field that includes using regular device physics in new ways, creating materials on a very small scale, and trying to control things down to the level of individual atoms. This idea has lots of uses in science, like making eco-friendly materials and better ways to deliver drugs. Lately, scientists have been interested in making tiny, biodegradable crystals and particles, especially using starch, which is something new (Ahmad et al. 2020a; Osman et al. 2024; Rashwan et al. 2024; Shabana et al. 2019). Starch is a highly studied natural polymer that is eco-friendly, inexpensive, biodegradable, and can be heated and molded (thermoplastic). It is a promising option for making non-toxic tiny crystals or particles (nanocrystals/nanoparticles) to use as fillers in plastic materials (Estevez-Areco et al. 2020; Maniglia et al. 2021). Furthermore, starch has the potential to serve as a cost-effective alternative to high-priced encapsulating agents as a wall material in microcapsule production. Starch-derived nanoparticles exhibit distinctive characteristics, including regulated release, enhanced solubility in water, increased bioavailability, and enhanced transportation of active compounds in both food products and the human organism (Moura et al. 2021; Oh et al. 2020).
For instance, the synthesis and characterization of piperine-loaded starch nanoparticles demonstrated successful encapsulation with starch nanoparticles, enhancing piperine's aqueous solubility. Optimal conditions yielded a maximum piperine loading capacity of 4.74 mg per milligram. Particle sizes ranged from 52 to 154 nm with an average diameter of 88 nm. The surfactant Span 60 significantly influenced the loading capacity, achieving the highest at 2.268 mg per milligram with a concentration of 0.3 mg per milliliter. Piperine release from the nanoparticles was sustained over 168 h, closely correlating with the swelling behavior of the nanoparticles (Chong et al. 2020). Approximately 94.6% of piperine was released at a swelling ratio of 4.5 g per gram, showing a promising controlled release profile. Piperine-loaded starch nanoparticles were synthesized using an in situ nanoprecipitation method. This method involved dissolving starch in a sodium hydroxide: urea aqueous solution, followed by mixing with a piperine–ethanol solution containing a surfactant. This mixture was then subjected to nanoprecipitation to form starch nanoparticles encapsulating piperine. The surfactants used especially Span 60, played a critical role by enhancing the hydrophobic interactions that increased the piperine loading capacity. The study found that the nanoparticles were predominantly spherical, providing a high surface area that facilitated better piperine encapsulation and release (Chong et al. 2020).
Additionally, the production of tapioca starch nanoparticles by nanoprecipitation–sonication treatment was investigated by Hedayati et al. (2020), where they revealed that incorporating sonication in the nanoprecipitation process using acetone to produce tapioca starch nanoparticles not only reduced the acetone usage but also increased the yield. Particle size analysis indicated that nanoparticles ranged from 163 to 451 nm, increasing with the starch concentration used in the synthesis. The lowest crystallinity was reported for tapioca starch nanoparticles produced with one gram of starch at 6.49%, showcasing a significant reduction compared to native starch, which had a crystallinity of 25.12%. Scanning electron microscopy and transmission electron microscopy imaging confirmed that tapioca starch nanoparticles were spherical and uniformly shaped across different concentrations (Hedayati et al. 2020). Besides, the synthesis of starch nanoparticles from horse chestnut, water chestnut, and lotus stems using mild alkali hydrolysis and ultrasonication was successful. The average particle sizes were 420.33 nm for horse chestnut, 606.31 nm for lotus stem, and 535.21 nm for water chestnut. The zeta potential indicated stability differences, with water chestnut showing the highest negative potential at -41.29 millivolts. Both water absorption capacity and antioxidant properties of starch nanoparticles increased compared to native starch, while oil absorption capacity decreased. Scanning electron microscopy imaging revealed disrupted granular structures, and X-ray diffraction analysis confirmed a reduction in crystallinity post-treatment, suggesting more amorphous structures (Ahmad et al. 2020b).
Another study successfully extracted starch nanoparticles from potato peel waste using a simple alkali extraction and ultrasonic treatment, achieving a yield of about 45%. The starch nanoparticles exhibited an average size of 50 nm with regular spherical shapes and demonstrated high stability in aqueous solutions with a zeta potential of −20.60 millivolts. The alkali treatment partially dissolves the starch granules, making them more susceptible to fragmentation under the mechanical forces introduced during sonication. This process not only reduces the particle size of starch but also enhances its reactivity by increasing the surface area. In addition, X-ray diffraction analysis indicated a B-type crystal structure with an average crystallite size of 17.26 nm. Scanning electron microscopy and transmission electron microscopy analyses confirmed the nanoparticles' spherical morphology and semicrystalline structure. The antioxidant activity tests showed increasing activity with higher starch nanoparticle concentrations (Hasanin 2021).
Moreover, the encapsulation of rutin, a polyphenol with therapeutic potential, using quinoa and maize starch nanoparticles was explored, where quinoa-derived starch nanoparticles demonstrated an average particle size of 107 nm, encapsulation efficiency of 67.4% and loading efficiency of 26.6%. Maize-derived starch nanoparticles showed an average particle size of 222 nm, encapsulation efficiency of 63.1%, and loading efficiency of 22.7%. Both types of starch nanoparticles exhibited a zeta potential of approximately -18 millivolts. In vitro, digestion tests indicated improved bioavailability of rutin, with quinoa-derived starch nanoparticles showing higher antioxidant activities than maize-derived starch nanoparticles (Remanan and Zhu 2021).
Ultrasonication enhances the mechanical disruption of starch granules, aiding the integration of rutin into the starch matrix. The encapsulation efficiencies were attributed to the specific interactions between rutin and the starch molecules. For quinoa starch, the small particle size and high surface area likely enhanced its encapsulation efficiency and loading efficiency compared to maize starch (Remanan and Zhu 2021). Additionally, the preparation and characterization of quinoa starch nanoparticles as carriers for quercetin was optimized using a nanoprecipitation method, where optimal conditions achieved the smallest particle size of 162.3 nm and polymer dispersity index of 0.43, showing significant improvements in loading and stability of quercetin. The loading efficiency of quercetin on quinoa starch nanoparticles was 26.62%, compared to 17.57% on maize starch nanoparticles, indicating superior capacity. Enhanced bioactivity of quercetin was maintained due to this efficient encapsulation, and stability tests indicated that quinoa starch nanoparticles protected the bioactivity of quercetin effectively over time. Besides, starch nanoparticles bonded with quercetin via hydrogen interactions, leading to the disappearance of V-type crystalline structures and an increase in their overall crystallinity upon quercetin integration (Jiang et al. 2022).
Another study developed a green method to produce debranched starch nanoparticles with varying crystalline structures via electrostatic spraying into different ethanol concentrations, where the results showed that debranched starch nanoparticles were successfully synthesized with diameters ranging from 243 to 337 nm. The particle size and distribution were controlled by adjusting the ethanol concentration in the electrostatic spraying process, leading to varied nanoparticle sizes and structures depending on the solvent concentration. The study observed distinct crystalline structures in debranched starch nanoparticles based on the ethanol concentration used during preparation (Lin et al. 2022). In addition, debranched starch nanoparticles prepared in 60% ethanol exhibited an A-type crystalline structure, while those in 80% ethanol showed a combined A + V-type structure, and in absolute ethanol, the nanoparticles were amorphous. The nanoparticles displayed good monodispersity, with polydispersity index values ranging from 0.20 to 0.32. This high monodispersity, coupled with effective dispersion, was attributed to the electrostatic spraying process, which prevented aggregation by ensuring that all starch molecules in the solution carried the same charge, repelling each other. The electrostatic spraying method allowed for the fine-tuning of nanoparticle properties, such as size and crystallinity, by adjusting operational parameters like solution concentration, flow rate, voltage, and distance from the collector. This method facilitated the production of well-dispersed and stable nanoparticles. Thermogravimetric analysis results demonstrated that the thermal stability of debranched starch nanoparticles varied with their crystalline structure and ethanol concentration during preparation. Debranched starch nanoparticles prepared in 60% ethanol showed the highest thermal degradation temperature, suggesting a more orderly and tightly packed molecular arrangement compared to debranched starch nanoparticles prepared in absolute ethanol, which were more amorphous and degraded at lower temperatures (Lin et al. 2022).
To summarize, nanotechnology in the field of starch-based materials is making significant strides, particularly in the synthesis of biodegradable nanocrystals and nanoparticles that are eco-friendly, cost-effective, and offer enhanced functionality in drug delivery and material engineering. Starch, a naturally abundant and thermoplastic polymer, is proving to be an exceptional resource for creating non-toxic nanocrystals and nanoparticles, suitable as plastic fillers, and microencapsulation agents. Innovations such as piperine-loaded starch nanoparticles and quinoa starch nanoparticles for quercetin delivery exemplify advancements in achieving controlled release, increased solubility, and improved bioavailability, showcasing the potential of starch derivatives in diverse applications from food products to pharmaceuticals.
Bioplastics and edible films
Polymeric materials derived from petroleum have historically prevailed in the packaging sector owing to their cost-effectiveness, superior mechanical attributes, and flexible processing characteristics. However, these polymers, sourced from fossil hydrocarbons, tend to accumulate in various environmental settings, including terrestrial and aquatic ecosystems, as well as coastal regions. Here, they may transform larger aggregates or degrade into micro- and nanoparticles, commonly referred to as microplastics. Additionally, these materials can settle in marine environments, where they persist and degrade over extended durations, presenting significant ecological challenges (Kupervaser et al. 2023; Wang et al. 2024). Thus, bioplastic and edible coatings/films represent innovative solutions in the quest for sustainable packaging materials, driven by increasing environmental concerns and the desire to reduce reliance on conventional plastics. Bioplastic encompasses a range of biodegradable materials derived from renewable resources, such as plant-based polymers, which offer the potential to mitigate the environmental impact associated with traditional packaging materials (Nanda et al. 2022; Nayak et al. 2024).
These materials are designed to degrade naturally, reducing pollution and waste accumulation in landfills and oceans. Edible coatings and films, on the other hand, are thin layers applied directly to food surfaces to extend shelf life, enhance quality, and provide additional functionalities, such as antimicrobial properties or flavor encapsulation (Fig. 9). Conversely, edible coatings are directly applied to the food surface via dipping or spraying techniques, followed by drying, thereby serving as a protective barrier. These applications often utilize natural macromolecules with film-forming capabilities, such as proteins and polysaccharides, to form a continuous matrix. Moreover, these substances act as carriers for a variety of functional additives and ingredients, including antimicrobials, antioxidants, colorants, nutraceuticals, minerals, vitamins, pigments, and flavorings (Kouhi et al. 2020; Pająk et al. 2019; Tafa et al. 2023). Despite the promise of bio-packaging and edible coatings/films, several challenges and considerations must be addressed to realize their full potential. Firstly, the performance of these materials, including mechanical strength, barrier properties, and stability, must meet the rigorous demands of packaging applications while maintaining biodegradability and safety for food contact. Additionally, issues such as cost-effectiveness, scalability of production, and regulatory compliance pose significant hurdles to widespread adoption. Balancing these factors requires multidisciplinary approaches, integrating expertise from materials science, food technology, engineering, and environmental science (Anugrahwidya et al. 2021; Rashwan et al. 2023a; Tafa et al. 2023).
Application of edible films or coatings to a food matrix, highlighting their role in incorporating and protecting various functional components. Antioxidants and probiotics are depicted as being delivered through these coatings, with specific inhibitors such as oxygen, ultraviolet light, microorganisms, carbon dioxide, and water labeled with their respective impacts on the food's preservation. Notably, edible coatings aim to block harmful elements like oxygen and ultraviolet light, which are known to degrade food quality, while simultaneously enhancing the food matrix with beneficial additives like flavor and aroma compounds. Overall, the illustration effectively communicates how edible films and coatings can serve as vehicles for functional ingredients while protecting food from environmental stressors, thus extending its shelf life, and enhancing nutritional value
For example, edible films were created using starches extracted from pumpkin fruits, lentil seeds, and quinoa seeds and were assessed alongside those made from potato starch to identify variations attributable to the botanical origin of the starch. The films from lentil starch displayed the lowest water solubility, highlighting their suitability for applications where water resistance is paramount, while pumpkin starch films demonstrated the highest swelling capacity, suitable for high moisture environments. These films exhibited tensile strengths ranging from 8.98 to 13.85 megapascals and elongation at break percentages from 3.35 to 4.44%, indicating that while they are relatively strong, they lack elasticity. Differential scanning calorimetry analyses confirmed that all films have good thermal stability, with endothermic peaks occurring between 249 and 281 °C, making them viable for various applications. However, they showed higher water vapor permeability compared to potato starch films, which may restrict their use in moisture-sensitive applications without additional modifications. Given their biodegradability and edibility, these starch-based films are promoted as eco-friendly alternatives for food packaging, offering potential enhancements in shelf life and food safety and presenting customizable properties for specific uses despite some limitations in elasticity compared to conventional potato starch films (Pająk et al. 2019).
Furthermore, pulsed light used in conjunction with antimicrobial starch films containing citric acid led to a reduction of Listeria innocua by an average of 4.5 log colony-forming units after three days of storage at 4 °C, demonstrating the efficacy of this combination in controlling surface contamination on cheese. However, significant alterations in the physicochemical properties of the cheese, such as pH, moisture level, and mechanical properties, were noted after seven days of refrigerated storage, suggesting that while microbial safety improved, the quality changes could potentially impact consumer acceptance. The antimicrobial starch films were formulated with additives such as sodium benzoate, citric acid, and a blend of both, which effectively acted as carriers for the antimicrobials, releasing them in a controlled manner to inhibit microbial growth (de Moraes et al. 2020). Despite the pulsed light treatment, the structural integrity of these antimicrobial starch films remained intact, indicating that the films preserved their functional properties under such exposure. The primary antimicrobial mechanism of the films is attributed to citric acid’s ability to lower pH, thereby creating an environment unsuitable for microbial proliferation, with antimicrobial starch films containing citric acid showing enhanced microbial reduction capabilities. Throughout the seven-day refrigerated storage period, cheese slices treated with antimicrobial starch films exhibited better microbial control than untreated slices. However, to balance safety with sensory attributes, the observed changes in pH and texture among treated cheese slices need further consideration to maintain overall product quality (de Moraes et al. 2020).
Another study investigated the effects of dialdehyde starch and silica solutions as additives on the properties of starch-based bioplastic films, formulating two types of bioplastics using either a 20% dialdehyde starch solution or a 20% silica solution, with additive concentrations varying from 60 to 100% based on the weight of cassava starch. Dialdehydes containing dialdehyde starch displayed a lower moisture content of 6.62–11.85% and water solubility of 4.23–7.90% compared to those with silica solution, which showed higher moisture content of 11.24–14.26% and water solubility of 7.77–19.27%, suggesting that dialdehyde starch enhances moisture resistance through chemical interactions that improve water resistance. Additionally, bioplastics with dialdehyde starch exhibited significantly higher tensile strength of 1.63–3.06 megapascals than those with silica solution of 0.53–0.75 megapascals, attributed to better miscibility and cross-linking between starch and dialdehyde starch (Oluwasina et al. 2021). Despite their advantages, bioplastics with dialdehyde starch were less biodegradable than those with silica, likely due to their lower moisture content and solubility, which restrict microorganisms and moisture penetration and subsequently degrade the material. The thermal stability analysis indicated that bioplastics with dialdehyde starch could withstand higher temperatures before degrading, which is advantageous for applications requiring exposure to higher temperatures. Atomic force microscopy analysis revealed smoother surfaces in bioplastics with dialdehyde starch compared to those with silica solution, correlating with their enhanced mechanical properties and lower solubility rates and indicating a better integration of the additive into the bioplastic matrix (Oluwasina et al. 2021).
Moreover, edible films were prepared using a blend of arrowroot powder, cornstarch, refined wheat flour, glycerol, pectin, and vinegar, with each ingredient selected for its contribution to film functionality, including mechanical strength, flexibility, and biodegradability. These films demonstrated mechanical properties with tensile strength ranging from 0.12 to 0.14 kg per square centimeter and elongation at break from 35 to 46%, enhanced by the addition of glycerol as a plasticizer to improve their flexibility and strength. Thermogravimetric analysis showed high thermal stability with significant degradation occurring between 200 and 300 °C, while they exhibited low water vapor permeability was 0.0019 to 0.0035 g·millimeter/square meter·day·millimeter of mercury, suggesting effective moisture barrier properties (Shanbhag et al. 2023). The films also displayed transparency values between 0.816 and 2.685, beneficial for protecting food from ultraviolet light, and biodegradability tests indicated significant decomposition after 22 days of soil burial, showcasing good environmental degradability. Scanning electron microscopy and Fourier transform infrared spectroscopy analyses revealed smooth surfaces and confirmed the absence of new chemical peaks, suggesting physical interactions such as hydrogen bonding among components rather than chemical transformations. The incorporation of pectin and vinegar particularly enhanced the mechanical and barrier properties, with vinegar also imparting antimicrobial properties that could extend the shelf life of packaged foods (Shanbhag et al. 2023).
Additionally, the development of ultraviolet-blocking edible films, utilizing a blend of corn starch and moringa gum with added pinecone extract, marks a significant advancement in sustainable food packaging. These films are designed to provide effective ultraviolet protection, extend shelf life, and maintain the quality of light-sensitive foods by incorporating natural ingredients, enhancing both the functionality and environmental friendliness of the packaging. The films contain varying concentrations of pinecone extract, including 3%, 5%, and 10%, which significantly boost their ultraviolet-blocking capabilities but influence their mechanical properties by reducing tensile strength and increasing flexibility, as evidenced by the elongation at break increasing from 3.27% in the control to 35.2% in films with 10% pinecone extract (Nayak et al. 2024). Additionally, the films demonstrated excellent ultraviolet protection, crucial for shielding food products from photochemical damage, attributed to the polyphenolic compounds in pinecone extract, such as quercetin, rutin, and kaempferol. Thermogravimetric analysis revealed that the films are thermally stable, undergoing typical decomposition stages for bio-based materials, with increased stability observed in films containing pinecone extract. However, these films exhibited moderate water vapor permeability, which increased with higher pinecone extract concentrations due to its hydrophilic nature and varied in color and transparency based on the pinecone extract concentration, with higher levels resulting in darker, more ultraviolet-opaque films. Given their biodegradable and edible qualities, coupled with their ultraviolet-blocking properties, these films offer a promising solution for the sustainable packaging of products sensitive to light (Nayak et al. 2024).
In conclusion, the pursuit of sustainable packaging solutions is underscored by the development of bioplastics and edible coatings that aim to reduce the ecological footprint of traditional petroleum-derived materials. These innovative materials, derived from natural sources like starches and incorporating additives such as citric acid or pinecone extract, not only fulfill the functional requirements of traditional packaging by enhancing food safety and extending shelf life but also offer improved biodegradability and reduced environmental impact. Challenges such as optimizing mechanical strength, barrier properties, and cost efficiency continue to drive research in this field, necessitating a multidisciplinary approach to develop viable and environmentally friendly alternatives to conventional plastics.
Starch in the textile industry
The textile sector ranks as the world's second most polluting industry, following petroleum, where wet textile processing is particularly detrimental to the environment, highlighting the crucial need for the adoption of sustainable chemicals in activities such as sizing, printing, and finishing textiles as a pivotal step toward fostering a sustainable textile industry. Starch plays a significant role in the textile industry, primarily as a sizing agent, where starch can be used to add stiffness and smoothness to yarns, facilitating weaving by reducing breakage and improving the fabric's appearance (Adewale et al. 2022; Meshram et al. 2009). Additionally, starch can be applied as a finishing agent to enhance the fabric's crispness and handle. The natural, renewable, and biodegradable properties of the starch make it an attractive choice for eco-conscious textile manufacturers. In the textile industry, sizing involves applying a protective adhesive layer to yarn surfaces to prevent breakage during weaving, enhancing yarn strength and resistance to abrasion against machinery (Fig. 10). Adhesion is vital for strengthening yarn by binding fibers together, reducing loose fibers, and improving bonding between the yarn and starch coating. However, native starch's brittleness hampers adhesion, prompting research into starch modification techniques such as cationization to address this issue (Li et al. 2018; Shen et al. 2021).
Preparation procedure of hydrolyzed and grafted starch, sizing, and weaving process. Starch is first subjected to hydrolysis, a process where the starch molecules are broken down into smaller fragments or hydrolyzed starch. This can be achieved through enzymatic or chemical hydrolysis methods, where enzymes or acids are used to cleave the starch molecules into shorter chains or individual glucose units. After hydrolysis, the hydrolyzed starch is then grafted with polymer chains or monomers to enhance its properties for sizing. This grafting process involves attaching polymer chains onto the hydrolyzed starch backbone, typically through chemical reactions such as free radical polymerization. The purified hydrolyzed and grafted starch is formulated into a sizing solution or paste. This sizing solution is applied to the yarns before weaving to provide them with the necessary stiffness, smoothness, and strength to withstand the stresses of the weaving process. The sizing solution can contain additional additives such as lubricants, antistatic agents, or preservatives to improve its performance and stability. After the yarns are sized, they are ready for the weaving process. During weaving, the sized yarns are interlaced to form the fabric structure. The sizing on the yarns helps reduce breakage and abrasion during weaving, leading to improved weaving efficiency and fabric quality
For instance, cationized starch, derived from pre-oxidized starch and treated with glycidyl trimethylammonium chloride, presents significant potential for textile sizing and printing, offering enhanced adhesion, viscosity, and printing efficacy. This modification process enables tailored adjustments to starch attributes, catering to specific needs within the textile sector, thus fostering more sustainable and efficient sizing and printing practices (Hebeish et al. 2005). Cationization of pre-oxidized starch resulted in varied degrees of substitution, ranging from 0.013 to 0.065, influencing adhesion and viscosity, crucial for ensuring consistent sizing and printing quality in textile applications. Enhanced adhesion strength, reaching up to 8.6 Newtons per square centimeter with higher degrees of substitution values, is attributed to increased positively charged amino groups on starch molecules, fostering stronger interactions with fabric surfaces. The cationized starch demonstrates excellent printing performance, yielding clear, durable patterns with good color and wash fastness, while reduced surface tension enhances fabric wetting and penetration during processing. Despite treatment, fabrics maintain mechanical integrity post-printing, indicating negligible alteration to tensile properties (Hebeish et al. 2005).
Furthermore, the graft copolymers of starch exhibit considerable promise as textile sizing agents, enhancing cotton fabric's mechanical strength, water resistance, and dyeing characteristics. The adaptability of graft copolymerization enables the tailoring of starch-based polymers to precise textile needs, fostering sustainable and high-performance textile materials. Various monomers, including acrylamide, acrylonitrile, and methyl methacrylate, were graft copolymerized with starch, utilizing ceric ammonium nitrate as the initiator (Meshram et al. 2009). Successful monomer incorporation onto the starch backbone was indicated by grafting efficiencies ranging from 17.8 to 40.4%, confirmed by Fourier transform infrared spectroscopy. Besides, the thermal analysis highlighted alterations in thermal stability and degradation behavior compared to native starch. Applied as sizing agents, these graft copolymers significantly bolstered the tensile strength, elongation at break, and water resistance of cotton fabrics. Treated fabrics exhibited an enhanced tensile strength of 30.2 to 37.8 Newtons per square millimeter and reduced water absorption of 90–100% compared to untreated counterparts of 26.1 Newtons per square millimeter and 135% water absorption. The graft copolymers' negligible impact on dyeing properties, evidenced by comparable color strength and dye uptake, underscores their compatibility with textile processing, ensuring fabric coloration remains unaffected (Meshram et al. 2009).
Additionally, incorporating starch nanoparticles into textiles presents a promising strategy for creating robust materials with enhanced mechanical properties, water resistance, and thermal stability, crucial for applications in demanding industries like automotive, aerospace, and protective clothing. Produced through acid hydrolysis, the starch nanoparticles, averaging 80 nm in size and possessing a high surface area of 96.3 square meters per gram, function as reinforcing agents due to their substantial aspect ratio and surface area, facilitating effective interaction with textile fibers (Mostafa et al. 2019). Their integration into textiles yielded significant enhancements in mechanical properties, with a 52% increase in tensile strength of 32.7 megapascals and a 35% improvement in flexural rigidity of 32.8 mN compared to untreated textiles. Surface modification of the starch nanoparticles with a coupling agent bolstered their compatibility with textile fibers, promoting better adhesion and dispersion within the textile matrix, consequently reinforcing the material overall. Furthermore, the reinforced textiles exhibited notable improvements in water resistance, with a decrease in water absorption from 1.75 to 0.95%, indicating reduced moisture uptake and heightened durability in moist conditions. The thermogravimetric analysis confirmed enhanced thermal stability in the reinforced textiles, evidenced by a 20 °C increase in the onset temperature of degradation compared to untreated textiles, thereby augmenting resistance to heat-induced degradation (Mostafa et al. 2019).
Moreover, hydroxypropylation of corn starch proves effective in lowering gelatinization temperature, enhancing viscosity, and improving film-forming abilities, positioning it as a promising sizing agent for textiles. The resulting textiles showcase enhanced mechanical properties and wash fastness, underscoring hydroxypropylated starch's potential to elevate textile performance and durability. Corn starch undergoes hydroxypropylation to introduce hydroxypropyl groups onto starch molecules, resulting in varying degrees of substitution ranging from 0.013 to 0.051. Gelatinization temperature decreases with rising degrees of substitution, facilitating easier starch swelling and dispersion in water, which is crucial for textile sizing processes (Shen et al. 2021). Increasing degrees of substitution correlates with heightened viscosity of starch solutions ranging from 290 to 1850 millipascal seconds, pivotal for achieving consistent sizing and film formation on textile fibers. Hydroxypropylated starch yields films with smoother surfaces and better fiber adhesion, enhancing sizing effectiveness in bolstering textile mechanical properties. Textiles treated with hydroxypropylated starch exhibit improved tensile strength ranging from 23.5 to 27.8 Newton per square millimeter compared to untreated counterparts was 20.1 Newton per square millimeter, attributed to enhanced sizing efficiency and film quality. Furthermore, textiles sized with hydroxypropylated starch demonstrate robust wash fastness, preserving tensile strength even after multiple washing cycles, and validating the longevity of starch sizing in textile applications (Shen et al. 2021).
In summary, the textile industry ranked as the world's second most polluting sector after petroleum, necessitates the adoption of sustainable chemicals in activities like sizing, printing, and finishing to mitigate environmental impact. Starch serves a crucial role in textile processing, offering stiffness and smoothness to yarns and enhancing fabric properties as a sizing and finishing agent. Modification techniques like cationization improve starch's adhesion properties, enhancing its efficacy in textile applications. Additionally, graft copolymers and starch nanoparticles show promise in enhancing textile mechanical properties, water resistance, and thermal stability, catering to diverse industry needs. Hydroxypropylated corn starch emerges as a viable sizing agent, lowering gelatinization temperature and improving film-forming capabilities, thereby enhancing textile performance and durability.
Wood adhesives
Starch-based wood adhesives have emerged as a sustainable and eco-friendly alternative to conventional synthetic adhesives in the woodworking industry. Derived from renewable plant sources, starch offers several advantages, including biodegradability, non-toxicity, and abundance, making it an attractive choice for environmentally conscious applications. In recent years, there has been growing interest and research in developing starch-based adhesives for various wood bonding applications, ranging from furniture manufacturing to construction. Starch-based adhesives are typically prepared by modifying native starch through chemical or physical methods to improve its adhesive properties, such as bonding strength, water resistance, and setting time (Din et al. 2020; Wang et al. 2012; Xing et al. 2018; Zhang et al. 2015). Common modifications include enzymatic hydrolysis, acid, or alkaline treatment, and blending with other polymers or additives to enhance performance. One of the key advantages of starch-based wood adhesive is its compatibility with wood substrates, forming strong and durable bonds while minimizing environmental impact. Additionally, starch-based adhesives offer cost-effectiveness and ease of processing compared to synthetic alternatives, further enhancing their appeal to industries seeking sustainable solutions. However, challenges remain in optimizing the properties of starch-based adhesives to meet specific application requirements, such as high-humidity environments or outdoor exposure. Research efforts are focused on addressing these challenges through innovative formulation techniques, including nanoparticle reinforcement, cross-linking agents, and novel processing methods (Gu et al. 2019; Nasiri et al. 2020; Wang et al. 2011; Wu et al. 2020).
For instance, the addition of 10% silica nanoparticles to starch-based wood adhesive significantly enhanced its bonding strength, increasing by 50.1% in dry conditions and 84.0% in wet conditions, likely due to strengthened molecular interactions, as evidenced by Fourier transform infrared spectroscopy analysis which confirmed successful graft polymerization. Furthermore, the water resistance of the adhesive improved by 20.2%, attributed to the nanoparticles maintaining the adhesive's structural integrity in moist environments (Wang et al. 2011). Scanning electron microscopy analysis revealed a more compact and smoother matrix in the adhesive, contributing to a cohesive fracture pattern observed within the adhesive layer during shear tests, indicating a robust internal structure. Additionally, thermogravimetric analysis showed an increase in initial decomposition temperatures, suggesting enhanced thermal stability due to the nanoparticles. The adhesive also exhibited more pseudoplastic behavior with increased silica content, evidenced by a lower flow behavior index and higher consistency index, enhancing its viscosity, and improving application properties on wood surfaces. The interaction of nanoparticles with the hydroxyl groups of grafted starch enhances hydrogen bonding and Van der Waals forces, leading to observed improvements in mechanical and thermal properties, as well as water resistance. Overall, the incorporation of silica nanoparticles significantly improves the performance and application qualities of starch-based wood adhesives (Wang et al. 2011).
Furthermore, the adhesive was synthesized via graft polymerization, using vinyl acetate monomer grafted onto gelatinized waxy corn starch with ammonium persulfate as the initiator, resulting in a grafted starch adhesive that significantly outperformed a commercial blend of polyvinyl acetate and gelatinized starch. Specifically, the shear strength of the grafted adhesive in dry and wet states increased by 59.4% and 321%, respectively, with a corresponding 61.1% improvement in water resistance. The study found that a starch/monomer ratio of 1:1.2 weight per weight was most effective, achieving optimal bonding characteristics with shear strengths of 4.30 megapascal in dry conditions and 2.17 megapascal in wet conditions (Wang et al. 2012). Besides, Fourier transform infrared and 1H nuclear magnetic resonance spectroscopy confirmed the successful grafting of vinyl acetate onto the starch, while thermogravimetric analysis indicated enhanced thermal stability, reflecting a strengthened molecular structure. Scanning electron microscopy revealed that the grafted starch-based adhesive formed smoother and more compact films compared to the polyvinyl acetate/starch blend, indicating better compatibility and reduced phase separation. Scanning electron microscopy analysis of the fracture surfaces on glued wood specimens showed more effective penetration by the grafted adhesive, leading to improved bonding characteristics. These enhancements not only improve the mechanical properties and water resistance of the starch-based adhesive but also its interaction with wood, positioning it as a viable, environmentally friendlier alternative to traditional petroleum-based adhesives (Wang et al. 2012).
The authors developed a new bio-adhesive by integrating cassava starch with bio-oil derived from the fast pyrolysis of larch sawdust, resulting in improved liquidity, an extended shelf life from 13 to 55 days, and enhanced shear strength. This bio-adhesive demonstrated a 17.4% increase in bonding strength in dry conditions and a 50.9% increase in wet conditions with the addition of 25% bio-oil, while its water resistance improved by 10.0%. The bio-oil's composition, including 34% phenolic compounds, 30% water, 15% organic acids, and 21% other compounds such as sugars, esters, ketones, and aldehydes, played a crucial role in enhancing the adhesive's properties through chemical functionality. Notably, the phenolic hydroxyl groups, along with carboxyl and aldehyde groups in bio-oil, reacted with the hydroxyl groups of starch, enhancing the adhesive's molecular structure and optimizing stability. Fourier transform infrared spectroscopy and scanning electron microscopy analyses showed that the bio-oil–starch adhesive had a more cross-linked and compact molecular structure compared to traditional starch-based adhesives, evident from sharper absorption peaks and tighter linkage between starch molecules. Thermogravimetric analysis indicated that the bio-oil–starch adhesive had improved thermal stability and altered thermal degradation profiles, suggesting enhanced thermal resistance (Xing et al. 2018).
Moreover, the development of a separable paper adhesive from a starch–lignin composite aims to enhance the recyclability of paper products, achieving optimal adhesion under specific conditions: a mass ratio of water to starch at 15:1, sodium lignosulphonate to starch at 0.15:1, ammonium persulfate to starch at 0.02:1, a pH of 4, and a reaction temperature of 80 °C for 6 h. Lignin, known for its multiple reactive groups and benzene rings, was utilized to bolster the shear strength and thermal stability of the adhesive. Ultraviolet–visible spectrophotometry confirmed the presence of lignin, showing absorption peaks characteristic of lignin’s phenolic structures (Wu et al. 2020). The grafting copolymerization of lignin onto the starch backbone enhanced the adhesive's mechanical and bonding properties while preserving the starch's biodegradability. Analytical techniques, including Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction, verified the successful integration of lignin, improving the adhesive's stability and adhesion. The modified starch exhibited an increased thermal decomposition temperature, indicating a boost in thermal stability due to lignin incorporation. Moreover, the adhesive's design allows for easy separation during paper recycling by simple dissolution in warm water, addressing a major challenge in paper recycling where traditional adhesives complicate the reprocessing of paper fibers (Wu et al. 2020).
Furthermore, the study by Chen et al. (2021b) provides a comprehensive comparison of the physicochemical properties and adhesive performance between corn starch and cassava starch, revealing that corn starch has an amylose-to-amylopectin ratio of 23:77, while cassava starch features a ratio of 17:83. Scanning electron microscopy images depict that corn starch granules are irregular and sharp-edged, in contrast to the more uniform, regular, and rounded granules of cassava starch. Differential scanning calorimetry analyses indicate that cassava starch has a lower gelatinization temperature than corn starch, suggesting higher stability and finer gel formation in cassava starch. X-ray photoelectron spectroscopy results show a higher oxygen content and slightly lower carbon content in cassava starch. When tested for bonding strength on plywood, the adhesive made from cassava starch demonstrated a higher initial viscosity of 450 millipascal seconds and greater dry shear strength than the corn starch adhesive, which had an initial viscosity of 194 millipascal seconds. The addition of polymeric methylene diphenyl diisocyanate (PAPI) pre-polymer to both starch adhesives enhanced their wet shear strength, showcasing the potential of chemical modifications to improve the water resistance of starch-based adhesives. Overall, the study suggests that the superior performance of cassava starch adhesive on plywood is linked to its physicochemical properties despite the challenges posed by its higher initial viscosity (Chen et al. 2021b).
To summarize, starch-based wood adhesives, developed from renewable sources such as cassava and corn starch, are proving to be sustainable alternatives to traditional synthetic adhesives, offering significant environmental benefits, including biodegradability and non-toxicity. Innovations such as the incorporation of silica nanoparticles and graft polymerization techniques have not only enhanced the mechanical properties and water resistance of these adhesives but also improved their bonding strength and thermal stability, making them viable for demanding applications like furniture manufacturing and construction. However, despite these advancements, challenges persist in achieving optimal performance under conditions of high humidity or outdoor exposure, necessitating ongoing research into novel formulations and processing methods to realize the full potential of starch-based adhesives in the woodworking industry.
Conclusion
Environmentally friendly extraction and modification techniques for plant-based starch are critical areas of innovation, driven by the escalating demand for starch in diverse industries and the need for sustainable practices. Starches such as maize, rice, potatoes, and cassava are integral to global food systems and various industrial applications. With annual production estimates exceeding 90 million metric tons, the starch industry plays a significant role in both the global economy and resource utilization. Traditional starch processing methods are noted for their environmental drawbacks, including high energy consumption and substantial chemical waste, which collectively account for around 60% of total energy expenditure in starch manufacturing. In contrast, alternative starch modification techniques are increasingly recognized for their potential to reduce these environmental impacts. Enzymatic and physical modification methods are emerging as favorable alternatives, demonstrating a reduction in energy usage by up to 50% compared to conventional methods. Enzymatic treatments, which allow for precise modifications to the starch structure without extensive collateral damage, have been shown to decrease the use of harsh chemicals by over 30%. These methods improve the solubility and thermal properties of starch, enhancing its applicability in various products.
Physical modification techniques, including heat–moisture treatment, annealing, and ultrasonication, are also gaining traction. These techniques not only enhance the functionality of starch in food applications by improving water retention and resistance to retrogradation but also increase the digestibility of starch by 20%. Such benefits make these methods particularly appealing to the food processing industry. The application of modified starches extends beyond food. In the production of bioplastics, the use of modified starch has led to a reduction in non-renewable resource use by 40%. In the pharmaceutical sector, modified starch has increased the efficiency of drug delivery systems by 25%, demonstrating the versatile potential of these innovations. Despite these advances, challenges remain, particularly in scaling up these technologies and fully understanding their environmental impacts. Further research into the life cycle assessments of these technologies is essential to quantify their true environmental benefits. Additionally, there is a push for more investment in biotechnological advancements, such as genetic modification and nanotechnology, which could lead to even more significant improvements in starch production efficiency and sustainability. Overall, the shift toward environmentally friendly starch extraction and modification methods offers promising avenues for reducing the ecological footprint of this essential industry while maintaining its economic viability. The ongoing development and application of these technologies are crucial for promoting sustainability in starch production and utilization.
Data availability
The references for the data used have been cited.
Code availability
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Acknowledgements
Dr. Ahmed K. Rashwan would like to thank Zhejiang University and Zhejiang Province for providing a postdoctoral Fellowship position for him and supporting his research. Dr. Ahmed I. Osman wishes to acknowledge the support of The Bryden Centre project (Project ID VA5048), which was awarded by The European Union’s INTERREG VA Program, managed by the Special EU Programs Body (SEUPB), with match funding provided by the Department for the Economy in Northern Ireland and the Department of Business, Enterprise, and Innovation in the Republic of Ireland.
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This work was supported by the National Key R&D Program of China (2022YFF11002), and Open Project of Wencheng Joint Research Center of Big Health Industry of Zhejiang University (Zdwc2205).
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Ahmed K. Rashwan was responsible for conceptualization, methodology, software, writing—original draft, and writing—reviewing and editing. Hala A. Younis was involved in methodology, writing—original draft, and writing—reviewing and editing. Asem M. Abdelshafy and Mohamed R. Eletmany contributed to writing—original draft and writing—reviewing and editing. Ahmed I. Osman assisted with resources, conceptualization, and writing—editing. Mahmoud A. Hafouda took part in writing—original draft. Wei Chen assisted with conceptualization, supervision, resources, and writing—reviewing and editing.
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Rashwan, A.K., Younis, H.A., Abdelshafy, A.M. et al. Plant starch extraction, modification, and green applications: a review. Environ Chem Lett (2024). https://doi.org/10.1007/s10311-024-01753-z
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DOI: https://doi.org/10.1007/s10311-024-01753-z