Introduction

Despite growing at a slower pace, world population is expected to reach 9.7 billion in 2050 and could peak at nearly 11 billion around 2100 [1]. To accommodate this number, current food production will need to nearly double. This is a significant challenge for society, which it must accomplish while trying to follow most of the sustainable development goals [2]. The partial replacement of meat protein by vegetable protein may be a possible means of reducing the carbon footprint. Moreover, consumers are becoming increasingly aware of their fat intake and concerned about the products they include in their diets, because lifestyle habits and a diet rich in saturated fats, cholesterol, and salt have been shown to be risk factors for cardiovascular disease [3]. Bearing all these factors in mind, it is necessary to look for more sustainable and healthier products, which contribute to enhancing welfare and achieving ecological balance.

Moringa oleifera is a rapidly developing tropical crop, little known in developed countries but widely cultivated in Africa, Central and South America, Sri Lanka, India, Mexico, Malaysia, Indonesia and the Philippines since ancient times [4]. This crop has great industrial potential and is also well adapted to climate change because it needs little water and has few agricultural requirements, as was recently reported by the authors [5]. In addition, each one of its parts has significant nutritional properties, in particular their content in proteins, fiber, antioxidants [6, 7] and minerals. Thus, the leaves are used as nutritional supplements, the seeds for water purification, the oil as a biofuel, the trunk as a gum producer, the flowers as a source of honey, and every part of the plant can also be used for therapeutic purposes [8]. Remarkably, the oil produced from the seeds has a similar level of C18:1 to olive oil [9]. Moreover, in the developing countries, sources of vitamin A, such as drumstick leaves, are invaluable in the struggle to overcome the problem of vitamin A deficiency [10]. Hence, M. oleifera trees are being promoted as a dual solution to mitigate the impacts of climate change, while also providing an alternative source of income for families since these trees are easy to plant and do not require much maintenance [5].

The food industry might offer traditional products fortified with sustainable sources, such as the different parts of moringa, promoting the consumption of this plant. However, there is a lack of knowledge as regards the potential uses of moringa in the area of food fortification [11]. To that end, the objective of this paper is to collect recent information obtained from scientific references where moringa has been incorporated into a variety of food matrices (bread, bakery products, snacks, beverages, dairy and meat products) in order to discover its effect on technological properties and sensory acceptance.

Application in Different Food Matrices

Bread, Bakery Products and Snacks

Despite its low nutrient content, bread is a staple food the world over due to its high-energy input. Micronutrient deficiency is increasing among children and pregnant women in Africa and other developing countries [12]. In order to know how different parts of moringa contribute to the nutritional enrichment of bread, an extensive search for the information published in scientific articles over the last 10 years has been conducted and the results collected in Table 1. Specifically, seed flour and dry moringa leaf powder are mainly used to fortify bread dough prepared from either wheat flour or in combination with other flours. Moreover, this replacement can be a good alternative means of elaborating gluten-free bread intended for coeliacs, it being a good way to provide appropriate levels of minerals, proteins, phenols and other nutrients. The concentrations used to fortify bread with dry leaf powder and seed flour range from 1–15 to 1–5%, respectively. It is worth noting the viability and potentiality of the use of seed flour because it is just as rich in protein as the leaf [13]. Most of the authors highlight the improvement in the protein and fiber content of moringa-rich bread; in some cases, a decrease in moisture is also reported together with the subsequent shelf-life extension [14, 15]. However, negative characteristics are also registered, mainly related with mechanical properties (lower height, less volume and sponginess than the control) [14, 16,17,18]: this is probably due to gluten deficiency as a result of adding a greater proportion of moringa in the bread dough, as stated by some authors [16, 17]. Other authors conclude that in addition to gluten deficiency, the antimicrobial properties of moringa leaves have a significant impact on yeasts; this affects the structure of bread, as it is less rich in alveoli [14]. Also, concentrations of over 5% of seed flour and approximately 10% of dry leaf powder lead to low sensorial acceptance due to the dark green color, the herbal taste and the increased hardness of the bread.

Table 1 Moringa fortified breads
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Moringa may also be incorporated into other bakery products which, in spite of being less significant as regards people’s diets than bread, are widely consumed by all age ranges in different societies. In the last few years, moreover, industry has mass produced them with processed egg products, using “trans” fats and a high sugar content; the objective was to offer the products at low prices, which has led to an increase in the consumption of these kinds of industrial pastries that, in turn, has resulted in chronic diseases, such as obesity and cardiovascular diseases [22]. Industry is conscious of the need to improve the nutritional profile of these products and is making a great effort to develop healthier bakery foods, using natural products useful for disease prevention. In this regard, Table 2 has compiled data obtained from scientific articles over the last eight years dealing with the fortification and, therefore, nutritional improvement of biscuits, cakes, brownies and muffins that use different parts of moringa. As can be seen, dry leaf powder (1–20%), seed powder (10–30%) and, to a lesser extent, leaf extract (15–30 mL) replaced part of the wheat flour in cookies, muffins, brownies, etc. The beneficial properties of the fortification of these kinds of products are related with an increase in the nutritional content, above all in protein and fiber, and also with a greater antioxidant activity. In the case of vegetarians, for example, moringa leaves may be an alternative to milk and eggs in cookies that would enable them to consume the same content of proteins [23, 24]. It is noticeable that high concentrations of seed powder, around 20%, resulted in a good sensory acceptance as a result of the characteristic flavor imparted by the seed, which is very similar to the taste of the nut [21, 25]. However, the reformulation of bakery products also has some drawbacks, especially when 7–20% moringa is incorporated into these matrices; as a consequence, they exhibit greater compaction, unwanted odors and herbal flavors and a greenish coloration, all of which implies consumer rejection. These technological shortcomings can be overcome by coating the product with a chocolate layer, as reflected by these authors [23, 24], adjusting the amount or selecting the appropriate baking powder, among other strategies.

Table 2 Moringa-fortified bakery products
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Other cereal-based products, such as the snacks (bars, squares and tortilla chips…), are appreciated by consumers for their taste. However, their nutritional profile is often very poor, since they have high amounts of sugars and fats, and are scarce in proteins and other nutritional compounds, such as antioxidants. In this regard, these food matrices have been submitted to different fortifications in terms of fiber, vitamins or proteins [32,33,34,35,36]. Table 3 collects the scientific studies published over the last few years in which moringa seed flour, and especially dry leaf powder, have been added to different snacks in widely differing quantities: 0.6–45% and 2.5–7.5%, respectively. As in bread and bakery products, there is a reported increase in the content of proteins, minerals, essential amino acids and fiber. In most cases, these snacks are aimed at specific sectors of the population, ones in which nutrient requirements are greater (athletes, elderly people, children with malnutrition, etc.) [32, 37]. Again, mechanical (hardness and swelling capacity) and sensorial properties (dark green color and astringent flavor) conditioned their acceptance [33, 35].

Table 3 Snacks fortified with moringa
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Beverages

These food matrices are easily consumed along with meals and so they are good vehicles for the delivery of nutritional supplements into the body [40]. Beverages are by far the most active category of functional foods due to: (i) their convenience and the possibility of meeting consumer demands as regards container contents, size, shape, and appearance; (ii) their ease of distribution and the fact that they are a better means of storage for refrigerated and shelf-stable products; and (iii) the fact that they represent a great opportunity to incorporate desirable nutrients and bioactive compounds since homogeneous blending is easily achieved [41, 42]. In this section, beverages made of raw materials of vegetable origin, such as tubercles, grains, seeds, fruits and herb leaves are considered. Protein is one of the most deficient components in this type of product and, therefore, the addition of different parts of moringa would improve their nutritional profile [43], giving rise to products rich in all-vegetable protein. Thus, Table 4 shows the studies carried out with this aim in mind, which might help to broaden the range of products for those who may either have some type of intolerances or follow a type of vegetarian diet. As can be seen, dry leaf powder, fresh leaf, leaf infusion and leaf aqueous extract were the most commonly used parts of moringa, in percentage ranges of 1.1–100%, 1.5–4.5%, 50%, 10–50%, respectively. An increase in the nutritional value, especially of the antioxidant capacity and the content of phenols and proteins, was the main beneficial aspect described. As for the problematic characteristics, the higher concentrations imparted a bitter taste due to the presence of catechin (phenolic compound that the moringa leaf possesses) and caused an undesirable greenish coloration, flavor degradations over time and a loss of quality if stored more than a week due to the ease with which moisture is absorbed. Some of the authors pointed out the need for more research into the incorporation of aqueous leaf extract into beverages [44] and the difficulty for some consumers to accept certain drinks due to the characteristic taste and color [43, 45].

Table 4 Drink fortified with moringa
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Dairy Products

Milk and its derivative products are generally not regarded as a rich source of particular bioactive ingredients, such as polyphenols and antioxidants, in spite of their many healthy and nutritious characteristics. Thus, health-conscious consumers are demanding more and more novel dairy products formulated using medicinal herbs or their extracts [48]. In this regard, Table 5 shows a compilation of recent publications in which dairy products have been reformulated using different parts of moringa. These studies focus on yogurt, curd and cheese. In the case of yogurt, [49,50,51] a concentration of 0.5–2% of dried moringa leaves was employed, whereas in the study carried out by Zhang et al. [52], the yogurt was supplemented with 0–0.2% moringa extract (ME; hot water extract, 100 °C, 30 min). Dhawi et al. [48] added 0.1 and 0.2% of Moringa oleifera seed flour to yogurt. Most of the beneficial features reported in these papers are linked to the maintenance of the sensory acceptance, the higher content of some amino acids (alanine acid, glutamine and tyrosine) and the enhanced antioxidant activity. Furthermore, moringa exerts control against pathogenic bacteria, such as E. coli, S. aureus, L. monocytogenes and Salmonella spp, without negatively affecting L. rhamnosus or L. acidophilus growth, also increasing the content in Ca, P, K, and Fe. However, a decrease in L. rhamnosus, lower viscosity and whiteness and less cysteine, methionine and histidine were found after five weeks of storage at 4 ºC. In most cases, a light green color was also registered. Moringa pod powder was incorporated into curd, consequently showing higher levels of vitamins A and C, iron, fiber and potassium than the control sample [53]. Labneh cheese [54], soft white cheese [51] and cream cheese [55] were prepared with 1–3% of dry moringa leaves or an ethanolic extract of dry leaves. As in previous cases, the nutritional value increased with acceptable organoleptic scores, although they had a lower degree of whiteness than the control.

Table 5 Dairy products fortified with moringa
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Meat Products and Their Plant-Based Analogues

Of the current consumer trends, one is the growing market for vegetarian and vegan foods; in recent years, this growth has been powered either by moral principles or because it is beneficial for both people’s health and the environment. In the human diet, protein intake is essential and, although there is a tendency to replace it with sources of plant origin, this comes mostly from animals [56]. In general, society consumes a large quantity of animal products, especially the young; in many cases, the production of these products (hamburgers, sausages, nuggets…) is based on low-cost meat with a high fat content. In addition, the impact of livestock on the environment is reflected directly and indirectly in the water, soil and air (generating greenhouse gases that increase the global temperature of the planet). Despite the high protein content of moringa, there are no scientific studies into the total substitution of protein in products traditionally made with protein of animal origin.

As regards the production of meat products, there is also a growing demand for natural effective antioxidants, because they are increasingly considered safer for consumption. Synthetic antioxidants, widely used in the food industry to lengthen the shelf life and improve the color and taste stability of meat products, have been considered in some studies to be a risk factor for degenerative diseases, such as cancer [57, 58]. As an alternative, the food industry is looking for natural sources of antioxidants, such as moringa. In this sense, Table 6 shows some studies that focus on analyzing the effect of the addition of moringa on various properties of meat products. As can be seen, the incorporation of moringa (aqueous extract of dried or fresh leaf, dried leaves, leaf powder, flower extract and seed flour) into meat products, such as sausages, chorizo, nuggets, minced meat and mortadella with raw material (beef, chicken, buffalo, pork and goat), is performed with the twofold purpose of inhibiting lipid oxidation [3, 59,60,61,62] and obtaining antioxidant and antimicrobial effects during storage, as recorded by these authors [63, 64]. Most of the authors agree that the great disadvantage is that high concentrations give rise to unwanted flavors and colorations and textural changes in the final product.

Table 6 Meat products and their plant-based analogues fortified with moringa
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Some authors, in particular Madane et al. [61] and Verma et al. [62] recorded that the incorporation of flower extract increases the content of dietary fiber, ashes and phenolics and also improves the cooking yield of the final product. However, high concentrations of flower extracts (2%) led to an increase in the lightness and a reduction in the hardness, redness and chewability of nuggets.

Conclusions

In this article, recently published scientific studies have been presented corroborating the potential of Moringa oleifera as an ingredient in different food matrices. It has been incorporated in most cases as dry leaf powder and seed flour to fortify breads, pastries (cookies, cakes, brownies, muffins) and cereal-based snacks. In those cases, all of the authors reported an improvement in the content of the proteins, essential amino acids, minerals and fiber of the final product. In some cases, an improvement in antioxidant capacity and a decrease in humidity have also been registered, thus extending the shelf life. In general, the negative consequences brought about by the antimicrobial properties of moringa that affect the action of yeasts are related to both the mechanical properties (lower height, less volume and fluffiness than control) and also to the sensory properties (dark green color and astringent flavor) that conditioned its acceptance.

Vegetable drinks are also food matrices fortified with moringa dried leaf powder, fresh leaf, leaf infusion or aqueous leaf extract, exhibiting an increase in nutritional value in every case, especially in terms of antioxidant capacity, and phenolic and protein content. However, higher concentrations imparted a bitter taste due to the presence of catechin, which produced an undesirable greenish coloration.

Dairy products, such as yogurt, curd and cheese, have also been fortified using different parts of moringa, giving rise to good sensory acceptance, a higher content in some amino acids (alanine acid, glutamine and tyrosine) and an improvement in antioxidant activity.

Finally, moringa was incorporated into meat matrices in very small proportions, the main objective of which was to search for its antioxidant and antimicrobial properties. In general, most authors agree that very small additions (1–2%) have an impact on changes in color, texture and flavor, as detected by tasters.