Chickpea aquafaba: a systematic review of the different processes for obtaining and their nutritional and technological characteristics

Aquafaba is the residual water from cooking chickpea in water. It has a high gelling ability, allowing it to create stable gels. However, those functional properties depend on the legume composition, genotype, cooking time, pressure, and temperature. This study aimed to evaluate the different processes for obtaining aquafaba and compare their nutritional composition and technological characteristics using a systematic review. The authors performed the systematic review by performing specific search strategies for Scopus, Web of Science, Pubmed, Lilacs, Google Scholar, and ProQuest. A total of 17 studies were analyzed. Of them, 17.64% (n = 3) used the wastewater from canned chickpeas, 17.64% (n = 3) compared the wastewater of canned chickpeas and dry grains, and 58.82% (n = 10) used dry chickpeas. Studies used different methods to analyze the protein content. The most used (n = 5) was the Association of Official Analytical Chemists (AOAC). The aquafaba presented carbohydrates at 2.03–2.59 g/100ml; protein at 0.0.8–2.8 g/100ml; and fat at 0.07–0.1 g/100ml. In general, preparing aquafaba followed: soaking (8–10 h at 4 °C—1 chickpea: 4 water), pressure cooking (30 min—2 chickpea: 3 water), and refrigerating (24h/4 °C). In general, the results showed the following steps to prepare aquafaba: soaking for 8–10 h at 4 °C at the proportion of 1:4 (chickpea:water), pressure cooking for 30 min in the proportion of 2:3 (chickpea: water), and refrigerating 24 h/4 °C. These procedures in a homemade aquafaba presented the best results, considering foam development and higher stability. The aquafaba from canned chickpeas has a higher foam-ability and lower emulsion properties than homemade cooking aquafaba. Supplementary Information The online version contains supplementary material available at 10.1007/s13197-023-05920-y.


Introduction
Plant-based food products as substitutes for animal sources have been considered healthy and eco-friendly in the past few years.This market growth is mainly from populations with specific dietary choices, such as vegans and vegetarians (He et al. 2019).The demand for alternative egg products has increased, especially for those that do not compromise the sensory, mainly taste and texture, and technological properties such as foaming, emulsifying, and heat coagulation that the eggs contribute to the food (Buhl et al. 2019a;Meurer 2019).Plant-based products replicating eggs' qualities are becoming increasingly popular among vegetarian individuals and people allergic to animal food.Among food allergies, eggs (mainly egg whites) are one of the most common, particularly among children, with prevalences ranging from 0.5 to 2% (Caubet and Wang 2011; Mustafa et al. 2018;Shim et al. 2018).For those reasons, the search for products using egg substitutes increases without giving up the taste and functional properties that eggs bring to food (Buhl et al. 2019a).
Aquafaba, the residual byproduct solution (about 90-95% water) from canning, boiling seeds, or other pulses in water, may improve the sensory and technological quality of eggfree food products due to its emulsion, foamability, stability, moisture retention, adhesion, gelation, and thickening properties.The most common one is produced using chickpeas.Chickpeas are grown mainly in South Asia, accounting for around three-fourths of the world's area (planted on a surface of 11 million ha).Its sales in the global market are projected to increase from US$ 12 million to U$ 21 million in 2032, highlighting the importance of aquafaba in the world (Future Market Insights 2022).However, only recently was aquafaba understood as an ingredient with technological importance, once interpreted as a waste of no industrial importance whatsoever (Mustafa and Reaney 2020).In this manner, multiple studies report the use of chickpea aquafaba as an enhancer or substitute to mostly egg whites, providing a viable usage and adding monetary value to an ingredient previously wasted (Mustafa et al. 2018;Anwar et al. 2019;Buhl et al. 2019aBuhl et al. , 2019b;;Raikos et al. 2020;Nguyen et al. 2021).The properties of chickpea aquafaba are mainly due to its proteins, carbohydrates (starch, oligosaccharide, cellulose, hemicellulose, lignin), polysaccharide-protein complexes, saponins, and phenolic compounds (Alsalman et al. 2020a(Alsalman et al. , 2020b;;Alsalman and Ramaswamy 2021a;He et al. 2021).
Aquafaba's use in food products depends on its consistency, composition, and quality, and its production standardization is a difficult task necessary to ensure the products' quality.Several parameters to assure its composition and functionality should be considered in aquafaba production, such as the type of pulse, water/pulse ratio, temperature, cooking pressure, and cooking time.Some studies evaluated aquafaba production or composition (Shim et al. 2018;Buhl et al. 2019a;He 2019;He et al. 2019;Lafarga et al. 2019a;Meurer 2019;Nguyệt 2019;Alsalman 2020;Alsalman et al. 2020b;Alsalman andRamaswamy 2021a, 2021b;Aslan and Ertaş 2021;Editors et al. 2021;Landert et al. 2021;Nguyen et al. 2021).However, to our knowledge, there is no production standardization, and the nutritional and technological properties of aquafaba have not yet been well explored.The hypothesis is that there is the best way to produce chickpea aquafaba, considering nutritional and technological characteristics.Therefore, this study aimed to evaluate the different processes for obtaining chickpea aquafaba and compare their nutritional quality and technological characteristics through a systematic review.

Methods
This systematic review was performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and its Checklist (Moher et al. 2009;Page et al. 2021).Also, registers of the ongoing systematic reviews were searched via PROSPERO (Centre for Reviews and Dissemination).The protocol was executed according to the following steps:

Inclusion and exclusion criteria
The inclusion criteria were studies evaluating the properties of chickpea aquafaba (technological and nutritional) with no limitations in terms of language or time.The exclusion criteria applied were: (1) reviews, letters, conference abstracts, case reports, books, clinical studies, and review studies; (2) studies that did not evaluate the properties of aquafaba but tried to include it in the formulation of a food product; (3) studies that focused on the improvements of aquafaba through treatments; (4) studies evaluating aquafaba made from other pulses that not chickpeas (e.g., peas, pigeon beans); The excluded studies, and their reasons were inserted as a supplementary file (Table S1).

Information source
Five electronic databases were searched in February 2022: Medline, Embase, Lilacs, PubMed, and Web of Science, complemented by gray literature research in Google Scholar and ProQuest.The reference lists of the selected papers were checked, as relevant studies may have been missed during the data search.

Search strategy
The appropriate combinations of truncation and keywords were selected and adapted for searching each database.The software Rayyan® (Qatar Computing Research Institute-QCRI) was used to aid in the selection and deletion of duplicate articles.The Mendeley desktop software was used to manage all the references (Table S2-Indexers used to select publications that jointly or separately address words related to aquafaba and its properties).

Studies selection and data collection
There were two phases to the study selection process.In phase one, all identified references in the databases had their titles and abstracts reviewed separately by two reviewers (B.B.M, G.S.H).The items that did not match the eligibility criteria were discarded.In phase two, the entire texts of the selected articles were subjected to the eligibility criteria by the same reviewers (B.B.M, G.S.H).In cases of conflict, regardless of the phase, the topic was debated until the two reviewers agreed.In circumstances where there was no agreement, the final judgment was made by a third reviewer (D.C.M).The final decision was always performed after reading the full papers.
The following items were collected in the data collection process: authors and year of publication, research country, the study's objective, the proportion of water and chickpeas, methods, and main results.The report was based on the PRISMA flowchart (Fig. 1).

Risk of bias (RB)
A particular instrument was constructed for this study to evaluate the Risk of Bias using well-established classical and literature criteria and expert guidance, based on instructions provided by the Joanna Briggs Institute (Aromataris and Munn 2021).Six questions were included in the assessment instrument for the bias risk of the chosen 17 studies: (1) Was the Study design appropriate?; (2) Was the statistical analysis adequate to the objective of the study?; (3) Were objective, standard criteria used for measuring the condition?;(4) Did the results answer the main question?; (5) Were strategies to deal with confounding factors stated?; (6) Were the outcomes measured in a valid and reliable way?.When the study received a score of up to 49% "yes," the risk of bias was classified as High, and when the study received a score of 50-69% "yes," the risk of bias was classified as Moderate and Low when the study reached more than 70% yes (Table S3).Exclusion criteria: REASON 1-comments, letters, conference, review, abstracts, papers, and books (n = 8); REASON 2-studies that do not evaluate the properties of aquafaba, but try to include it in the formulation of a product (n = 9); REASON 3-it does not evaluate the properties, but improves aquafaba through treatments (n = 4); REASON 4-studies evaluating aquafaba from different pulses (n = 5);

Results
A total of 1243 articles were initially found in the electronic databases.After removing duplicates, 250 articles titles and abstracts were selected and read.After reading the abstracts, 46 studies were selected for full-text reading.No study records were chosen from the references list of full-text articles.After reviewing the papers, 26 articles were excluded: comments, letters, conference, review, abstracts, papers, and books (n = 8); studies that do not evaluate the properties of aquafaba, but try to include it in the formulation of a product (n = 9); it does not evaluate the properties, but improves aquafaba through treatments (n = 4); studies evaluating aquafaba from different pulses (n = 5) (Table S1-Supplementary material).By the end of the process, 17 studies met inclusion criteria and were considered for this systematic review.The flowchart of the study identification, screening, and inclusion process is in Fig. 1.
About 53% of the studies informed the method used to analyze the protein content analysis.The most frequently (n = 5; 29.38%) used method was the Association of Official Analytical Chemists (AOAC 981.10), which is based on the Kjeldahl Method (Shim et al. 2018;He 2019;He et al. 2019;Landert et al. 2021).The second most used method was the Brad Ford technique (n = 2; 11.76%) (Alsalman 2020;Alsalman et al. 2020a).One study used the Kjeldahl Method without mentioning the correspondent AOAC method (Meurer 2019).Another study used the BCA method (Thermo Sci-entific™, USA) (Buhl et al. 2019a).

Risk of bias (RB)
The studies are heterogeneous, but the majority, 88.23%, had a low risk of bias, 5.88% had a moderate risk of bias, and 5.88% presented a high risk of bias (Table 2).All studies answered the main question.

Studies characteristics
The number of vegetarianism and veganism followers has grown and, consequently, the search for products that can replace food and ingredients of animal origin (Révillion et al. 2020).This growth tendency is mainly found in highincome countries (Leitzmann 2014;Ginsberg 2018).About 10% of the total population declares themselves vegetarians in countries like Australia, New Zealand, Israel, and Sweden.In India, given the prominent religion, one-third of the population is vegetarian (Iguacel et al. 2021).Therefore, following the trend of the recent growth of the vegetarian movement, the studies included in this systematic review topic were conducted recently.

Aquafaba production
Aquafaba can be obtained using two primary sources: homemade cooking of chickpeas wastewater or separating the viscous liquid from canned chickpeas.These different primary sources interfere with the foam capacity and stability properties because of the individual characteristics of the grain, the type of implemented storage (if refrigerated or not) and time of storage, cooking time and temperature, and the use of pressure (Mustafa et al. 2018;He et al. 2019).The homemade process of aquafaba production (Fig. 2) in most of the studies was: the dried chickpeas were soaked for 8-10 h at 4 °C on a proportion of 1:4 (chickpea:water) (He 2019;He et al. 2019;Editors et al. 2021).After that, the water was discarded, and the hydrated grains went into pressure cooking for 30 min on a proportion of 2:3 (hydrated chickpea:water) (Alsalman 2020; Alsalman et al. 2020a;Landert et al. 2021).Subsequently, the cooked chickpeas with the cooking water were refrigerated for 24 h at 4 °C.By the end, the wastewater (aquafaba) was separated from the grains.None of the studies described exactly the protocol displayed in Fig. 2; however, this protocol was constructed based on the most frequent processes in the evaluated studies.

Soaking and cooking processes
Regarding the soaking step, 94.11% of the studies (Mustafa et al. 2018;Shim et al. 2018;Buhl et al. 2019a;He 2019;He et al. 2019;Lafarga et al. 2019a  ) mentioned the proportion of water and chickpeas.The hydration capacity of the grain during soaking is generally related to the physical properties of the grain.Thus, different effects on aquafaba may be noted.A study showed that it was impossible to obtain foam when chickpeas were not soaked (Landert et al. 2021).Soaking is a common process among pulses since the mechanical process of adding water before the cooking process and letting the grains rest underwater for a minimum of eight hours might improve digestion by reducing antinutritional phytates and oxalates while also softening the soaked grain (Fernandes et al. 2010).The hydration promoted by soaking results in the swelling of the seed's cotyledons, making the seed coat crack more permeable (Fernandes et al. 2010;Shafaei et al. 2016).At the same time, the introduced water partially hydrates starch molecules inside the matrix in a rheological phenomenon called gelation (Morris 1990).Combining these processes reduces the cooking time and regulates the chemical diffusion into the cooking water (aquafaba).Some studies mentioned that after soaking and cooking, the total amounts of sugar, oligosaccharides (raffinose, stachyose, verbascose), and protein in chickpeas decreased, given that a part of these compounds was diffused into the cooking water (He et al. 2019(He et al. , 2021;;Alsalman 2020;Alsalman et al. 2020a).Among the compounds diffused into the cooking water, proteins related to aquafaba formation might be more prominent than seeds that skipped the soaking process.Also, it is important to note that most studies discarded the water residual from soaking because of antinutritional compounds (He et al. 2019(He et al. , 2021;;Alsalman 2020;Alsalman et al. 2020a).
The ratio 1:4 (hydrated grains:water) was the most used proportion (n = 5; 29.41%) in the cooking step (Nguyệt 2019; Alsalman 2020; Alsalman et al. 2020a;Editors et al. 2021;Nguyen et al. 2021).However, regarding the technological characteristics of aquafaba, it was not the one with the best results.Therefore, we used the proportion with the best results mentioned in the studies to construct the flowchart (Fig. 2).Although the 2:3 ratio was only tested in three studies, this ratio showed better characteristics, emulsion properties, and foaming capacity in studies that compared it with the 1:4 proportion (Alsalman 2020; Alsalman et al. 2020a).Only one study showed that on the proportion of 1:4 with the pH adjustment with the addition of table salt and citric acid (pH of 4), table salt (3.000 μg mL −1 ) performed the highest foaming ability during the whipping (Nguyen et al. 2021); however, this study did not compare with the aquafaba using the proportion of 2:3 on cooking.
According to a study (Vidal-Valverde et al. 1993), the total sugar content of chickpeas was significantly reduced after boiling in water (32% of reduction).Non-galactoside sugars (fructose and sucrose) decreased slightly more than galactoside sugars (38 and 50% decrease, respectively) (Frias et al. 2000).The solubilization of carbohydrates in water can partly explain these carbohydrate losses during the soaking and cooking process.However, because other water-soluble nutrients were also eliminated, the soluble sugar losses are significantly higher than the percentages shown (Vidal-Valverde et al. 1993).In that case, the aquafaba produced through boiling water could have good foaming stability, given that the solubilization of carbohydrates in the cooking water positively influences aquafaba's foam stability (Vidal-Valverde et al. 1993).
Protein denaturation causes structural changes, which cause protein modifications.These modifications either increase molecule size through aggregation (lower solubility) or decrease it through breakdown into smaller compounds (increased solubility) (Alsalman and Ramaswamy 2021a).As for high-pressure cooking, rupturing non-covalent connections between protein molecules or forming new intermolecular links (such as hydrogen bonds and hydrophobic interactions) promotes protein aggregation].Due to changes in solvation volume, where non-covalent bonds are ruptured and reorganized with solvent molecules, pressure cooking can also increase protein volume (Alsalman and Ramaswamy 2021a).
The different proportions of water seem to affect the technological properties of the aquafaba.Lower quantities of water make the chickpeas soft and crumbly, allowing the starch granules to easily disperse in the cooking water and break the foam membranes, thus lowering the foaming capacity and stability (Editors et al. 2021).Excess water also impairs foam formation by excessive solubilization of starch and protein, thus reducing this compound's concentration (Landert et al. 2021).Regarding refrigeration, according to Landert et al. (2021), this practice, if carried out for 24 h after cooking the beans, significantly improves foam formation and stability.Probably, the cooling time favored chemical reactions such as the starch gelation and extravasation of proteins from the cooked grain to the wastewater.Thus, it results in a greater amount of gelated starch and solubilized proteins, favoring a more technologically stable aquafaba (Landert et al. 2021).

Canned chickpea
The studies that investigated aquafaba from the wastewater of canned chickpeas (Mustafa et al. 2018;Shim et al. 2018;Buhl et al. 2019a) showed that the manufacturers that produced the commercial brands have different genetic chickpea cultivars causing changes in the nutrition composition of the aquafaba, as well as foaming and emulsifying properties (Mustafa et al. 2018;He et al. 2019).In general, the proximate composition of the utilized chickpeas did not influence the stability of aquafaba; nevertheless, it seems that grains with higher amounts of dry matter displayed better emulsion proprieties, resulting in better results for aquafaba (Mustafa et al. 2018;He et al. 2019).Nevertheless, the dry matter content relies mainly on the chickpeas' genotype, given that the aquafaba produced by the "CDC Leader" genotype presented the highest amount of dry matter and, subsequently, the most adequate aquafaba (He et al. 2019).
In addition, some commercial brands include food additives, such as salt, and preservatives like disodium ethylene diamine tetra acetic acid (EDTA), which might suppress viscosity and foam stability by increasing the molecular weight of the formulation (Mustafa et al. 2018;Shim et al. 2018).In this manner, the aquafaba from brands that had no addition of salt or additives produced more dense foam with greater capacity and stability (Mustafa et al. 2018;Shim et al. 2018;Eren et al. 2021).Some food additives, such as citric acid (provided by lime and lemon juices) can be implemented to enhance the stability of aquafaba.A study showed that lowering the pH and decreasing the chickpea:water ratio of manufactured aquafaba improved both foaming and emulsifying capacity of aquafaba (Lafarga et al. 2019b).Other pH-lowering strategies are also successfully improving aquafaba's technological capacities, adding cream of tartar, another acidic ingredient, increased foam and stability (Wong 2020).
Some other studies compared the aquafaba with dried beans (homemade) and canned chickpeas.They concluded that the proportion of 2:3 of homemade aquafaba had the best results, forming foam more quickly and with high stability.The aquafaba from canned chickpeas has a higher foam volume and lower emulsion properties than the homemade cooking conditions, possibly because of the utilized chickpea cultivars; however, these studies did not describe the used chickpea cultivar (Alsalman 2020;Alsalman et al. 2020a;Landert et al. 2021).

Chemical composition
Aquafaba is mainly composed of carbohydrates and protein, but protein is the most evaluated compound in the studies due to its foaming properties (Shim et al. 2018;Buhl et al. 2019a;Alsalman et al. 2020a;Landert et al. 2021;Escadellas et al. 2022).Proteins may present hydrophilic amino acids interacting with water, whereas the hydrophobic amino acids stabilize interactions with the gaseous phase.In this sense, aquafaba foaming capacity strongly correlates with protein content (He 2019).A lack of a standard for protein measurements was observed among studies.Also, some studies showed the content on a dry basis and others on a wet basis.Studies (Shim et al. 2018;Landert et al. 2021) used the same technique for analyzing proteins (AOAC).The only difference in the method is that one of the articles multiplied the nitrogen content by 6.25 and the other by 5.75, probably because the majority of the studies used the general 6.25 factor, and the study that used 5.75 was specific for chickpeas.Despite this, the studies showed different results regarding protein, 1.7% protein for canned chickpeas and 3% protein for homemade chickpeas.The differences in protein content also occur because of the different cooking methods.Boiling can change nutrients' concentrations.There may be solubilization of proteins or even a higher concentration (Lafarga et al. 2019a;Landert et al. 2021).
Only two studies evaluated fat content in chickpea aquafaba, 0.07% (Meurer 2019) and 0.1% on a wet basis [42].This data is important, since fat can influence the foaming capacity of aquafaba.The presence of unsaturated fatty acids reduces the volume and stability of the foam, and chickpea cultivars may contain 2.70-6.50% of fat.It is an important source of unsaturated fatty acids (Behera et al. 2014;Kaur and Prasad 2021).And these two that evaluated fat had lower or higher foaming capacity.
In which regards aquafaba use as a functional ingredient, this plant-based foam was already implemented as a substitute for egg whites in vegan mayonnaises, and in eggless sponge cakes, providing satisfactory results regarding nutritional value, technological and sensory aspects (Mustafa et al. 2018b, Buhl et al. 2019a).Another study analyzed physicochemical and microbiological indicators of aquafaba, and proved that under refrigeration or in the form of dehydrated powder, aquafaba could be used as a viable product, reinforcing its economic value (Ahmed et al. 2021).

Conclusion
This study aimed to evaluate different methods for obtaining aquafaba (soaking type, time, proportion of water or using canned chickpea; use of soaking water; cooking type, time, proportion of water; storage temperature and time; beating time) and compare their nutritional and technological characteristics.The results showed the following steps to prepare aquafaba: soaking for 8-10 h at 4 °C at the proportion of 1:4 (chickpea:water), pressure cooking for 30 min in the proportion of 2:3 (chickpea:water), and refrigerating 24 h/4 °C.Most of the studies used soaking in water as a strategy to homecook chickpeas, improving the diffusion of compounds to the water in the cooking process.The composition of chickpeas did not alter the quality of the aquafaba produced; however, species with higher concentrations of dry matter produced better foam.According to the studies, there was also an indication that aquafaba from wastewater canned chickpeas produced by the CDC Leader chickpeas genotype presented better results regarding foam formation, emulsion capacity, and stability compared to homemade aquafaba.Also, canned chickpeas without added salt or EDTA produced aquafaba with better technological characteristics.

Fig. 1
Fig. 1 Systematic review flowchart adapted from PRISMA.Exclusion criteria: REASON 1-comments, letters, conference, review, abstracts, papers, and books (n = 8); REASON 2-studies that do not evaluate the properties of aquafaba, but try to include it in the formulation of a product (n = 9); REASON 3-it does not evaluate the properties, but improves aquafaba through treatments (n = 4); REASON 4-studies evaluating aquafaba from different pulses (n = 5);