Application of legume‐based materials in encapsulation technology: A review

There has been an increasing global trend for encapsulation of food and pharmaceutical products because of potential roles of this technology in preservation of active ingredients against harsh environments. The food industry ranked after drug sector in the field of encapsulation based on vastness. The delicate bioactive substances are encapsulated using a variety of wall materials. This review article discusses the applications of legume‐based materials for applications in encapsulation technology. The traditional and modern encapsulating techniques are listed. Legume flour, proteins, and starch are effective transporters for the unstable and highly reactive components. Besides physical, biochemical, and chemical modifications of legume‐based proteins and their combinations with polysaccharides are the advanced stages of research. Some functional features of legume proteins have been enhanced by various modifications and combinations with polysaccharides. As a consequence, significant effectiveness has been achieved in encapsulation efficiency. Few active core materials produced from legumes have been effectively enclosed with other wall materials. Furthermore, encapsulated products containing legume wall material have been shown to demonstrate controlled release and increased bioavailability of bioactive components. More research investigations are required to study the health implications of both short‐term and long‐term consumption of these encapsulated products. Legume‐based materials (flour, protein, and starch) possess suitable physical and chemical properties and, as such, offer great potential for commercial use in encapsulation technology.


| INTRODUCTION
There is an increasing global trend toward developing functional foods enriched with bioactive substances possessing potential health benefits.Even with these emerging trends, using direct or free bioactive compounds in foods and nutraceuticals can negatively affect both nutritional value and product quality (Afzaal et al., 2021;Tambade et al., 2020).For example, unfavorable alterations include low stability, poor flavor, and low bio-accessibility (Jansen-Alves et al., 2018).To address such functionality problems, the "encapsulation" technique can play crucial role in resolving these techno-functional challenges (Zhang et al., 2014).The encapsulation process entails entrapping a functionally active core material inside an inert matrix (Karaca et al., 2013).For several years, this technology has been a useful replacement in various industries because it maintains additive efficiency and regulates appropriate medication releases and doses (Sridhar et al., 2022).In recent years, naturally originated substances have received increasing research focus for encapsulation application because they are generally regarded as safe (Afzaal et al., 2021).
A wide range of materials extracted from animals, fish, plants, and microbes are used widely for the encapsulation of various bioactive compounds with demonstrated health benefits (Sharif et al., 2018).In recent years, considerable investigations have been conducted on natural polymers (plant flour, protein, starch, etc.) due to their wide availability, cost-effectiveness, biodegradability, renewable/sustainable features, and their functional qualities (Locali-Pereira et al., 2022;Vázquez-Le on et al., 2021).Legumes have a low GI (glycemic index) of about 30 compared with 100 for white bread used as a standard comparison.They are also loaded with protein, starch, fiber, and plenty of bioactive constituents beneficial for human health.A variety of traditional and innovative processing techniques are used to produce legume-based ingredients with desired techno-functional properties (Keskin et al., 2022).Flour obtained from legume crops is basically a mixture of protein and complex carbohydrates (i.e., starch and fiber fractions) (Locali-Pereira et al., 2022).Legume protein and starch reportedly have convenient thermal properties, emulsifying and foaming abilities, water solubility, film-forming capacities, easy digestibility, and being amphiphilic (Sridhar et al., 2022;Vázquez-Le on et al., 2021).
Owing to these attributes, legume-based materials have emerged as highly suitable materials for wall-forming in the microencapsulation of bioactive compounds for use in the food, feed, pharmaceutical, and cosmetic industries (Nesterenko, Alric, Violleau, et al., 2014).The legume proteins are evident to encapsulate a variety of hydrophilic and hydrophobic bioactive substances and probiotic bacteria (Gharibzahedi & Smith, 2021).The bioactive compounds of legumes can also benefit from encapsulation to minimize degradation from adverse conditions (Traffano-Schiffo et al., 2020).This article presents an overview of the use of legume-based materials and their structural and functional modifications to protect functionally active components by encapsulation technology.In addition, the digestibility of those materials and the encapsulation of legume-based constituents are thoroughly discussed.

| ENCAPSULATION CONCEPT AND TECHNOLOGIES
Encapsulation technology is a proven method for protecting sensitive food and other ingredients from external factors like light, oxygen, and pH (Timilsena et al., 2020).Besides, this technology facilitates a convenient career for the bioactive compounds and ensures the controlled release of the encapsulated cores.Materials that have been encapsulated may be classified into two basic types based on the size, namely, nanoparticles and microparticles.Nanoparticles have a size range of 20-500 nm, whereas microparticles have a size range of 1-200 μm (Afzaal et al., 2021).The bioactive material that is enclosed is referred to as the active core, whereas the core-enclosing material is referred to as the cover, carrier, matrix, shell, or encapsulate (Sharif et al., 2018).
It is noteworthy that there is not a single stabilizing strategy that can be used well in all kinds of food situations.Various methods are used for encapsulation based on the nature of core and coat materials.
Each method has some specific benefits and drawbacks (Gharibzahedi & Smith, 2021).Therefore, the choice of an appropriate approach is dependent on some crucial features, for example, the physical, chemical, and biochemical attributes of the core and shell, the mechanism of contents' release, the intended functional properties, size, stability, cost considerations, and manufacturing techniques (Fuentes-Zaragoza et al., 2011).Materials employed as encapsulants should have high functional and rheological qualities, be suitable for consumption, be biodegradable, be compatible with the active ingredient, be cost-effective, and give optimal stability during and after the manufacture of encapsulated items (Sridhar et al., 2022).
Furthermore, nanotechnology has found application in the food processing industry because of the distinguishable and innovative functional qualities of nanoparticles, including food encapsulation and bioactive food packaging (Gharibzahedi & Smith, 2021).The ultimate result of this approach provides better delivery, and protection, and can entrap a range of bioactive chemicals.Several examples of encapsulation methods employed for legume-based materials are summarized in Table 1.
The fundamental idea behind the encapsulating process is essentially the same for all products prepared from legumes (shown in Figure 1).The components for the core and coat are initially mixed in a solution.In order to generate the ideal environment (e.g., pH, solubility, and stability) for dispersion, required chemicals are utilized in this stage.Occasionally, heat treatments are also used for a predetermined time duration (Karaca et al., 2013;Liu et al., 2014;Mendanha et al., 2009).The mixture is then appropriately mixed or stabilized using a variety of processes, including stirring, homogenization, and micro-fluidization, to create the right working solutions or emulsions (Gharibzahedi & Smith, 2021;Sharif et al., 2018).Several ranges of rotating speed (500 to 20,000 rpm) are used for mixing or homogenization (Jansen-Alves et al., 2018;Kabakci et al., 2021;Karaca et al., 2013;Mendanha et al., 2009).The homogenization method and speed can greatly affect the encapsulation efficiency (Kabakci et al., 2021).Effective stabilization is mainly obtained by microfluidizer or high-speed, high-pressure, and ultrasonic homogenizer (Lu et al., 2021;Teng et al., 2012;Zhang et al., 2014).The final treatment is then administered to produce the finished, capsulated product.The two most commonly used heat treatments to obtain the end product are spray drying and freeze drying.In addition, T A B L E 1 Application of legume-based materials for encapsulation of different bioactive materials.coacervation, emulsification, and evaporation are also employed (Jansen-Alves et al., 2018;Kabakci et al., 2021;Liu et al., 2014;Mendanha et al., 2009;Nesterenko, Alric, Silvestre, & Durrieu, 2014;Teng et al., 2012;Zhang et al., 2014).

| LEGUME-BASED COATINGS FOR ENCAPSULATION
Among field crops, food legumes occupy an important place owing to their production, trade, nutrient-dense nature, and consumption.The global production of legumes has increased significantly in recent years, which offers increasing opportunities for the sustainable production of legume-based materials and fractions.Legume protein and starch are gaining increasing attention with respect to value-added utilization in diverse food applications and non-food uses, for example, as encapsulation material (Afzaal et al., 2021;Pereira et al., 2009).
The functional properties of isolated legume fractions vary significantly with respect to the extraction method used, for example, wet milling produces superior quality fractions as compared with those obtained by dry milling (Keskin et al., 2022).

| Flour
Proteins and polysaccharides essentially make up the majority of encapsulating matrices (Timilsena et al., 2020).Research has revealed that proteins and carbohydrates together exert a stronger impact on emulsion droplets' stability (Sharif et al., 2018).Alternative sources of plant proteins and carbohydrates have been researched as a result of changing eating patterns and an increase in vegetarian/vegan diets.
Varying concentrations of lentil flour were used to encapsulate magnesium with a maximum effectiveness of 97.54%.Smaller particle-size emulsions were produced when the flour content was increased from 15% to 30%, thereby improving the stability of these entrapped particles from 67.6% to 76.0% (Kabakci et al., 2021).Mung bean flour and kidney bean flour are used in conjunction with maltodextrin to encapsulate buriti oil and beta-carotene.These functional compounds are encapsulated using different amounts (5 and 10 g) of both flours in the formulation.The encapsulation efficiency was reported to range from 68.24% to 74.87%, not showing significant variation in performance among the flour-combined formulations (p > 0.05).In another study, bean flours were suggested as a viable option for more sustainable microencapsulation (Locali-Pereira et al., 2022).

| Native proteins
Soy and pea proteins are two of the most important legume-based proteins used for encapsulation.Research has also been conducted on other legumes, such as chickpeas, lentils, and beans (Gharibzahedi & Smith, 2021).Additionally, edible films and coatings based on legume proteins have drawn the significant interest of late, primarily due to their high nutritional value and capacity as carriers of antibacterial, antioxidant, and other bioactive compounds (Sharif et al., 2018).
These proteins are appropriate for encapsulating hydrophilic and hydrophobic bioactive materials (Afzaal et al., 2021).Native legume proteins have been reported to be effectively used to encapsulate a number of substances, including oils, pharmaceuticals, antioxidants, and colors (Sridhar et al., 2022).
The maximum encapsulation and retention efficiencies were found to be 98.7% and 61.71%, respectively, when native legume proteins were used as wall material alone (see Table 1).The highest encapsulation efficiency of 98.7% was observed for soy protein isolate (SPI) encapsulating β-carotene (Yi et al., 2014).Iron was encapsulated using pea protein isolate (PPI) with the highest retention efficiency of 61.71% (Estrada et al., 2018).The encapsulating characteristics of natural legume protein have previously been found to be affected by a number of processing factors, such as homogenizer's pressure level, the temperature of inlet air during drying, core-to-wall percentage, and content of total solids (Tang & Li, 2013).They F I G U E 1 Basic concept and key steps of encapsulation process.
concluded that the core and wall material percentage impart the greatest effects on encapsulation properties.

| Modified proteins
Due to the low solubility, viscosity, and vulnerability to pH, ionic strength, and temperature in comparison to animal proteins, several food processors have abandoned the incorporation of legume-based proteins as wall or shell materials (Tang & Li, 2013).Furthermore, the anti-nutritional factors (ANFs) reduce both the digestibility and bioavailability of proteins and minerals (Sridhar et al., 2022).To address these difficulties, the structure of native proteins is often changed.To address these issues, various modification methodologies, including physical, chemical, and biochemical alterations, or their combinations have been researched (Nesterenko, Alric, Violleau, et al., 2014).
In order to make physical changes, heat, high pressure, sonication, and extrusion can be used to obtain desired results.The most prevalent method for modifying protein structure is heat treatment (Sridhar et al., 2022).Extensive and limited hydrolysis are enzymatic modifications that improve protein's nutritional, medicinal, and functional properties (Afzaal et al., 2021).The first method of chemical modification is the conjugation of low molecular-weight (MW) molecules to protein by acylation, succinylation, esterification, alkylation, or methylation.The second strategy is the conjugation of high MW proteins through the Maillard reaction (i.e., protein-polysaccharides conjugation) (Sharif et al., 2018).The encapsulation and retention efficiency of the SPI varied from 38.3% to 98.68% for various oils and vitamins (as shown in Table 1).Due to the insufficient chain length of wall material to generate a suitably stable structural matrix for enclosing the core material in the case of modified protein, comparably lowefficiency levels were attained (Nesterenko et al., 2012).The use of severe temperature, pH, solvents, and other conditions in chemical modifications produced various regulatory difficulties, which has hampered the food industry's adoption of this technique (Sharif et al., 2018).

| Combined applications
Protein-based emulsions are prone to be affected by pH, temperature, and ionic strength.By contrast, polysaccharides are often more resistant to such changes and build deeper and more-porous and structurally stable interfacial layers (Sharif et al., 2018).Polysaccharides are also more water-soluble and, thus, can withstand a broad range of processing parameters (Keskin et al., 2022).Furthermore, when proteins and carbohydrates are utilized as combined coating materials, they produce microcapsules with increased oxidative stability and drying capabilities (Tambade et al., 2020).The combination may also increase the emulsifying capabilities of proteins, resulting in more stable emulsions (Pereira et al., 2009).As a result, an improved proteincarbohydrate combination is an ideal way for efficient encapsulation (Afzaal et al., 2021).
Lactose, pectin, chitosan, oligofructose-enriched inulin, and maltodextrin are used in conjunction with protein to encapsulate various oils, casein hydrolysates, probiotics, ascorbic acid, and phytase (Sharif et al., 2018).For combined materials, the greatest retention and encapsulation efficiencies were 98.68% and 97.84%, respectively (see Table 1).The retention efficiency of modified protein and carbohydrate combinations was higher than that of the native protein and carbohydrate combinations (Tang & Li, 2013).Legume protein isolate, when combined with two carbohydrates separately, has been shown to significantly reduce the bitterness of encapsulated casein hydrolysates (Gharibzahedi & Smith, 2021).Furthermore, not only native carbohydrates but also modified starch is used as cover material in the encapsulation process.The modified form of starch has benefits such as increased oil load incorporation, increased volatile retention, high encapsulation efficiency, and better shelf life (Tambade et al., 2020).

| Starch
Starch and its derivatives, for example, resistant starch (RS) are frequently employed as wall materials in the encapsulation of different bioactive chemicals, including probiotics (Fuentes-Zaragoza et al., 2011).When compared with cereals (corn, wheat, and rice), legumes often contain a significantly higher content of RS (Keskin et al., 2022).The food industry has recently focused on the production of nano-capsules from starch, primarily due to their superior controlled release characteristics, stability/solubility, bioavailability, and the deliverability of active ingredients in the foods and human body caseinate was investigated for stability.The results indicated that using animal protein as a shell material generated fewer stable microcapsules than using a mix of animal protein and legume starch.Animal protein alone had an encapsulation effectiveness of 79.84%, but when combined with legume starch, its encapsulation efficiency significantly increased to 89.44% (Lu et al., 2021).

| LEGUME BIO-COMPOUNDS AS CORE TO ENCAPSULATE
It is an established fact that encapsulation of bioactive substances is done to protect those from stressful conditions and manage the release of bioactive components from the food matrices in the appropriate location and moment and at the desired rate (Timilsena et al., 2020).In this regard, legume-based bioactives are no different than other health-promoting phytochemicals.
Cowpea pod extract beads had 47% total phenolic compound loading efficiency and 44% antioxidant activity loading efficiency after being encapsulated with hydrogels.Thus, an effective value-added product from legume waste with anticarcinogenic, antihypertensive, anti-inflammatory, and antidiabetic activities may be potentially produced (Traffano-Schiffo et al., 2020).Alginate encapsulated pea flour and starch and efficiently regulated the release of carbohydrates to simulated stomach, intestinal, and fluids in the colon, mainly enrich the slowly digested and resistant starch (SDS, RS) fractions.Pea flour mixed with encapsulated roasted pea starch yielded a better quality pea bread.Both SDS and RS fractions of the bread were shown to increase along with an increase in the starch ratio in the formulation (Lu et al., 2018).

| DIGESTIBILITY AND BIOAVAILABILITY CONSIDERATIONS
The nutrients from meals that are made available to the body during digestion in the gastrointestinal system interact with a range of digestive receptors and body cells (Sridhar et al., 2022).Afzaal et al. (2021) reported that the delivery system efficiency depends on the digestive action of encapsulants, the release mechanism of the encapsulated compounds, and their accessibility.In general, the digesting performance of legume-based proteins as wall materials, the release mechanism of the encapsulated bioactives, and their respective bioaccessibility are intimately related to legume-based component (protein) encapsulation systems.Various legume-protein encapsulation systems were examined to learn more about the impact of the encapsulant on the controlled release of bioactive compounds (Sharif et al., 2018).As a consequence, learning about the digestibility and bioaccessibility of legume protein as a wall material has become an important topic of research for encapsulation applications.-Ferrero et al. (2018) reported that Lactobacillus plantarum and Lactobacillus casei encapsulated with soy proteins showed tolerance to simulated gastrointestinal fluids during in vitro gastrointestinal conditions at 37 C for 8 h in comparison with the control or unencapsulated probiotics.This suggests that soy proteins are capable of conveying the probiotics' physiological activity to the intestine with higher functionality (González-Ferrero et al., 2018).The in vitro gastrointestinal digestion of SPI and acylated soy protein for oral ibuprofen release was studied by Castro et al. (2018).The findings indicated that these proteins could be employed to increase the bioavailability of poorly soluble medications to speed up absorption in the gut (Castro et al., 2018).For in vitro release under stomach circumstances alone and in conjunction with intestinal conditions, flaxseed oil that has been encapsulated with the combination of SPI and modified starch was tested.A study of gastro intestinal settings with flaxseed oil release found that the oil released from the flaxseed oil microcasules under simulated gastrointestinal conditions was 38.24% and it increased to 60.86% when it was heated before digestion (Tambade et al., 2020).To assess nutrients' bioavailability in rainbow trout feed with encapsulated microbial enzyme for salmonid species, phytase from microorganisms was combined with commercial PPI and chitosan.The research concluded that these fish species could better digest the nutrients with legume protein-based diets where microencapsulation was used as an effective delivery system.In comparison to feeds carrying free phytase, the bioavailability of phosphorus in feeds prepared with an encapsulated-phytase was roughly four times higher (Gharibzahedi & Alavinia, 2017).

González
Among the legume proteins, pea protein and lentil protein have superior digestibility, followed by the chickpea protein (Afzaal et al., 2021).Nevertheless, more research is necessary to fully understand the impact of a delivery system's digestive behavior while employing legume proteins from pea, soy, chickpea, and lentil, to name a few.Furthermore, to assess in vivo bioavailability of dietary nutrients and other bioactive compounds, digestion assessment studies utilizing harmonized/validated in vivo digestive models are required (Sridhar et al., 2022).

| CONCLUSIONS
Encapsulation is a widely used commercial technology for develop- Abbreviation: OEI, oligofructose-enriched inulin.

(
Fuentes-Zaragoza et al., 2011).Vázquez-Le on et al. (2021) used black bean starch (BBS) to encapsulate ascorbic acid with a maximal encapsulation efficiency of 36.88%.The starch encapsulates the core material with spherical aggregates, preventing the thermal breakdown of the core during spray drying and allowing for reduced water dispersion.All these mechanisms enhance the stability of encapsulated substance and aid in controlled release.The spherical aggregates of BBS have the potential to be a viable alternative to traditional coating materials used for encapsulation in food applications (Vázquez-Le on et al., 2021).For lutein encapsulation, mung bean starch (MBS) fusion with sodium ing engineered food products, including functional foods with demonstrated health benefits.Encapsulated products made from legume ingredients such as protein, flour, and starch offer several benefits to food processors.The legume-based components have demonstrated notable encapsulation efficiency.Over the last few years, the interest in the functional and stability aspects of these substances, particularly proteins, has increased significantly.The utilization of legume proteins as wall components allows a regulated release of bioactive compounds to the particular target region in the gastrointestinal system, resulting in better bioavailability.Another benefit of using legume-based materials in encapsulation is that consumers are increasingly opting for plant-based products/ ingredients because they are produced in environmentally sustainable agricultural production systems.However, there are certain limitations to using legume proteins as an encapsulant.However, techniques like physical, chemical, and enzymatic changes can be used to overcome these disadvantages in practice.Sometimes a mixture of protein and carbohydrate is used to overcome such obstacles.Finally, further in vitro gastrointestinal investigations and clinical studies are necessary to assess the release mechanism of bioactive compounds in the gut and detect any health-related difficulties that may arise after a long-term use.Nonetheless, legumebased materials offer a cost-effective and sustainable option for encapsulation applications.Commercial production of legume ingredients, for example, novel starches, protein isolates/concentrates, and dietary fibers offers not only healthy food and nutraceutical options for the consumers but also economic return to all stakeholders across legumes' value chain from growers to processors and end users.