Value‐Added Processing of Food Legumes Using Extrusion Technology: A Review

Extrusion processing of legumes has gained increased commercial significance in recent years. Food legumes or pulses are a rich source of protein, total dietary fiber, starch, minerals, selected vitamins, and other bioactive compounds with antioxidant activity. The relatively higher protein and lower carbohydrate contents than cereal grains make legumes a healthy choice for developing new food products. While legumes are a staple in many developing countries, their consumption remains to be very low in most of the developed countries. Developing legume‐based ready‐to‐use ingredients and ready‐to‐eat products can potentially increase legume consumption, especially in developed countries. In addition to traditional legume processing methods, extrusion cooking offers a cost‐effective option to manufacture legume‐based products and ingredients. In recent years, increased concerns by consumers about environmental sustainability and food security have resulted in promoting plant‐based proteins as meat substitutes and meat analogs, which are primarily produced by extrusion or wet/dry extraction. In this regard, extrusion is more sustainable and environment‐friendly processing technology due to its process efficiency and minimal effluents. Legumes processed by extrusion cooking have wide applications in a variety of food products, for example, flour mixes and doughs, snack items, baked foods, meat alternatives, meat extenders, gluten‐free products, and nutraceuticals. Furthermore, extrusion process improves the digestibility and functional properties, and lowers or eliminates the antinutrients found in most legumes. This comprehensive review article discusses extrusion processing technology/systems, legumes extrusion, and nutritional quality, functional properties, food safety, and consumer acceptance of extruded legume products.

Food legumes are a staple food in many developing countries but despite their demonstrated nutritional and health benefits, the utilization and intake of food legumes remains to be low in Western countries.However, shifting consumer trends to include more plant-based food options in the diet offers great potential to expand legumes' utilization and consumption in emerging world economies and developed countries (Hill 2022;Uebersax et al. 2023).As pulses, especially common beans, take a long time to cook/prepare (Siddiq, Uebersax, and Siddiq 2022), consumers due to their busy lifestyles prefer convenient, readyto-use, and/or ready-to-eat food options.For example, hummus, a Middle Eastern and North African side dish, has become widely available and consumed in Western countries in recent years.Therefore, new legume-based products must be developed to facilitate increased consumption of legumes, which are not only nutrient dense and healthy but are also produced in an environmentally friendly manner.
In recent years, increased consideration and concerns by consumers about environmental sustainability and nutrition/health focus have helped promote the use of plant-based proteins in meat substitute applications to meet protein requirements (Kinney, Weston, and Bauman 2019).Along with legumes, plant-based protein isolate/concentrate are useful protein substitutes.Legume flour is being investigated as a potential substitute for cereals in extruded goods (Pasqualone, Costantini, and Coldea 2020).Besides traditional technologies and processes, extrusion cooking is a suitable technology to manufacture legume-based value-added products and ingredients.Extrusion processing is relatively more environment-friendly and a sustainable processing technology because process effluents and by-products are minimal.It is noteworthy that the extrusion equipment is generally more cost-effective than the traditional food processing systems.For examples, extruders combinedly perform several unit operations, such as mixing/blending, heating, cooking, expanding, and forming, which significantly increases productivity thereby reducing production costs (Berrios, Losso, and Albertos 2022;Leonard et al. 2020).Pedrosa, Guillamón, and Arribas (2021) demonstrated that the extrusion cooking has a positive impact on the nutritional attributes of legume foods, such as elevated levels of soluble dietary fiber and enhanced preservation of nutritive constituents, taste, and color.Pasqualone, Costantini, and Coldea (2020) emphasized the benefits of the extrusion cooking of proteins and starch, and its effect on nutritional quality, especially, its ability to improve digestibility and lower or eliminate antinutritional compounds normally present in most legumes.
The significance of extrusion in food processing industry is demonstrated in Figure 1.The growing demand for quick meals, combined with increased health consciousness and the nutritional value of pulses, may encourage commercial food producers to provide better food options around the world.If bean-based extruded snacks could take up even 10% of the $16 billion snack food industry in the United States, they may open a $1.6 billion sector that legumes have not yet been able to enter.More importantly, these new goods would provide customers with healthier alternatives as they contain significantly more dietary fiber and protein of existing commercial extruded snacks (Berrios, Losso, and Albertos 2022).Extruded snacks made from legumes have a large market potential and the opportunity to provide customers with healthier choices that are higher in protein and fiber.Asare et al. (2012) demonstrated the possibility of utilizing extrusion processing to process wholesome and nourishing snacks and breakfast items made from legumes.This might help counteract the prevailing market dominance of similar snack products with high caloric value, low in protein, low in fiber, and relatively high in gluten.
This article provides an overview of the use of extrusion for processing legumes, extruded legume products' nutritional quality, antinutritional factors, bioactive compounds, functional properties, consumer acceptance, and food safety in extruded products.
Extrusion technology is primarily a high-temperature-shorttime (HTST) processing method that transforms agricultural commodities into fully cooked products.Extrusion processing has wide applications in breakfast cereal, pet foods, dairy products, baked products, and snacks.The resulting extrudate is low in moisture and considered a generally shelf-stable product (Berrios et al. 2010).During extrusion, enzymes are deactivated, microbial populations are decreased, and nutritional and flavor deterioration are minimized.Extruders can be more economical than conventional technologies because several unit operations can be performed on a single machine, increasing output while lowering expenses (Choton et al. 2020;Prabha et al. 2021).
The extrusion process involves both the heat application and mechanical force simultaneously to shape and form materials, leading to changes in their physical and chemical attributes (Alam et al. 2016).The use of mechanical pressure to force material through an opening, known as a "die," allows shaping products into desired sizes, shapes, and textures.Extrusion cooking is a method of heating food via external heaters besides mechanical friction.Extrusion cooking is a novel and sophisticated food processing technology when compared with batchtype cooking methods and traditional processing, for example, baking.A wide range of puffed products, pallets, granules, or meals may be produced by controlling process parameters such as moisture, high-pressure, high-temperature, and shear-force (Della Valle, Tayeb, and Melcion 1987;Offiah, Kontogiorgos, and Falade 2019).Chinnaswamy (1993) reported that HTST extrusion cooking is used by several food manufacturing sectors to produce expanded snack foods and breakfast cereals (Eastman, Orthoefer, and Solorio 2001).One of these foods' distinguishing characteristics, crispness, is associated with expansion, which is impacted by different extrusion settings (Williams et al. 2010).
The main components of an extruder are shown in Figure 2. Extruder's processing area, referred to as the barrel is divided into three zones: the High Pressure/Forming Zone, the Cooking or Transition Zone, and the Feed/Mixing Zone.Screws are essential components of extruders because they allow feed material to be mixed, kneaded, sheared, uniformly cooked, and conveyed inside the same machine.Extruders can be divided into single-and twin-screw categories.It is believed that General Mills Inc. (USA) was the first to introduce a single-screw extruder in the processing line of ready-to-eat cereals in the late 1930s (Riaz 2000).In the 1960s, as the market for precooked starches and cereals grew, high-throughput extruders that are capable of processing up to product volumes of 10,000 pounds/ hour were developed.Continuous improvements expanded the range of uses for food extrusion processing, enabling a variety of products, including morning cereals, croutons, precooked baby food, and dry pet meals (Berrios, Losso, and Albertos 2022;Prabha et al. 2021).Twin-screw extruders were first used in the food processing sector in the early 1970s, and their use grew quickly.Single-screw extruders are simpler and cost less, but require more processing energy overall.Benefits of twin-screw extruders include increased productivity, uniformity, and process flexibility, as well as the ability to handle a larger range of raw materials.For example, over 16 tons of material may be processed per hour by large twin-screw extruders.Twin-screw extruders are perfect for high-end meals and feeds because the added expense is frequently offset by their multi-functional advantages (Berrios, Losso, and Albertos 2022).
The low-moisture extrusion (typically, < 30%-32%), is a widely used process throughout the food industry, for producing snacks breakfast cereals, and texturized vegetable proteins (Beck et al. 2018;Riaz 2019).By contrast, the high-moisture extrusion, developed in the last two decades, is done at > 40% moisture, and is primarily used to transform vegetable proteins into palatable meat alternatives to mimic meat-like texture and sensory properties (Akdogan 1999;Chen, Wei, and Zhang 2011;Osen et al. 2014).Chen, Wei, and Zhang (2011) studied the effect of lowand high-moisture extrusion on the cross-linking and aggregation of soybean protein.Their results showed that irrespective of the moisture level, hydrogen bonds, disulfide bonds and their interactions together held the structure of protein.However, when moisture level was increased, it increased interactions between disulfide bonds and hydrogen bonds thereby decreasing protein aggregation (Chen, Wei, and Zhang 2011).Both low-and highmoisture extrusion processing can be used to produce valueadded legume-based ingredients for diverse food applications.
Processors can easily make formed extruded products with low-moisture (fully cooked dough or pellets) or low-moisture expanded products (such as fully cooked puffs), depending on variables like temperature, pressure, die size, and geometry.Foods and food ingredients can be cooked in an extruder for 20 to 90 s at 4000-15,000 kPa and die-temperatures of 100°C and 200°C.An extruder system is generally equipped with storage bins, dry-mix feeders, extruder machinery, ports for steaminjection, a die, and a face cutter.Typically, a dryer, a packing system, and a preconditioner unit are incorporated into the system process.Additionally, the integration of computer automation into extrusion production system is incorporated to ensure consistent product quality (Berrios, Losso, and Albertos 2022).To create a variety of extruded products, extruders with variable throughput are commercially available (Table 1).

| Extruded Legume Products
Traditionally, extrusion processing has been used to make ready-to-eat meals from cereal grains like wheat or corn, especially snacks and morning cereals.Products developed through extrusion processing, known as second-generation products, include directly puffed snacks and breakfast-type foods, mainly breakfast cereals.These food products are characterized by their crispy texture and relatively low bulk-density, encompassing a diverse range of recipes, shapes, and formulations.They are transformed into high-protein, dietary fiber-rich, lowcalorie, and gluten-free functional foods for commercialization through enhanced acceptability by consumers (Berrios, Losso, and Albertos 2022;Riaz 2019).Legume flour has been observed to change the textural characteristics of extruded snacks and noodles, indicating the suitability of using extrusion technology to manufacture new functional meals (Miglani, Kaur, and Kaur 2014).The potential use of legumes as in extruded food products is demonstrated by the possibility of low-cost expanded/extrudate products and ready-to-use flour made from de-husked legumes (Balasubramanian, Singh, and Patil 2011).Figure 3 shows legume-based extrusion applications and commercially available extruded products.
Several studies have outlined the extrusion conditions for processing legumes into crisp curls, puffs, and chips, addressing the challenges associated with the process, for example, the need for a potential precooking step and additional drying at relatively high moisture content (Day and Swanson 2013).Additionally, innovative approaches involving the use of legume flours blended with starch and then shaped into facsimiles of the natural raw material have been introduced, indicating the potential for niche-market products (Pedrosa, Guillamón, and Arribas 2021).Furthermore, an extrusion process for creating uniform and highly expanded legume products, including puffy, crunchy snacks with higher protein and fiber content than traditionally available snacks, has been described by Yao et al. (2006).
In addition, according to Adeleye et al. (2020), extrusion processing could improve the consumption of legumes as it improves functional properties of the product.For example, with a decrease in water solubility attributed to protein denaturation during extrusion cooking, ultimately affecting the water solubility of the extruded product (Adeleye et al. 2020).Additionally, it was demonstrated that the extrusion of legumes increases the metabolizable protein value (overall protein digestibility) and improves the quality of the proteins, especially in peas (Solanas et al. 2005).This suggests that the extrusion processing of legumes has the potential to enhance their nutritional value and hence increase demand by health conscious-consumers.
One of the new product development areas where legumes have received a high level of food industry attention in recent years has been plant-based proteins as meat alternatives and non-meat protein ingredients.Mainly, these types of products are manufactured using extrusion technology.Hill (2022) reported that legume proteins are gaining increasing popularity in meat applications, mainly as meat binders and meat extenders.The main reasons for such food applications are to (1) enhance the nutritional profile of the finished product due to added protein and fiber, (2) modify texture by adding legume flour or protein-rich fraction, and (3) replace some allergenic ingredients from other grains commonly used in product formulation, for example, starches and fibers (Hill 2022).Agri-Food Innovation Council (AFIC) had projected that plant-based proteins will account for about 33% of the total protein market by 2024 (AFIC 2019).These patterns have been further confirmed by changing consumer trends, that is, opting for foods produced in an environmentally friendly manner.A 2021 survey showed that 65% of Americans had reported eating "products that attempt to mimic the flavor and texture of animal protein" in the preceding year, and that about one-fifth (19%) had tried legumes as new varieties of plant protein options (IFIC 2021).This survey further reported that the top factors affecting consumers' choices for protein included taste, price, type of protein, and healthfulness.Legumes align well with these market drivers, perhaps with the exception of taste, which can be enhanced through product formulation and culinary variations.
The extrusion processing technology has been at the forefront of producing meat alternatives and meat analogs.These researchers further noted that the processing of meat analogs from plant-proteins is a cost-effective option to satisfy the demand for global protein consumption to feed world's growing population (Guyony, Fayolle, and Jury 2023;Schmid et al. 2022).
A variety of raw materials are used for the development and manufacturing of meat substitutes, for example, soybeans, field peas and chickpeas protein isolates/concentrates besides hempbased proteins, and mushrooms that mimic the texture of beef, chicken, and fish (Berrios, Losso, and Albertos 2022).Kinney, Weston, and Bauman (2019) reported that, in early years, during developmental stages of meat analogs production, the use of low-moisture single-screw extrusion was employed to prepare texturized vegetable proteins (TVPs).The high-moisture extrusion cooking (HMEC), at ≥50% moisture (up to 70%), using twin-screw extruders has become the technology of choice for processing of meat analogs that can match the texture attributes of animal meat (Guyony, Fayolle, and Jury 2023).Berrios, Losso, and Albertos (2022) reported that in the HMEC process, fibrous products are continuously produced (Figure 4) and the optimization of fiber formation requires specific physical transformation and chemical reactions of the proteins, with the process being controlled by variable extrusion parameters.

| Nutritional Properties
Legumes are a nutrient-rich food source, with a rich source of protein, dietary fiber, starch, and minerals/vitamins, as summarized in Table 2 (Hayat et al. 2014;Uebersax et al. 2023).Traditionally, cereal foods derived from cereal grains are the most commonly processed products using extrusion processing.However, as reported by Siddiq, Uebersax, and Siddiq (2022), in comparison with major cereal grains, legumes have relatively higher content of proteins and total dietary fiber while possessing a lower carbohydrates and fat.This nutritional and health benefit of legumes make them suitable for the fabrication of added-value products through extrusion processing.Furthermore, the addition of legume-based ingredients to extruded cereal products could enhance the nutrient profile of the extruded products.
The traditional belief that legumes are unsuitable for extrusion has been challenged, and recent research has highlighted the feasibility of using legumes in extrusion processing (Adeleye et al. 2020 studies have reported that high extrusion temperatures and low moisture levels may have negative impacts on end-product's quality.By contrast, mild extrusion parameters, such as high moisture content and moderate temperature, have been observed to increase the nutritional profile of extruded food products (Singh, Gamlath, and Wakeling 2007).Also, it has been demonstrated how different extrusion processing parameters affect the final product's physical-chemical and nutritional qualities, highlighting the significance of extrusion conditions in assessing the nutritional value of extruded legumes (Costantini et al. 2021).
Extrusion technology for processing of legumes has gained attention due to its potential to bring about nutritional changes in legume-based products.Studies have shown that the textural properties of corn-legume-based extrudates are influenced by processing conditions and raw material characteristics, indicating that extrusion can usually lead to changes in the physical properties of legume-based products (Lazou, Krokida, and Tzia 2010).Furthermore, the die configuration during extrusion can impact the physical and chemical properties, anti-nutrients, and sensory attributes of legume-based extruded snacks, demonstrating the potential for altering the nutritional composition of these products (Costantini et al. 2021).The effect of extrusion processing on the composition and antinutrients is summarized in Table 3. Siddiq et al. (2013) investigated the functional properties of flour from 85°C extruded beans and highlighted the potential of extrusion in modifying the functional properties of legumebased products.Also, the nutritional quality of legume-based extrudates has been investigated, with a particular emphasis on the effect of extrusion processing on the starch and expansion of legume flours (Pérez-Navarrete et al. 2006).And the impact of temperature on the properties of extrudates from high-starch fractions of navy, pinto, and garbanzo beans have been studied and reported (Gujska and Khan 1990).Additionally, legumes fortification and extrusion process had a positive impact on the protein bioavailability and digestibility of wheat-based snacks.This highlighted the potential of extrusion for developing lowfat and low-moisture ready-to-eat products with improved nutritional properties (Patil et al. 2016).
The impact of die configuration on the physicochemical qualities, antinutrients, and sensory aspects of extruded snacks made from legumes has been reported in the literature.For example, how extrusion conditions affect the nutritional and sensory qualities of products made from legumes was studied by (Costantini et al. (2021).Arribas et al. (2017) examined the in vitro digestibility of many rice-legume formulations before and after extrusion to ascertain how extrusion cooking impacted the nutritional content (dietary fiber and in vitro protein digestibility) of the extrudates.Additionally, the digestibility of extruded legume seeds was compared, which showed the potential of extrusion in improving intestinal protein digestibility and concluding that extrusion can lead to better digestion of legume seeds (Solanas et al. 2005).
Pasqualone, Costantini, and Coldea (2020) studied the physicochemical parameters of extrudates containing chickpea flour (CPF) and yellow-pea concentrate (YPC).They reported considerable variations in density of the extrudates depending on their content of CPF and YPC levels (Pasqualone, Costantini, and Coldea 2020).The potential interactions between phytate and elements such as iron, zinc, and calcium were investigated by Galiotou-Panayotou, Kyriakidis, and Margaris (2007) with regard to the bioavailability of these essential minerals, particularly in legumes.Extrusion has been shown to reduce the resistant starch (RS) of all legume starches owing to gelatinization that exposes the starch's whole structure, making it accessible to hydrolytic enzymes.However, after extrusion, the RS content of legume starches showed to be still greater than that of maize starch (Zhang et al. 2016).Furthermore, the impact of extrusion on the physicochemical characteristics and starch digestion kinetics of several legume grains has been studied, offering insight into the impact of extrusion on their nutritional and physiological parameters (Adeleye et al. 2020).The effect of soybean or mung bean addition on the physicochemical and thermal characteristics of extruded instant rice porridge was investigated by Mayachiew, Charunuch, and Devahastin (2015).
The results showed the positive influence of legumes' addition on the properties of extruded porridge (Mayachiew, Charunuch, and Devahastin 2015).
The nutritional characterization of Prosopis laevigata legume tree seed flour, the water absorption/solubility index significantly were shown to change after extrusion, especially, the functional properties of the flour and the impact of extrusion on phytochemicals (Díaz-Batalla et al. 2018).A study on the use of extruded pea seed meal in fish compound diets showed that extrusion did not alter phytic acid or nutritional components, suggesting that extruded legume-based products may retain nutrients (Ramachandran and Ray 2004).The incorporation of legumes in extruded foods has been studied extensively, with a focus on the changes in functional properties and nutritional composition.For instance, the antioxidant activity of legumes has been found to increase during the extrusion process, indicating a potential enhancement of the functional properties of extruded legumes (Pasqualone, Costantini, and Coldea 2020).

| Antinutritional Factors
Legumes contain several antinutritional factors, which impair their digestibility and consumer acceptance.The major antinutritional factors in legumes are lectins, tannins, phytates, and trypsin inhibitors that can reduce the bioavailability of important nutrients.Additionally, legumes have significant concentration of flatulence-causing oligosaccharides (mainly raffinose and stachyose), which are responsible for a negative perception among consumers and their lower consumption rate in spite of the good nutritional value of legumes.However, it has been demonstrated that the extrusion cooking lowers or eliminates all these antinutritional factors in the legume extrudate, improving their acceptability (Kamau, Nkhata, and Ayua 2020).By subjecting legumes to heat, moisture, and mechanical energy during the extrusion process, antinutritional components are denatured and rendered inactive (Adeleye et al. 2020).Additionally, substances that might prevent the digestion of proteins, such as hemagglutinins and trypsin inhibitors, are destroyed because of this process (Kamau, Nkhata, and Ayua 2020).
It has been demonstrated that extrusion cooking inactivates antinutritional factors minimizing their detrimental effect in legumes, which may improve legumes' nutritional value, enhance the bioavailability of vital nutrients, and increase consumer acceptance.By applying heat, shear forces, and pressure, extrusion processing can modify the physical and chemical properties of legume compounds that result in an increase in the nutritional quality.Research has shown that

Nutrients and antinutrient factors
Legume type

Chickpea Pinto bean Faba bean Kidney bean Pea
Total dietary fiber Insoluble dietary fiber Haemagglutinin activity extrusion can denature or denaturize protein inhibitors and other antinutritional components in addition to breaking down complex carbohydrates into simpler ones with more soluble forms (Kamau, Nkhata, and Ayua 2020).Extrusion has also been reported to enhance nutritional quality of legume extrudates by reducing lipid oxidation, gelatinizing starch, and increasing soluble dietary fiber (Singh, Gamlath, and Wakeling 2007).Batista, Prudêncio, and Fernandes (2010) reported that extrusion cooking improves the ability of legumes to emulsify while significantly decreasing antinutrients such as lectin, phytic acid, and alpha-amylase and trypsin inhibitors.The extrusion process also alters the molecular structure of constituents, hence enhancing a food product's nutritional value (Díaz-Batalla et al. 2018).Furthermore, the thermal unfolding of major globulins and thermal inactivation of trypsin inhibitors have been reported to enhance protein digestibility of sulfurcontaining amino acids in legumes (Zaworska-Zakrzewska et al. 2022).Additionally, it has been reported that extrusion significantly reduced lectin activity in terms of phytohaemagglutinin activity (PHA) in light red kidney beans to less than one-tenth of the raw beans (Figure 5).Extruded bean porridge also had acceptable sensory quality, especially for color and texture, when compared with Sosuma, a traditional Rwandan porridge (Nyombaire, Siddiq, and Dolan 2011).Low-temperature (85°C) extrusion was also shown to significantly reduce PHA in navy and pinto beans.However, the effect on oligosaccharides, raffinose, and stachyose was limited (5%-20% reduction) (Kelkar et al. 2012).
Antinutrients present in legumes, such as lectins, trypsin inhibitor, phytic acid, and lipoxygenase, are identical to those present in cereals, demonstrating a shared challenge faced by these factors across plant-based meals (Kong, Li, and Liu 2022).Adding legumes as raw ingredients to cereals during extrusion has shown to modify the physical and nutritional features of the extrudates, indicating the potential for nutritional enhancement in extruded legume-cereal based products (Pasqualone, Costantini, and Coldea 2020).
Extrusion has been demonstrated to improve the bioavailability of micronutrients like iron and zinc in bean extrudates while also lowering antinutritional factors.Overall, the reported studies have demonstrated that extrusion of legumes improves their nutritional qualities by lowering antinutritional factors, increasing protein digestibility, increasing mineral bioavailability, and changing the molecular structures of constituents.Also, these studies indicated the advantage of using extrusion processing to enhance the nutritional value of food products prepared exclusively from legumes or with added legume ingredients, for example, protein or starch concentrates and isolates, and high dietary fiber fractions.

| Bioactive Compounds
In recent years, there has been increased interest in the bioactive properties of proteins and peptides obtained from legumes.Furthermore, as a low glycemic index product, legume starch helps to a gradual release of glucose (Keskin et al. 2021).The bioactive compounds and antioxidant properties of extruded legumes contribute significantly to the nutritional content and health benefits of legume-based products.Pedrosa, Guillamón, and Arribas (2021) reported that the extrusion process influences the bioactive phytochemicals present in legumes, leading to the beneficial effect of the antioxidant activity of the resultant extruded products.These legume phytochemicals, such as phenolic compounds, flavonoids, and isoflavones, contribute to their antioxidant qualities (Lin and Lai 2006;Singh et al. 2020).Díaz-Batalla et al. (2018) reported that the extrusion technique potentially alters the content of bioactive chemicals in legumes, potentially increasing their bioavailability.
Extruded legumes have demonstrated to have protective and health-promoting benefits, highlighting the potential of these products in enhancing general well-being (Rubio, Aranda-Olmedo, and Martín-Pedrosa 2020; Siddiq, Uebersax, and Siddiq 2022).Furthermore, the extrusion processing has been shown to influence the phenolic compounds profile and antioxidant activity of legume-based extrudates, highlighting the possibility of developing functional foods with greater health benefits (Arribas et al. 2019).
Incorporating legumes into extruded goods can also increase fiber content, altering extrudate density (Pastor-Cavada, Martínez-Bustos, and Serna-Saldívar 2013).Furthermore, it has been discovered that the extrusion processing has the potential to limit the loss of bioactive compounds, suggesting the stability of these compounds at high temperatures during extrusion (Rathod and Annapure 2016).Extruded legume-based meals' hydration qualities have also been examined, revealing the possibility of legume flours (e.g., from cowpea, soybean, and groundnut) to be utilized in extruded products (Boye, Zare, and Pletch 2010).

| Functional Properties of Extruded Legumes
The functional properties of food products or ingredients are important from a quality perspective.In this regard, legumes are no exception, as there is a heightened interest in extrusion technology to enhance the functional properties of legumes.An increasing of research has been done recently on the impact of extrusion on techno-functionality of legumes (Cui et al. 2023;Kesselly, Mugabi, and Byaruhanga 2023;Sinaki, Paliwal, and Köksel 2023).Research has indicated that by substituting cereals entirely or in part, legumes provide great potential for the development of extruded ready-to-eat meals (Pasqualone, Costantini, and Coldea 2020).An investigation undertaken by Kristiawan et al. (2018) on the effects of extrusion processing variables on pea flour expansion showed that processing variables have an impact on the expansion of proteinaceous products, including legumes (Kristiawan et al. 2018).The important extrusion processing parameters include moisture content, temperature, and screw speed.Moreover, Patil et al. (2016) have indicated that extrusion of underutilizes legume grains and flours may be used for producing snack food items, thus opening the potential for legumes in snacks.
Among functional properties, the degree of expansion is a critical attribute in the production of food products by using high-temperature/low-moisture extrusion processing.It is a multifaceted occurrence influenced by various factors tied to feed composition and extrusion parameters.Cui et al. ( 2023) investigated the effect of barrel temperature, screw speed, and feed moisture content on expansion in high-quality proteinexpand legume extrudates, including whole faba bean flour and pinto bean flour (Cui et al. 2023).Alvarenga and Aldrich (2019) extruded diets for the fabrication of dry dog food.They reported that by increasing levels of dehulled faba beans in the diet, promoted an improvement in the expansion ratio of the food.Additionally, finer flour particle size and higher extruder screw speeds resulted in greater expansion, highlighting the impact of flour particle size and extrusion conditions on expansion.
According to Brennan et al. (2013), expansion enhances the mouthfeel that is associated with the final product's crispiness, which makes it an essential component of snacks and ready-toeat (RTE) meals.Additionally, the impact of extrusion on legume growth has been investigated in relation to functional and nutritional attributes.Ding et al. (2006) examined how extrusion parameters can impact the functional and physical characteristics of expanded snacks made of wheat, and provided insight into how die swell and extrusion affect expansion.Furthermore, Oliveira et al. (2015) observed an increase in essential amino acids content with added lupine grain to the extrudates, which could impact expansion.
Although the effect of extrusion on the expansion of legumes in the production of food products has been a subject of extensive research (Cui et al. 2023;Ding et al. 2006;Kristiawan et al. 2018;Meng et al. 2010).However, the relationship between extruder screw speed, particle size, and expansion has been a subject of contrasting views, attributed to variations in raw materials, extruder types, and processing parameters.Additionally, the addition of sodium bicarbonate (NaHCO 3 ) was reported to increase expansion ratio of the final extrudate, emphasizing the importance of considering expansion distribution patterns in snack processing (Gat and Ananthanarayan 2015).Meng et al. ( 2010) prepared chickpea flour-based snacks using a twinscrew extruder, achieving a favorable expansion ratio within the range reported for pulses and cereal-based extrudates.This underscored the potential of extruding pulses into nutritious RTE snacks with optimum expansion and texture.
The extrusion effect on the expansion of legumes has also been studied in the context of specific legume types and their processing.Pérez-Navarrete et al. (2006) examining the impact of extrusion on the nutritional quality of blends of maize and Lima bean flour, also determined the effect of extrusion on expansion (Pérez-Navarrete et al. 2006).Furthermore, to gain insight into the effects of replacing legumes on extrudate density and expansion, the physical and nutritional characteristics of extruded products from whole grain with added wild legumes were studied by Pastor-Cavada, Martínez-Bustos, and Serna-Saldívar (2013).
The effect of extrusion on the finished products' physicochemical characteristics is also widely reported in the literature.Research has shown that extrusion greatly increases the water solubility and absorption index (WSI and WAI) of different legume extrudates.This suggests that during the extrusion process, soluble components are released, and starch potentially absorbs more water (Adeleye et al. 2020;Díaz-Batalla et al. 2018;Singh, Rachna, and Sharma 2014).Hashimoto and Grossmann (2003) demonstrated that extrusion processing increases the ability of pasta made from legumes, such as navy, pinto, and common beans, as well as lentil, black gram, and faba bean flour, to absorb water.According to Omwamba and Mahungu (2014), nonstarch polysaccharides have been demonstrated to reduce the quantity of water that evaporates from the sample during the extrusion process, hence enhancing the bulk density (Omwamba and Mahungu 2014).
The functional properties of selected extruded legumes are summarized in Table 4.The functional properties of extruded legumes are affected by various factors, such as composition of raw materials, extrusion processing parameters, and the addition of specific ingredients.Therefore, understanding the impact of these factors on expansion is crucial to producing snacks and RTE foods with desirable texture and mouthfeel.Siddiq et al. (2013) compared the functional properties of navy and pinto bean for baking quality.They compared lowtemperature (85°C) extrusion (EXT) and steam-cooking (STC) flour with those of raw bean flours.It was shown through RVA data that the raw navy bean flour had significantly higher viscosities compared with extruded beans, observed as lower peaks and final viscosities (Figure 6).It is noteworthy that higher pasting temperatures represent a relatively high thermal resistance for the onset of starch gelatinization.As a result, the swelling of the starch granules starts at high temperatures.Whalen et al. (1997) reported that the heat treatment, during extrusion processing facilitates the amylopectin to breakdown enabling it to absorb more water, that is, becoming gelatinized.It was concluded that extrusion improved the overall baking quality as compared with STC or raw bean flours.

| Consumer Acceptance of Extruded Legumes
Given the increased interest in plant-based diets and the continued demand for alternative protein sources, understanding consumer preferences and the acceptability of extruded legumes is critical for product and commercial success.Extrusion technology has been widely utilized for processing of ready-to-eat (RTE) foods because of its efficiency and capacity to produce a range of products with variable textures and shapes/forms that appeal to consumers (Brennan et al. 2013).Consumer acceptability of extruded legumes is a complicated issue that is impacted by different factors, such as processing parameters, nutritional composition, sensory qualities, and health benefits.In addition, research on the effect of extrusion processing conditions on the physical and chemical characteristics of the extruded legumes and their nutritional qualities has drawn increased attention with respect to product development (Pasqualone, Costantini, and Coldea 2020).In this regard, the extruded legume products, besides being shelf-stable, provide consumers with a variety of texture and sensory attributes, which have a significantly impact product acceptability.
Consumers are increasingly opting for nutritious and healthy food products.Extrusion cooking has been demonstrated to enhance the nutritional composition of extruded RTE snacks, with improved total phenolics, total flavonoids, and antioxidant properties, all of which are essential factors affecting customer choices (Brennan et al. 2013).Furthermore, it has been shown that the addition of legumes to rice-based extrudates improves both the bioactive component content and consumer approval of the product.This shows that legume fortification is a potential effective technique for improving the nutritional value and customer acceptance of a food product (Arribas et al. 2019).Proserpio et al. (2020) reported that consumers preferred legume-based snacks (made entirely with chickpea or green pea flour) compared with rice-based types.These researchers further indicated that legumes-based snacks have an added marketing and consumer acceptance advantages as being gluten-free, high in fiber, and nutritious alternatives to traditional cereal-based high-carbohydrate snacks.The studies cited herein underscore the significance of nutritional value and health perceptions of extruded legumes in shaping consumer acceptance.
The critical role that sensory attributes play in shaping consumer acceptability when it comes to food intake cannot be overemphasized.Besides other factors such as cost, convenience, nutrition and health benefits, consumer acceptability of a food product is primarily influenced by its sensory qualities.Hedonic ratings of extruded snacks made from legumes were positively impacted by crumbliness and mild taste characteristics, whereas stickiness, dryness, and hardness had a negative impact on acceptability (Stefanowicz 2013).This signifies the importance of specific sensory attributes in shaping consumer preferences for extruded legume products.Lazou, Krokida, and Tzia (2010) emphasized the importance of taste and sensory perception in consumers' decisions to purchase food, further underscoring the impact of sensory attributes on consumer acceptance.It was further indicated that extrusion temperature can improve the crispness and melting of extrudates, which are important sensory attributes influencing consumer acceptance (Lazou, Krokida, and Tzia 2010).Szczygiel et al. (2017) indicated that extrusion processing could increase the flavor quality and consumer acceptance of navy bean products.Their results showed that extruded bean powder/flour was preferred over commercial flour for production of crackers.The main reason for the preference difference was the presence of lipid-derived compounds that imparted beany, green, grassy, and musty odors in the commercial flour, which were reduced in the extruded flour.These findings further suggest that sensory attributes significantly impact the acceptability of extruded legumes.Moreover, besides the nutritional quality, the functional properties of extruded legumes have been investigated, indicating the potential for innovation and optimization of processing conditions to meet consumer preferences (Olivares et al. 2010).This highlights the need to consider the functional and nutritional characteristics of the extruded legumes in addition to their sensory attributes to improve consumer acceptance.
It is also important to consider that utilizing higher extrusion temperatures and flavoring or coloring may enhance the extruded bean snacks' sensory appeal (Simons et al. 2014).

| Food Safety in Extruded Products
Food safety is a significant concern during the extrusion process.In the last two decades, several foodborne pathogen  outbreaks and recalls have been associated with extruded food for instance, cereal snacks and pet food due to microbial contamination and inadequate processing.Food-borne illnesses caused by Salmonella enterica have been linked often to contaminated legume seedlings (sprouts), including alfalfa, clover, and bean (Jayaraman et al. 2014).For many low-moisture foods, whether cereal-or legume-based types, microbial contamination of extruded products can occur at different stages of the production chain, from raw materials to posttreatment handling and storage.Gastrointestinal infection causing bacteria such as Salmonella and Escherichia coli have been implicated in these incidents (Bianchini et al. 2014;Solís et al. 2022;Verma et al. 2018).A notable foodborne outbreak associated with extruded products was linked to dry extruded pet foods contaminated by the Salmonella serovar Schwarzengrund, which infected 29 human patients between 2006 and 2008 (Behravesh et al. 2010).

Functional property
The process of high-temperature extrusion typically contributes to the inactivation of pathogens.In an oat flour matrix with 0.89 water activity in a single-screw extruder, Anderson et al. (2017) observed > 5-log reductions in Salmonella during extrusion at temperatures > 82°C (Anderson et al. 2017).However, the kind and quantity of microorganisms present, moisture content, process temperature, pressure, screw speed, die design, residence time duration of the extrusion process, and the make-up and characteristics of the extruded products can all affect the degree of microbial reduction occurs.According to Verma et al. (2018), increased fat content a substantial protective impact against Salmonella, while there was a significant negative effect with increasing moisture content.Therefore, it is crucial to validate and control this process to ensure the inactivation of foodborne pathogens (Bianchini et al. 2014;Verma et al. 2018).
Comprehensive food safety procedures must be put in place at all phases of production, processing, distribution, and preparation in order to reduce the risk of outbreaks and recalls involving extruded food items (Stringer and Hall 2007).These consist of regulatory requirements, such as doing routine testing for microbiological pollutants, and using adequate sanitation techniques (Bianchini et al. 2014;Qiu, Li, and Li 2021;Solís et al. 2022;Verma et al. 2018).Additional research and development initiatives are required to enhance the quality and safety of food items that are extruded, including the addition of beneficial ingredients and the optimization of processing factors for a maximum retention of bioactive compounds (Choton et al. 2020).
Additionally, recalls of extruded food products have also been caused by non-microbial contamination and foreign materials, including veterinary drug contamination and adulterated ingredients, that have not been disclosed (Carrión and Thompson 2014).These occurrences demonstrate how crucial it is to follow labeling guidelines and implement quality control procedures in order to guarantee the integrity and safety of these items.It is also important to note that during postextrusion handling and storage, workers, equipment, packing materials, and the environment can all cross-contaminate foods that have been safely extruded.Thus, to preserve the microbiological safety and shelf life of extruded products, appropriate cooling, drying, packaging, and storage conditions are crucial (Anderson et al. 2017;Verma et al. 2018).

| Summary
Legumes are an excellent source of several nutrients, including proteins, dietary fiber, minerals, vitamins, and antioxidants.Incorporating beans into meals on a regular basis can provide several physiological advantages that support well-being and potentially prevent or lessen the effects of certain metabolic illnesses.In recent years, there has been an increased demand for plant-based proteins as meat alternative applications, including meat analogs, to meet protein demands.These trends have emerged due to consumers' heightened concerns about environmental sustainability and an increased focus on nutrition and healthy food choices.Compared with traditional processing methods, extrusion, characterized by a high-temperature, short-time processing, stands out as an inventive and cuttingedge food processing technology.Extrusion processing has been shown to improve the nutritional profile (increased digestibility and decreased antinutrients), functional properties, and sensory attributes.In addition, extruded legume products have a stable shelf-life with minimal food safety concerns.It is noteworthy that consumer acceptance of extruded legumes is determined by a variety of parameters, including processing conditions, nutritional content, sensory qualities, and health perceptions of the products.Comprehending and tackling these variables is vital for the efficacious creation and promotion of extruded snacks made from legumes.

TABLE 1 |
Specifications and capacities of commercial extruders for processing different extruded products.

TABLE 2 |
Nutritional composition of selected legumes in comparison to wheat and maize (per 100 g basis).Data are average of four major common bean classes (pinto, navy, red kidney, and black beans).
a b Dietary folate equivalent.

TABLE 4 |
The effect of extrusion processing on the functional properties of selected legumes (↑ = increase; ↓ = decrease; ↕ = mixed trend).