Biochemical composition, bioactivity, processing, and food applications of winged bean (Psophocarpus tetragonolobus): A review

Abstract

The winged bean, Psophocarpus tetragonolobus (L.) D.C., is called the four-angled bean or Goa bean, which is an underutilized, non-conventional, and multipurpose tropical legume cultivated in Southeast Asia and Papua New Guinea. The objective of this article was to reveal a comprehensive view on the nutritional properties, biochemical compositions, health benefits, processing, and food applications of winged beans. The average moisture, carbohydrate, protein, fat, crude fiber, and ash content of 138 genotypes of winged bean seeds were found as 9.09 ± 1.73%, 26.81 ± 6.88%, 34.98 ± 4.63%, 18.01 ± 2.27%, 10.24 ± 5.49%, and 4.16 ± 0.41%, respectively. Leaves of winged beans are good sources of vitamins such as vitamin C (14.5–128 mg/100 g), thiamine, riboflavin, niacin, vitamin B₆, folate, vitamin A (5240–20,800 IU), and vitamin E. The seed of winged beans is rich in calcium, iron, phosphorus, zinc, and copper. The anti-nutritional factors, namely, trypsin inhibitor, chymotrypsin inhibitor, phytic acid, saponin, tannin, oxalate, and flatulence saccharides of winged bean, were reported to be in the range of 40–99.5 TIU/mg of protein, 86.4–109.6 CIU/mg of protein, 4.09%–9.96%, 0.6%, 0.77%–0.97%, 0.5%, and 0.04%–0.18%, respectively. This bean can prevent diabetes, cancer, and asthma, boost immunity, and promote women's and men's reproductive health. Winged are transformed into consumable form by processing methods such as soaking, cooking, sprouting, fermentation, roasting, and so forth. This bean is processed into traditional products (curries, soup, pickles, etc.) and contemporary products (milk, tofu, tempeh, etc.). Future research should focus on promoting its utilization as an alternative to soybeans toward meeting global food and nutritional security.

INTRODUCTION

The rapid growth of the world's population has made the nutritional and food security as one of the world's most difficult challenges. To conquer this challenge, a number of approaches are being taken, such as breeding, genetic engineering, microbial production, exploitation of underutilized food sources, and so forth. Out of all approaches, the exploration of underutilized food resources is an environmentally friendly, timely, cheap, and reliable method. The approach to investigating the underutilized food legumes toward food and nutritional security is considered a cheap and reliable method for mass utilization of those legumes. It is very important to evaluate the nutritional, anti-nutritional, toxic, and bioactive components and processing prospects of any under-utilized legume, including winged beans, thoroughly before large-scale utilization to resolve food and nutritional security problems. The winged bean, Psophocarpus tetragonolobus (L.) D.C., is known as the four-angled bean, Goa bean, which is an underutilized, non-conventional, and multipurpose tropical legume crop cultivated in Southeast Asia and Papua New Guinea. This bean crop is termed a “single species supermarket” or “one stalk supermarket,” as all the components of this plant, including pods, immature seeds, flowers, leaves, tubers, and mature seeds, are consumable (Amoo et al., 2006; Lepcha et al., 2017). Its composition and nutritional values are comparable to those of soybeans; hence, it is also known as the “soybean of the tropics.” Winged bean seed is a good source of oil, dietary protein, fat- and water-soluble vitamins, minerals, bioactive compounds, anti-nutritional factors, and toxic compounds (Mohanty et al., 2021). The winged bean is one of the important sources of bioactive compounds such as vitamin C, vitamin E, polyphenols, and flavonoids, which can act as antioxidants. Consumption of winged beans has been shown to have anti-inflammatory, antimicrobial, anticarcinogenic, antitumoral, antimutagenic, anti-allergic, anti-aggregate, and anti-ischemic properties (Khalili et al., 2013; Nazri et al., 2011). Winged bean seeds and parts can be transformed into consumable form by using the processing methods, namely, soaking, cooking, germination, baking, roasting, fermentation, and so forth, which reduce the anti-nutritional factors and toxic compounds and improve the nutritional value. The processing of winged beans is considered essential to produce products such as curries, soups, pickles, milk, tofu, tempeh, and so forth (Lepcha et al., 2017). Being a protein-rich crop, it can alleviate malnutrition and poverty in the developing countries of the world. Before the commercial utilization of winged beans for human consumption, it is very much important to critically examine the biochemical composition of the bean critically, so that processing into products will become viable in terms of nutritional and sensory quality. The winged bean is an important but under-utilized legume that has the potential to resolve the global food and nutritional security problems in the future because of its nutritional potential and multiple uses. Moreover, the information with respect to its nutritional composition, anti-nutritional factors, health benefits, bioactivity, processing, and food uses is scant under a single entity. The objective of this study is to review the nutritional properties, anti-nutritional and bioactive functional compositions, health benefits and bioactivity, processing, and food applications of winged beans. This review study could be helpful to researchers, consumers, cultivators, and policymakers to know its nutritional strength, processing prospects, and potential food uses to induce food security.

MATERIAL AND METHODS

The information and data for this research were gathered by searching review articles, research articles, technical reports, and books on winged beans from 1970 to date. The data were extracted, grouped, and tabulated to align with the study's objective. The grouped data were also analyzed for statistical parameters such as standard deviations, mean, and so forth.

FUNDAMENTAL DOMAIN OF WINGED BEAN

The winged bean, Psophocarpus tetragonolobus (L.) DC., is a dicotyledonous plant, taxonomically falling under the Fabaceae family, Papilionoideae subfamily (Tanzi et al., 2019). Psophocarpus comes from a Greek word that means “noisy fruit.” The winged bean is also known as Goa bean, versatile legume or wonder legume, God-sent vegetable, four-angled bean, princess pea, and four-cornered bean. Winged bean is a self-pollinating crop and has a diploid genome (2n = 2x = 18) of nine pairs of chromosomes (three pairs of short and six pairs of long) with a genome size of 1.22 Gigabase pairs (Harder & Smartt, 1992; Tanzi et al., 2019; Vatanparast et al., 2016). Southeast Asia is considered the origin of this crop due to its long history of cultivation, but the progenitor was supposed to have vanished. Papua New Guinea is considered to be another possible center of origin as large number of large genetic variation exit in this country (Prasanth et al., 2016). It is widely distributed in equatorial countries such as Papua New Guinea, India, Burma, Philippines, Indo-China, China, Malaya, Indonesia, Sri Lanka, Thailand, and in a few Pacific Islands where hot and humid climates exist. The botanical parts of the winged bean are shown in Figure 1. The winged bean is a creeping perennial herb that can grow up to 3–5 m tall. It has green trifoliate leaves and 2.5–3.5 cm flowers that range in color from purple, white, blue, and red. Its roots are tuberous; a tuber ranges in size between 2 to 4 cm in width and 8 and 12 cm in length (Prasanth et al., 2016). The pods are four-sided with fringed wings and have a size of 6–30 cm × 3 cm (length × width), bearing 5–20 seeds per pod (Venketeswaran, 1990). The green pods are tender and contain young seeds, which can be prepared as an excellent vegetable. The mature pod is transformed into wood after dehydration, which contains edible seeds. The dimensions of winged bean seeds are 6.38–8.53 mm, 6.13–7.71 mm, and 5.77–6.85 mm, respectively. The physical properties of winged bean seeds are as follows: sphericity: 0.84–1, thousand-grain weight: 221.76–261.26 g, surface area: 99.60–197.38 mm², bulk density: 843.6–892.03 kg/m³, true density: 1101.89–1238.93 kg/m³, porosity: 24.03%–28% (Mohanty et al., 2015).

FIGURE 1. Different edible parts developed during the life cycle of winged bean.

Winged bean has significant ecological, nutritional, and economic importance in humid tropical areas around the world where soybean farming appears difficult. It is mainly cultivated in equatorial countries such as India, Bangladesh, Thailand, Malaysia, Indonesia, and West Africa, where a relatively hot and humid climate prevails. In India, it is cultivated in northeastern states, Maharashtra, Tamil Nadu, and Kerala, where the humid tropical and subtropical climates prevail. It can be grown up to 2000 m in a variety of well-drained soils with a pH of 5.5 (Mohanty et al., 2013). The presence of Rhizobium bacteria in the root nodules enables growth in low-nutrient soil. In India, the seeds are sown in the months of June–July, and fruits can be harvested after 10–12 weeks of planting. The pod and seed yields are highest in the first year of plantation, whereas the tuber production is highest in the second year of plantation. One single plant can produce 2.5 kg of green pods, 380 g of grains, and 1.07 kg of tubers.

It is one of the vital, underutilized, multipurpose tropical legumes and is grown as a green vegetable, tuber-crop legume, grain, forage crop, and cover crop (Tanzi et al., 2019) All the plant parts, such as young leaves, flowers, tender pods, mature dried seeds, and the tuber of a winged bean, are edible and nutritious. The utilization of edible parts varies according to their geographical regions. The tender pods and young leaves are boiled and used as vegetables, and tubers are boiled, steamed, fried, baked, and used as food. Flowers are used in salads. The dried seeds are steamed, boiled, fried, roasted, and fermented. Mature seeds are used in the production of tempeh, a mold-fermented cake, and milk. The other parts of the plant, including mature leaves, can be fed to livestock animals. Because of its fibrous root system, the winded bean can be used as a cover crop, and it can also be used to improve soil fertility due to nitrogen fixation in its root nodules. It is considered the “soybean of the tropics” because the seed contains analogous proportions of oil, protein, amino acids, minerals, and vitamins as soybeans do. Winged bean is rich in oil and protein and can be utilized as an alternative supplier of vegetable oil and protein in developing countries, which could do much to alleviate malnutrition and poverty in the countries of the Third World. Being protein- and oil-rich crops, they have the potential to be utilized in formulating value-added products, including nutraceutical foods and some pharmaceutically important products.

NUTRITIONAL COMPOSITION Moisture

The moisture content of winged bean grains among the genotypes from different countries differs significantly. The mean moisture content in the winged bean seeds was 9.09 ± 1.73% (Table 1), which indicates that the seed can be stored for a long time. The moisture content in the dried beans is mainly dependent on variety, storage conditions, and the biochemical composition of grains (Adegboyega et al., 2019). The moisture content of other edible parts is above 60%, which indicates that these parts are easily perishable and need to be used immediately after being detached from plants.

TABLE 1 Proximate composition of winged bean seeds.

[Table omitted. See PDF]

Abbreviations: CHO, carbohydrate; GN, genotype number; INPJ, Indonesia, Nigeria, Papua New Guinea, Japan; SNTP, Sri Lanka, Nigeria, Thailand, Papua New Guinea.

Protein

Winged bean seed has higher crude protein content than other commonly used food legumes and is comparable to soybean. The protein content of winged bean seed varied between 27.2% and 45.02% (mean 34.98 ± 4.63%, relative standard deviation [RSD] 13%) among the 139 genotypes. The genotypes grown in Ghana, India, and Malaysia have comparatively low levels of protein in the seed (Figure 2). The other edible parts, such as tender leaves, flowers, green pods, seeds, and the tuberous roots of winged beans, are rich in protein (Table 2).

FIGURE 2. Proximate composition of winged bean from different countries.

TABLE 2 Comparison of nutritional composition of winged bean seeds with other parts.

Parameter	Unit	Flowersa	Leavesa,b	Tender podsa,b,c	Dried seedsa,d,e,f	Tubera,b,c
Proximate composition
Moisture	g	84.2–87.5	64.2–85	76–93	5.3–12.58	54.9–65.2
Protein	g	2.8–5.6	5–7.6	1.9–4.3	27.2–45.02	3.0–15.0
Total lipid (fat)	g	0.5–0.9	0.5–2.5	0.1–3.4	15.2–23.35	0.4–1.1
Carbohydrate	g	3.0–8.4	3.0–8.5	1.1–7.9	14.2–35.66	27.2–30.5
Fiber	g	-	3–4.2	0.9–3.1	1.55–26.15	1.6–17.0
Ash		0.8	1.0–2.9	0.4–1.9	3.52–4.9	0.9–1.7
Minerals
Calcium	mg	300	113–260	53–330	102–850	25–40
Iron	mg	10	2–6.2	0.2–2.3	4.9–16	0.5–3
Magnesium	mg	-	54	58	178–372	23
Phosphorus	mg	500	52–98	26–60	310–637	30–64
Potassium	mg	-	80–460	205–381	100–1090	550
Sodium	mg	-	2.5–18	3.0–3.4	10–50	33
Zinc	mg	-	1.4	0.2	2.6–7.4	1.3
Manganese	mg	-	1.5	2.2	1.9–8.5	10
Copper	mg	-	0.5	0.6	1.1–5.2	1.3
Vitamin
Vitamin C	mg	127	14.5–128	21–37	Trace	26.2
Thiamine	mg	-	3.6	0.06–0.24	0.08–1.7	0.379
Riboflavin	mg	-	2.6	0.08–0.12	0.2–0.5	0.149
Niacin	mg	-	15	0.5–1.2	3.1–4.6	1.64
Vitamin B6	mg	-	1	2	0.1–0.25	0.075
Folate	μg	-	67	-	25.6–63.5	19
Vitamin A	IU	-	5240–20,800	300–900	-	1.3
Vitamin E	mg	-	3.5	0.5	22.8

^aGarcia (1979).

^bOkezie and Martin (1980).

^cMohtar et al. (2013).

^dEkpenyong and Borchers (1980).

^eMutia and Uchida (1994).

^fAverage value from Table 1.

Amino acid profile

Table 3 lists the amino acids found in winged bean edible parts and seed. Among the essential amino acids other than histidine, isoleucine, tyrosine, threonine, and valine were higher in winged bean seed than that found in soybeans (Table 3), while phenylalanine and methionine were lower. The limiting amino acids in winged bean seeds are sulfur-containing amino acids: methionine and cystine.

TABLE 3 Comparison of winged bean amino acid (g/100 g of protein) profile with soybean and egg.

[Table omitted. See PDF]

^aOkezie and Martin (1980).

^bGross (1983).

^cMnembuka and Eggum (1995).

^dRange value of amino acid from Mutia and Uchida (1994), Mohtar et al. (2013), Muhammad and Saari (2014), Mnembuka and Eggum (1995), and Prakash et al. (1987).

^eRange value from Garcia (1979) and Ekpenyong and Borchers (1980).

^fMnembuka and Eggum (1995).

^gFAO.

Protein quality

The quality of protein in raw winged bean seeds can be judged by studying the parameters, namely, protein efficiency ratio (PER), biological value (BV), true digestibility (TD), net protein utilization (NPU), and utilization of protein, which are lower than those of soybean, egg, and casein. The existence of anti-nutritional compounds lowered the protein quality. The anti-nutritional compounds prevent full digestion, and raw bean protein stimulates the fluxing of endogenous fecal N₂ via molting of the intestine's mucosa (Liener, 1994). The value of PER for winged bean's protein held an intermediate position (2.14) within the category of legumes protein (Kantha & Erdman, 1986). The intermediate value of protein quality for winged bean seeds' protein is because of the lower content of methionine and cysteine amino acids. The value of PER for winged bean protein can be enhanced greatly after the adding up of methionine. Further, the in vitro protein digestibility (IVPD) of winged bean protein was lower than soybean.

Protein type

The protein fractions of winged bean seeds proteins are mostly of two types, namely, 7s and 2s; the globular fractions can be further classified into three groups, namely, psophocarpin A, psophocarpin B, and psophocarpin C. The seed storage globulins protein are made up of psophocarpins A and C. Psophocarpin A is a minor component in seed protein and rich in sulfur amino acids. The seed protein of winged bean contained a globulins fraction (7s and 2s) of 6%, which consists of psophocarpin C and psophocarpin B and an albumin fraction of 30 (2s mixture). The psophocarpin B is also present in the anti-nutritional compounds (35%), such as specific chymotrypsin inhibitors, many TIs, and lectins. Out of the total seed protein present in the anti-nutritional compounds and various other compounds, 30% of these proteins are made up of albumin (Kortt, 1979).

Carbohydrate

The average carbohydrate content of winged bean seeds was 26.81 ± 6.88% among 139 genotypes (Table 1). According to Sajjan and Wankhede (1981), winged bean seeds contained 42.2% carbohydrates, 36.2% starch, 2.7% monosaccharides (glucose 1.17% and fructose 1.5%), and 0.61% oligosaccharides (sucrose, raffinose, stachyose, and verbascose). The presence of starch in winged bean seeds was zero (Garcia & Palmer, 1980; Ravindran et al., 1989). Ravindran et al. (1989) reported 37.3%–41.69% non-starch polysaccharides (NSP) in five varieties. The stated NSP was galactose (44.0%–54.9%), arabinose (5.1%–6.5%), xylose (4.3%–6.5%), uronic acid (12.8%–14.3%), and cellulose (17.7%–23.8%), with trace amounts of glucose, rhamnose, and fucose. Out of the total NSP present in the winged bean seeds, it contained carbohydrates (63.2%–67.5%), protein (12.8%–15.2%), lignin (10.4%–12.1%), and ash (3.2%–4.8%) (Ravindran et al., 1989). This distinct NSP composition of mature winged bean seeds may be important in determining sensory, cooking, digestibility, and grain hardness.

Crude fiber

The crude fiber content in 139 genotypes of winged bean seeds varied from 1.52% to 26.15% (Table 1). The fibers are of two types: acid detergent fiber (ADF) and neutral detergent fiber (NDF). ADF and NDF include total cell wall material and cellulose, lignin, respectively. Hemicellulose is determined by subtracting NDF from ADF. The crude fiber of winged bean seeds is as follows: NDF 13.1%–15.6% (mean 14.4%) and ADF 11.3%–12.67% (Garcia et al., 1980). In human health, crude fiber can prevent various chronic diseases such as heart disease, cancer, diabetes, and others. Hence, winged bean flour can be utilized to formulate foods that can alleviate constipation.

Fat

Total crude fat content in the 139 genotypes of winged bean seeds ranged from 15.2 to 23.35 (mean 18.01 ± 2.27%, RSD 13%). The other edible parts, such as the flower, leaves, tender pods, and tubers, contained less than 5% fat (Table 1). The variation in lipid content happened due to different genotypes, locations, environmental conditions, and types of soil where crops were cultivated (Kadam et al., 1984). The crude fat content of genotypes from India, Malaysia, the United States, Nigeria, and Indonesia is less than 20% (Figure 2). In dried seeds, a large portion of lipids accumulates in lipid vesicles, oil bodies, or spherosomes present in the cotyledon (Sathe et al., 1984). The fatty acid profile of winged bean seeds' oil is depicted in Table 4. The lower quantity of linoleic acid (18:2) and linolenic acid (18:3) is reported in winged bean seed oil than in the soya and peanut oil. The oleic acid in winged bean seed oil is higher than the linoleic acid. Soybean oil has a higher concentration of linoleic, arachidic, and behenic acids than peanut oil. The amount of behenic acid in winged bean seed oil is high, but they are not posing any toxicity activity for Indian cultivars. Until and unless the amount of behenic acid seed oil ascertains, one should use oil with great caution (Cerny, 1978). Winged bean seed oil can lower serum cholesterol levels due to the presence of a high amount of linoleic and linolenic acids than animal and milk fat. This oil is less chosen as an edible cooking oil because of its rich saturated fatty acids and unsaponifiable matter than peanut and soybean oils.

TABLE 4 Fatty acid profile of winged bean seeds.

Fatty acids	Immature seedsa	Dried seedsb	Soybean seedsc
Lauric acid (C12:0)	0.3–0.7	0.1–0.9	-
Myristic(C14:00)	0.7–1.3	0.04–0.11	0.06
Palmitic acid (C16:00)	36.27–39.3	5.5–11.9	11.08
Palmitoleic (C16:01)	-	0.2–0.6	-
Heptadecanoic (V17:0)	1.7–2.5	0.1	-
Stearic (C18:00)	13.5–15.5	2.7–7.5	4.894
Oleic (C18:01)	15.3–17.7	25.1–41.01	22.33
Linoleic (C18:02 ω-6)	12.3–14.3	15.28–39.9	54.35
Linolenic (C18:03 ω-3)	3.6–5.2	0.7–4.51	6.007
Arachidic (C20:00)	1.1–1.5	1.1–2	0.5
Ecosenoic (C20:01)	1–1.6	2.3–3.9	-
Behenic (C22:00)	1.8–3	6.22–19.74	0.298
Erucic (C22:01)	-	0.06–1.1	0.319
Lignoceric (C24:00:00)	1.1–1.7	1.4–4.6	0.120
Cerotic (C26:0)	0.3	0.6–1.2	-

^aMohanty et al., 2015.

^bRange value from Higuchi et al. (1982), Homma et al. (1983), Khor and Chan (1988), Bodger et al. (1982), Garcia (1979), and Mohanty et al. (2021).

^cJokić et al. (2013).

Ash and minerals

The ash content of winged bean seeds in 139 genotypes (Table 2) ranged from 3.52% to 4.9% (mean 4.16 ± 0.41%, RSD 10%). Edible parts of the winged bean contained higher amounts of calcium, magnesium, phosphorus, and potassium than the other minerals (Table 2). The winged bean tuber and seeds contained a higher amount of potassium than the other parts.

Vitamins

Both water-soluble and fat-soluble vitamins are found in different edible parts of the winged bean, as shown in Table 2. All edible parts of the winged bean are rich in water-soluble vitamins, but a higher concentration is reported in the leaves than in the other parts (Kantha & Erdman, 1984). The winged bean contains a higher quantity of thiamine, riboflavin, and niacin than soybeans and other beans (Ekpenyong & Borchers, 1980; Garcia, 1979). In winged bean seed oil, γ-tocopherol was revealed to be the dominant form, with a trace amount of α-, β- and δ-tocopherols (De Lumen & Fiad, 1982). The concentrations found ranged from 8 to 130 mg of γ-tocopherol per 100 g of oil, with the majority of samples falling between 23 and 44 mg per 100 g of oil (De Lumen & Fiad, 1982).

ANTI-NUTRITIONAL COMPOUNDS

The anti-nutritional compounds present in winged bean grains are shown in Table 5. The anti-nutritional factors are chemical constituents that adversely affect the enzyme activity, digestibility, nutrition, and health in humans. Similar to legumes, winged bean seeds also contain different types of anti-nutritional compounds, such as protease inhibitors (trypsin and chymotrypsin inhibitors), amylase inhibitors, saponin, phytic acid, tannin, oxalate, and so forth.

TABLE 5 Anti-nutritional factors in dried seed of winged bean.

	Winged bean	Soybean
Anti-nutritional factors
Trypsin inhibitor (TIU/mg of protein)	40–99.5a	65.95–87.09g
Chymotrypsin inhibitor (CIU/mg)	86.4–109.6a	8.28–9.22g
Phytic acid (%)	4.09–9.96b	1.2–1.75h
Saponin (%)	0.6c	4.3i
Tannin (%)	0.77–0.97a	0.072–0.148j
Oxalate (%)	0.5c	0.67–3.5l
Flatulence saccharides (%)
Raffinose	0.18f	3.1–5.7n
Stachyose	0.13f	0.5–0.74n
Verbascose	0.04f	0.12–0.20n
Toxic compounds
Hydrogen cyanide (mg/kg)	21.12–21.18d	0.017–0.035k
L-DOPA (%)	0.35–0.38p	-
PHGA (titer/mg of protein)
A group	94–490e	8.67m
B group	94–480e	8.67m
O group	94–490e	8.67m
Behenic acid (%)	0.7–0.96p	0.298o

Abbreviations: CIU, chymotrypsin inhibition unit; L-DOPA, L-3,4-dihydroxyphenylalanine; PHGA, phytoheamagglutinating; TIU, trypsin inhibition unit.

^aRange value from Ibuki et al. (1983) and Kantha and Erdman (1986).

^bAdegboyega et al. (2019).

^cEsan et al. (2020).

^dSoetan (2018).

^eKotaru et al. (1987)

^fSajjan and Wankhede (1981).

^gBabu and Subrahmanyam (2011).

^hHídvég and Lásztity (2002).

ⁱGupta (1987).

^jMalencic et al. (2008).

^kHonig et al. (1983).

^lMassey et al. (2001).

^mBasir et al. (2010).

ⁿMiddelbos and Fahey (2008).

^oJokić et al. (2013).

^pMohanty et al. (2021).

Protease inhibitors (trypsin and chymotrypsin inhibitors)

TIs hamper the activities of trypsin, or protein-digesting enzymes, which decrease the absorption and utilization of protein and reduce growth. The TIs in winged bean seeds, as stated by different researchers, are diverse in nature. The diverse value of TI is due to the expression unit, the extraction procedure, the concentration, and the nature of the substrate. As a result, determining the concrete value of trypsin inhibition activity (TIA) from the literature is difficult. The TIA of winged bean seeds was measured in trypsin inhibition unit (TIU)/g increments ranging from 15.2 to 9750 TIU/g. The TI of winged bean seeds under the expression unit of TIU/mg of protein ranged from 40 to 50 TIU/mg of protein. Shibata et al. (1986) revealed that the major portion of TIs in winged bean seeds (cv. UPS-31) were Kunitz-type inhibitors, with a small portion of Bowman–Birk-type inhibitors also present. Heat treatment (autoclaving for 15 min) of winged bean seed flour can destroy more than 99% of the TI activity (Khor et al., 1982). Ibuki et al. (1983) also reported that the chymotrypsin inhibitor activity (CIA) of winged bean seeds was 86.4–109.6 chymotrypsin inhibition unit (CIU)/mg. The CIA in winged beans is higher (30–48 mg CIU/g of bean) compared to TI activity (Kortt, 1979). As the chymotrypsin inhibitor of winged beans is mimicked to its TIs, it is grouped as a soybean TI (Kunitz) (Kortt, 1979).

α-Amylase inhibitors

The α-amylase inhibitor (AI) is a proteinaceous compound that binds to the active site of α-amylase to reduce or stop their enzymatic activities, resulting in decrease in starch digestibility. Plant-derived-AI can inhibit the α-amylase activities of mammals, but it cannot inhibit the α-amylase activities of bacteria and fungi (Grant et al., 1995). Most plants produce α-AI to protect themselves by inhibiting the α–amylase activity of insects and animals that prey on plants. The consumption of these inhibitors can act as starch blockers and reduce or stop the starch digestion process, which can further cause symptoms, including diarrhea, nausea, and vomiting. Kotaru et al. (1987) and Grant et al. (1995) showed that the seed of the winged bean is devoid of amylase inhibitor activity (AIA). Sathe et al. (1982), however, discovered AIA in the seed (129.4 AIA × 10⁻³ per protein).

Phytic acid

Phytic acid is considered an anti-nutrient factor because it strongly binds to protein, starch, and mineral and reducing their bioavailability. In the endosperm of winged bean seeds, it remains in phosphate form. The phytic acid content in grains ranges between 0.0025% and 9.96% (Adegboyega et al., 2019; Kantha & Erdman, 1986; Kotaru et al., 1987; Maimako et al., 2022). Phytic acid can prevent HIV by holding back the genomic transcription process in the virus genome. It acts as a preventive agent for the development of kidney stones. It can also prevent plaque, cavities, and tartar in the teeth by reducing the solubility of phosphate, fluoride, and calcium, and protecting them from demineralization.

Saponins

Saponins, also known as plant glycosides, can rupture red blood cells. The amount of saponin present in winged bean seeds is low (0.6%) than in other common pulses (Esan et al., 2020). Saponins have a number of beneficial health effects, including anti-fungal, hypercholesterolemia, anti-inflammatory, anti-parasitic, immunomodulatory, hypoglycemic effects, and so forth.

Tannin

The activity of α-amylase, trypsin, chymotrypsin, and lipase can inhibit by tannin. Tannin also decreases the bioavailability of minerals (iron, zinc, and calcium) (Gilani et al., 2005) and vitamin B₁₂ (Duranti, 2007). The amount of tannin present in winged bean seeds ranged between 0.22 and 51.5 mg/g (De Lumen & Salamat, 1980; Kantha et al., 1986). Tannins have the ability to bind with proteins and thus remove the toxins from the intestine. Tannins can maintain the hygiene of the mouth by preventing the oral bacterial growth that causes tooth decay.

Oligosaccharides

Like other legumes, the winged bean seeds are also composed of indigestible saccharides that cause flatulence, which include the oligosaccharides, namely, raffinose, stachyose, and verbascose. These indigestible oligosaccharides can promote the growth of prebiotic bacteria, such as bifidobacteria, and can be used to develop prebiotic foods. These prebiotic foods have several health-beneficial activities, such as anti-diabetic, anti-cardiovascular, and anti-carcinogenic activity, and they promote higher mineral bioavailability.

Oxalate

The oxalate content in the winged bean ranged from 340 to 597 mg/100 g (Deraniyagala & Gunawardena, 1999; Esan et al., 2020). Oxalate is situated in a separate compartment within the cell in the unprocessed winged bean seeds, but during processing or digestion, it comes out of the compartments and strongly binds with different minerals (calcium, magnesium, potassium, and sodium), which makes these nutrients inaccessible to the body. Oxalate can easily react with calcium and form calcium oxalate, which ultimately results in hypocalcemia. Furthermore, high levels of soluble oxalate in the body can bind with calcium ions, resulting in the formation of an insoluble calcium oxalate complex that aggregates to form kidney stones (Habtamu & Negussie, 2014).

TOXIC COMPOUNDS Lectins

Lectins are proteins of non-immune origin that recognize and reversibly bind to carbohydrates, and precipitate glycoconjugates, and capable of agglutinating blood cells and ribosome-inactivation proteins (Santos et al., 2014). It can also cause nausea, vomiting, stomach upset, and diarrhea. Lectins interfere with the absorption of phosphorus, calcium, zinc, and iron. The seeds of winged beans contain two groups of lectins: acidic lectins (pI = 5.5) and alkali or basic lectins (pI > 9.5), which have erythrocyte hemagglutinating activities. The basic lectins can agglutinate trypsinized human erythrocytes (types A and B) but cannot agglutinate trypsinized human erythrocytes (type O) (Kortt, 1984, 1985). Lectin activity is absent at the early pod development stage but increases significantly at the pod development stage (Yagi et al., 1985).

Hydrogen cyanide

The hydrogen cyanide (HCN) content of winged beans is 170.5–462.8 mg/mL (Maimako et al., 2022). Cyanide is very toxic to humans; even serious intoxication can cause death by blocking the ATP synthesis process involved in the final step of electron transport.

L-DOPA

L-DOPA intoxication occurs in individuals whose erythrocytes are devoid of enzyme glucose-6-phosphate dehydrogenase (G-6-PD). The symptoms of L-DOPA intoxication are nausea, intestinal disorders, anorexia, and vomiting. The seed cake of winged beans contained 0.35%–0.38% of L-DOPA (Mohanty et al., 2021). L-DOPA is a non-protein amino acid that acts as a neurotransmitter precursor and is used to treat Parkinson's disease and related mental disorders.

Toxic fatty acid (behenic acid)

The human digestive system poorly absorbs behenic acid due to its long fatty acid chain. It is proven to be a potential cholesterol-raising fatty acid (Cater & Denke, 2001). The behenic acid content in winged bean seed oil ranged from 6.2% to 19.74%, which is higher than the behenic acid in soybean and peanut oil but lower than the behenate oil (39.5%). Other toxic fatty acids, such as parinaric acid and cyclopropane acid, are low in the Indian variety of winged beans (Mohanty et al., 2021). Although behenic acid is present in winged bean seed oil, it could not pose toxicity as per animal study data. So the seed oil of the Indian winged bean is safe and can be used for edible purposes.

BIOACTIVE COMPOUNDS

Besides nutritional compounds and anti-nutritional factors present in the winged bean, there are presences of various bioactive compounds responsible for various functional properties of the bean. Various chemical compounds, such as phenols, phenolic acids, and flavonoids are produced by the plant cell as secondary metabolites in the different parts of the plants. The chemicals are collectively called plant polyphenols. These plant polyphenols present in the plant extracts exhibit antioxidant activities. Moreover, fruit antioxidant activities are associated with these secondary metabolites as the major responsible compounds (Wang et al., 2018). The primary objectives of these plant antioxidant compounds are to defend the plant cells from oxidative injury to the presence of enzymes and free radicals associated with reactive oxygen (Djordjevic et al., 2011). Mohanty et al. (2013) quantified condensed tannin, along with phenolic acids and flavonoids, in 24 genotypes of winged bean seed. Initially, the plant material was made into a fine powdered form, and extraction was done for the phenolic compounds, and total phenolic content (TPC) was measured using a spectrophotometry method. Further, HPLC chromatogram analysis was performed to quantify individual, naturally occurring phenolic acids, such as ferulic, caffeic, chlorogenic, gallic, protocatechuic acid, and plant flavonoid compounds, such as quercetin, rutin, and kaempferol. It was found that the TPC ranged between 0.09 to 3.49 μg/g, and the kaempferol content in seeds ranged from 1.07 and 790.5 μg/g. Singh et al. (2014) studied the phenolic and flavonoid contents of two types of winged bean plants, such as those grown in the greenhouse and those that are raised from tissue culture. The estimation was conducted for the samples collected from the leaves, stems, and roots of the 6-month-old plants. The quantitative analysis of polyphenolic compounds present in the samples was performed using the HPLC-UV spectrophotometry method. The principal phenolic compounds found in various parts of the winged bean plant were gallic acid, ferulic acid, caffeic acid, chlorogenic acid, protocatechuic acid, and so forth, and major flavonoids found were quercetin, rutin, and kaempferol. It was found that all parts of the plant contained these secondary metabolites, but they varied significantly between the two types of plants grown differently. In another study, Singh et al. (2019) investigated the antioxidant efficacy by determining the total phenol and flavonoid content of 19 genotypes of winged bean. The antioxidant efficacy of the best-performing genotypes was characterized using two chemometric techniques, namely, the agglomerative hierarchical clustering (AHC) and principal component analysis (PCA) method. The amount of total phenol content and total flavonoid contents (TFCs) were found to be 48.4 to 143.5 mg gallic acid equivalent (GAE)/100 g fresh weight and 9.1 to 37.0 mg crude extract (CE)/100 g fresh weight, respectively. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) and Trolox equivalent antioxidant capacity (TEAC) assay methods showed that three of the 19 genotypes were better than other genotypes when it came to antioxidant potentiality. Similarly, Calvindi et al. (2020) also investigated the antioxidant properties of 12 genotypes of winged beans, where they measured antioxidant properties in terms of TFC and TPC. The antioxidant activity was studied through four methods, namely, DPPH assay, ferric reducing antioxidant power (FRAP) assay, Trolox equivalent antioxidant capacity (TEAC) assay, and cupric reducing antioxidant capacity (CUPRAC) assay. Among the tested genotypes, five were recognized to possess significantly high amounts of antioxidant activity in terms of TPC and TFC.

HEALTH BENEFITS OF WINGED BEAN

The seeds and other plant parts have been applied as conventional medicine in many countries for many years. The leaves are used to heal skin sores (boils and ulcers) and smallpox. The roots are used to heal vertigo in Shan states. In New Guinea, the pods and tubers are applied as medicine (Latha et al., 2007). The processed winged beans can increase the high-density lipoprotein and antioxidant and enzymatic activity and decrease the cholesterol and triglycerides in experimental rats (Esan et al., 2020). It can revive severe kwashiorkor diseases (Černý & Addy, 1973). Recent research study proves that the extract of the winged bean plant has several disease-preventing activities such as anti-inflammatory, antimicrobial, antiproliferative, and antioxidant activities (Khalili et al., 2013; Nazri et al., 2011). The antioxidant activity of this bean is because of some major antioxidants like vitamin C, vitamin E, polyphenols, and flavonoids. Phenolic compounds are essential as antioxidants, which show different disease-preventing activities such as anti-inflammatory, antimicrobial, anticarcinogenic, antitumoral, antimutagenic, anti-allergic properties, anti-aggregate, and anti-ischemic. The extract of winged beans has anti-microbial activity (anti-bacterial and anti-fungal) properties. The methanol extract of leaves or roots can eradicate and hinder the growth of Pseudomonas aeruginosa, and Candida albicans (fungus), respectively (Latha et al., 2007; Zuraini et al., 2004). The extract of winged beans has strong anti-proliferative activity. The peptide of winged bean can inhibit the angiotensin-converting enzyme, which results in anti-inflammatory activity (Lee et al., 2011; Mohtar et al., 2013).

PROCESSING OF WINGED BEAN Soaking

The crucial process of soaking winged beans is usually carried out before cooking, germination, dehulling, milk extraction, and fermentation. The eventual usage of a soaked winged bean greatly influences its qualitative attributes. This qualitative trait of soaked grains is primarily influenced by soaking duration, which in turn depends on the grain's capacity to absorb water, the anatomical makeup of the seeds, their size, the soaking medium, the soaking environment, and the moisture level of the grain. When the weight of the beans increased by 80% as a result of soaking, that was the moment at which the soaking process was complete. The kind of soaking solution (1% w/v of NaCl and 0.75% w/v sodium bicarbonate), soaking temperature, and soaking time all affect how long winged beans need to be soaked before cooking. Soaking of winged bean at 40°C in sodium bicarbonate solution significantly reduced the soaking time by about 40% as compared with distilled water soaking at the same temperature.

Cooking

Whole mature seeds are only occasionally used as human food. The mature seeds necessitate a lengthy cooking time (3–4 h), and their consumption causes' abdominal pain, limiting their use. The cooked grains are ground into a paste that can be used to prepare soup after being mixed with other flavoring ingredients. The cooking time depends on the state of maturity. Immature seeds or tender seeds require a short cooking time. In mature or dried seeds, the moisture content is very low, which hardens the seed coat and increases the cooking time. The strong seed coat adhering to the seeds causes slow soaking and prolonged cooking time. The average cooking time of winged beans in the Indian subcontinent is much higher than the average cooking times for traditional legumes in distilled water (Henry et al., 1985). The cooking time of winged beans depends on factors, such as the type of soaking solution, soaking temperature, soaking time, and grain germination (Table 6). Soaking winged beans at 40°C in a 0.75% NaHCO₃ solution for 12 h can reduce the cooking time to 140 min. Soaking germinated grain for 26 h at 20°C can reduce cooking time to 110 min. The cooking time of mature seeds can be decreased to 25 min if the seeds are soaked overnight with 1% sodium carbonate and boiled for 3 min before soaking. Soaking of winged bean or in the suspension of rice husk ash (30 or 50 g/L or in distilled water) for 24 h and then boiling for 30 min cannot soften the bean sufficiently, and the bean cotyledon remained light when boiled in distilled water or rice husk ash suspension. Soaking of winged bean for 24 h in an alkali solution (5 or 10 g/L NaHCO₃10 or 20 g/L baking soda), followed by boiling for 30 min, darkening the cotyledon and producing adequately soft seeds (Buckle & Sambudi, 1990). Kantha and Erdman (1984) developed a quick cooking procedure for winged beans wherein beans are blanched for 2 min, followed by hydration in a mixture of 2% sodium chloride, 0.75% sodium bicarbonate, 1% sodium phosphate, and 0.25% sodium carbonate solutions for 24 h, and finally cooking in boiling water around 15–20 min. The proximate composition, riboflavin, and niacin content were not significantly altered by the quick cooking methods for 18 min compared with the standard cooking time of 210 min for water-soaked beans; however, the thiamine content was significantly reduced by the quick cooking methods compared with the standard water-soaked beans. The processing methods also affected the nutritional properties of the protein. The prolonged heating not only inactivated the TIs but simultaneously reduced the levels of glutamic acid, arginine, histidine, and lysine, which eventually led to non-enzymatic browning reactions, decreasing the protein quality.

TABLE 6 Cooking time of winged beans after various treatments (Henry et al., 1985).

Soak solution	Soak temperature	Soak timea	Cooking timea
	(°C)	(h)	(min)
Distilled water	20	26	200 ± 15
	40	21	200 ± 10
1% NaCl	20	28	240 ± 15
	40	19	200 ± 15
0.75% NaHCO3	20	18	180 ± 10
	40	12	140 ± 5
Germinated beans distilled water soak	20	26	110 ± 15

^aMeans ± s.e.m. for five measurements.

For quick cooking of winged beans, the grains can be soaked for 5 min in the water at 25°C, followed by cooking for 30 min. Quick cooking reduces moisture by 74%, fat by 1.9%, phosphorus by 15.8%, sodium by 43%, magnesium by 61.23%, protein by 13.9%, carbohydrate by 46%, ash by 25%, digestibility by 12%, and potassium by >100% (Ekpenyong & Borchers, 1980). For long cooking of winged beans, the grains can be soaked for 18 h in water at 25°C, followed by cooking for 5 h. Long cooking can reduce the moisture by 48%, the fat by 3.2%, the ash by 16.32%, the phosphorus by 35%, the sodium by 11.4%, the magnesium by 2.8%, the protein by 14%, the carbohydrate by 43.5%, the digestibility by 18%, the calcium by 1%, and the potassium by >100% (Ekpenyong & Borchers, 1980). The moist heat (autoclaving) treatment at 110°C and 15 psi for 30 min can reduce fat by 55%, protein by 2.5%, and ash by 14.2%, and increase moisture by 48%, carbohydrate by 59%, and digestibility by 19% (Ekpenyong & Borchers, 1980). Mutia and Uchida (1994) cracked the bean by passing it through a 0.5 cm screen and autoclaving it at 120°C for 45 min, which reduced the crude fat by 0.9%, the urease index by 94%, TIAs by 87%, protein solubility by 24.4%, and can increase dry matter by 1.63%, protein by 2%, digestibility by 10%, and negatively affect lysine, cystine, and methionine. Cooking winged beans for 4 h at 300°C can reduce the levels of phytate, cyanogenic glycosides, and tannin, but not the antioxidant activity, which is unaffected by cooking (Maimako et al., 2022). Processing treatments, such as autoclaving, infrared, and water boiling can destroy the enzyme inhibitors activity (TI), haemagglutinating activity, and reduce tannins content (Kadam et al., 1984). The cooked winged beans have a nutlike flavor, which is sometimes better than the common bean flavor. Some varieties have acceptable as cooked beans, and even these might not be acceptable to many people because of their new and strong flavor. On the other hand, treatment with sodium bicarbonate softened all beans acceptably and removed bitterness and harsh flavors (Ruberté & Martin, 1978).

Germination

Germination of winged beans is an important practice followed to produce sprouted winged beans, which improves the nutritional attribute of the bean. Soaking of bean at 34°C for 7 h in water followed by draining water and germinating at 36°C for 18 h can achieve 46.25 ± 0.02 mm of sprout length and increase the total phenolic by 997.34 ± 1.14 mg GAE/100 g, the vitamin C content by 124.13 ± 0.01 mg/100 g, and the overall acceptability by 8.94 ± 0.02. Winged bean seeds have a very low rate of germination if stored seeds are used. Germination rates decrease during the first month of storage and reach zero after 6 months. The poor germination rate in winged beans may be because of the very hard seed coat. The same germination rate can be achieved if the seeds are treated with 0.5% KNO₃ at 50°C and 90% H₂SO4 at 60°C (Alex et al., 2010). The germination of winged beans using the between paper technique for 72 h can reduce fat by 1.5%, lipoxygenase activity by 58%, increase the TI by 0.4%, and increase protein solubility by 2.8%. Germination for 48 h decreases the amino acid composition and significantly increases the concentration of aspartic acid, cysteine, and histidine after 72 h (King & Puwastien, 1987).

Fermentation

Fermentation of winged beans is limited, but some researchers use this process for the development of tempeh, pickles, and fermented drinks (Novelina et al., 2013; Phuoc et al., 2019). Winged bean fermentation removes the beany and nutty flavor and improves the eating quality. It also breaks down the nutritional components such as carbohydrates, proteins, and lipids into simple and absorbable forms such as sugar, amino acids, and fatty acids by the action of microorganisms such as yeast, fungi, or bacteria. For the preparation of tempeh, 30 h fermentation is required to get a good quality product. After 30 h of fermentation, there is a significant increase in amino acids and soluble sugar (Kantha & Erdman, 1984). Though the beany flavor can be eliminated after 48 h, there is a complete loss of vitamin C. Fermented drink was prepared from juice from winged bean sprouts by Novelina et al. (2013).

Others processing

Roasting is a dry heat treatment that can be done in a hot oven at 110°C for 30 min. Roasting can reduce moisture by 65%, fat by 4%, protein by 0.8%, ash by 4.2%, and carbohydrate by 74%, but increasing digestibility by 1.3% (Ekpenyong & Borchers, 1980).

FOOD APPLICATIONS

Winged bean is conventional as human food in countries, namely, Southern Asia, South Africa, India, and Malaysia. Being a multi-purpose crop, all the plant parts of winged beans, such as the flower, tender pods, leaves, tubers, and dried seeds, are used to prepare human food. Raw winged bean flowers are eaten after adding them to the salad, fried in oil to develop a mushroom-like taste, and also used as a food coloring agent (Claydon, 1975). The tender pods are used in vegetable salad, whereas the older pods are steam cooked to prepare vegetables and pickles. The leaves have a spinach-like flavor; hence, it is prepared and eaten similarly to spinach. The processing and consumption patterns of winged bean seeds are geographical location specific. In Southern Asia, India, and Malaysia, immature seeds are eaten in soups due to their sweet, nutty taste, whereas mature seeds are eaten after being roasted or dried and ground to produce flour in African countries. Dried winged bean seeds have an unpleasant flavor (rotten smell), which is released because of lipoxygenase activity (Garcia et al., 1980). Tubers of the winged beans are high in carbohydrates and can serve as a stable food source in developing countries; they are consumed after boiling. Roots or tubers have a suitable taste when they are a little thicker than the human thumb. Research and development on winged bean and its product development started around the 1980s in various countries. Such scientific studies include Shurtleff's (1978) study, which described the detailed methods of preparation of various food products, like sprouts, milk, miso, tofu, and tempeh, using winged beans in household conditions. Similarly, Gandjar's (1978) study, reported the development of tempeh by fermenting the winged bean. The processing methods, nutritional and quality characteristics of some winged bean-based food products are discussed below.

Whole bean flour

Sathe et al. (1982) prepared and studied the properties of whole winged bean flour. For the preparation of flour, the whole seeds were ground into powder by using a cyclone mill and then sieved through a 60-mesh sieve to get bean flour (Figure 3). The nutritional composition of whole seed flour is as follows: protein: 39.95%, fat: 17.11%, total sugars: 9.63%, ash: 4.56% (on a dry weight basis), and in vitro protein digestibility: 69.45%. Water absorption capacities, oil absorption capacities, and emulsion capacities of the seed flour were 2.28 g/g, 3.52 g/g, and 71.10 g/g, respectively. The foaming capacity of whole flour was reported as lowered than the soy flour, concentrate, and isolate. The TIA, chymotrypsin inhibition activity (CTIA), AIA, and tannin contents of the bean flour were 283.03, 663.34, 129.40, and 235.00 mg/100 g, respectively.

FIGURE 3. Flowchart for winged beans based processed products [1, 8: Sathe et al., 1982; 2: Kailasapathy & Macneil, 1986; 3, 5: Ruberté & Martin, 1978; 4: Gajanayaka et al., 2021; 6: Mohanty et al., 2021; 7: Makeri et al., 2019; 9: Dench, 1982; 10: Kantha et al., 1983; 11: Phuoc et al., 2019; 12: Novelina et al., 2013; 13: Slamet et al., 1980; 14: Astuti & Agustia, 2011].

Dehulled bean flour

Kailasapathy and Macneil (1986) prepared dehulled bean flour from mature and dried winged bean seeds (Figure 3). For that purpose, the mature and dried seeds were hydrated in water containing 1% citric acid and 1% sodium hydrogen carbonate for the whole night at 27 ± 2°C, followed by boiling for 26–30 min and then removing hulls by using the grain dehuller. To obtain flour, the dehusked beans were blanched at 0°C for 5 min, mechanical-dried at 90°C temperature for 2 h, roasted at 60°C for 5 min, ground in a micro-pulverizer, and sieved through an 80-mesh sieve. Dehulled bean flour can be used to improve the protein content of various bakery products.

Winged bean soup

The winged bean-based soup (Figure 3) was developed by Ruberté and Martin (1978). To prepare winged bean-based soup, the overnight soaked grains were cooked for 4 h followed by grinding the bean with water, oil, wheat flour, commercial spice mixture, and salt in the blender. The ground mixture was boiled for 1 h and served. The sensory quality of winged bean-based soup was found to be better than soybean-based soup. A typical harsh, nutty flavor is found in winged bean-based products that may not be acceptable to every sensory panel.

Cookies and bread

The nutritive quality of cookies can be increased by combining winged bean flour with wheat flour and corn flour. Gajanayaka et al. (2021) used winged bean seed flour and tuber flour to improve the nutritional quality of cookies. For the preparation of winged bean-based cookies (Figure 3), the different composite flours were prepared by mixing seed flour of winged bean (25% to 40%), tuber flour of winged bean (10% to 25%), and corn flour (20% to 40%). The cookies were formulated with 40% of winged bean seed flour, 20% of winged bean tuber flour and 20% of corn flour showed the highest sensory score (7.25) among the formulations. The proximate composition (%) of this cookies formulation was reported as moisture: 2.05 ± 0.29, ash: 4.37 ± 0.02, protein: 16.39 ± 0.58, and fiber: 23.70 ± 0.02. The physical properties of the best cookies formulation were reported as follows: diameter (cm): 4.11 ± 0.06, thickness (cm): 0.07 ± 0.001, weight (g): 4.25 ± 0.18, volume (cm³): 3.68 ± 0.09, density (g/cm³): 1.16 ± 0.06, and spread ratio: 59.28 ± 1.84. Dehulled winged bean flour can be utilized for the preparation of leavened bakery products including bread, to improve their protein content. Replacing 5%–10% wheat flour with flour of winged bean can produce acceptable bread. Kailasapathy and Macneil (1986) developed bread by replacing the 5%–20% wheat flour with dehulled full-fat winged bean flour by using both the straight dough method and the sponge dough method and studied their quality. In straight dough methods, replacing 5%–8% (without the addition of 1% sodium stearoyl 2-lactylate) and 10% (with the addition of 1% sodium stearoyl 2-lactylate) of wheat flour with winged bean full-fat flour produce acceptable bread. In sponge dough methods, replacing 10% (without the addition of 1% sodium stearoyl 2-lactylate) and 12% (with the addition of 1% sodium stearoyl 2-lactylate) of wheat flour with winged bean full-fat flour produces acceptable bread.

Roasted bean snacks

The process for the preparation of roasted winged bean snacks (Figure 3) was described by Ruberté and Martin (1978). To prepare the snacks, the overnight soaked beans are cooked for 3 h, followed by drying to remove surface moisture, and then roasted at 121°C for about 2 h or until they are slightly soft. Roasted winged beans are cooled, seasoned with salt, and served. Winged bean snacks can also be prepared by deep frying technique. In the deep frying process, cooked and surface-dried beans are fried in oil at 177°C temperature for 5–10 min. The snacks developed from the frying process are compared with snacks from soybeans in terms of sensory attributes, such as color, appearance, odor, flavor, bitterness, and overall acceptability.

Winged bean seed oil

Seeds of the winged bean are rich in oil, which can be extracted by using n-hexane or petroleum ether. For extraction of oil, the dried winged bean flour was added into the Soxhlet apparatus, followed by the addition of petroleum ether or n-hexane into it and extracted for 6 h (Figure 3). A rotary vacuum instrument is used to evaporate the solvent from the extract. The extracted oil is dried for 1 h at 103°C before being allowed to cool. The extracted oil can be further packed into bottles. The extracted oil can be further refined to improve its shelf life (Bodger et al., 1982). The refining of winged bean oil can make it safe and fit for human consumption due to the absence of the parinaric and cyclopropene fatty acids and <0.1% of elaidic acid (trans-unsaturated fatty acids [TFA]). In contrast to soybean oil, winged bean's seeds oil is steady during deep frying as the oil contains monounsaturated (39.3%–40.2%), saturated (21.2%–22.7%), and polyunsaturated (37.0%–38.2%) fatty acids. Oil of winged bean upon heated at 110°C for 32 h are not producing any oxidative derivatives and TFA. The quality characteristics of winged bean seeds oil were revealed by Mohanty et al. (2021) as follows: free fatty acid: 0.2%–0.3%, acid value: 0.4–0.6 mg/g, saponification value: 172.2–173.5 mg/g, refractive index: 1.44–1.48, iodine value: 118.9–121.5 g/100 g, and density: 0.91–0.92. Oil is suitable for the preparation of spreads and margarine. Hence, winged bean's seed oil is considered to be healthier oil for frying.

Margarine

Margarine is an alternative to butter and water-in-oil type emulsions in which a discontinuous phase consists of water, salt, flavorings, and preservatives (Arellano et al., 2015; Vaisey-Genser, 2003). The continuous phase is made of oils and holds coloring, antioxidants, and emulsifiers, which are primarily accountable for margarine's texture and consistency. Makeri et al. (2019) developed winged bean oil-based margarine (Figure 3) by blending 50% wing bean oil (WBO), 48.5% palm olein, and 1.5% palm stearin. Winged bean oil-based margarine has good quality and can be used as a table or bakery margarine in tropical countries. It has low thrombogenic indexes and atherogenic, which reduces the risk of coronary heart disease.

Winged bean protein concentrates and isolates

The process for the making of winged bean protein isolates (Figure 3) from winged beans was described by Dench (1982), which have low bulk density, 73%–87% of protein with high fat. The extraction process for protein concentrate (Figure 3) from seeds was described by Sathe et al. (1982), which have 71.5% protein with a lower amount of inhibitors and tannins than whole flour of winged bean (Kantha & Erdman, 1984). As the emulsifying capacity, oil-bearing capacity, and water-holding capacity of winged bean protein concentrate are high, this concentrate can be used to prepare foods where these properties are very important (Makeri et al., 2017).

Tofu

Kantha et al. (1983) developed tofu from winged bean seeds (Figure 3). For the preparation of winged bean tofu, the seeds were soaked in deionized water and dehulled manually. Dehulled beans were blended with boiling deionized water (85–95°C) at a ratio of 1:3 (bean: water) for 3 min. Winged bean milk was separated from the slurry by filtering through eight layers of cheesecloth after discarding the okra. The milk is boiled at 95°C for 7 min with continuous stirring and then cooled to 70°C. The milk was mixed with a coagulant (CaSO₄ [0.5%] 4 mL per 100 mL of milk) and incubated at 70°C for 10 min. After that, the curd was separated from the supernatants. The nutritional properties of winged bean tofu were reported as follows: protein: 9.3%, solid: 16.8%, ash: 0.7%, Ca: 1959 mg/100 g, Mg: 169 mg/100 g, K: 308 mg/100 g, Zn: 5 mg/100 g, and Fe: 7 mg/100 g. Winged bean tofu had a hardness of 13 g (soy 35 g), cohesiveness of 41% (soy 28%), and springiness of 67% (soy 77%). Soya tofu is a light yellow color, whereas winged bean tofu is colorless. Winged bean tofu has more beany flavor than soy tofu.

Winged bean-based pickle

The pickles from winged bean fruit were prepared by Phuoc et al. (2019). For the preparation of pickles (Figure 3), winged bean fruits were blanched at 95°C for 20 s in water containing 4% CaCl_2. After that, the cooled blanched fruits were transferred to a 15% sugar solution and inoculated with Lactobacillus plantarum at 3 × 10⁸ cells/mL. The inoculated fruits are fermented for 15 days. The winged bean pickles are firm in texture and rich in antioxidant activity.

Winged bean-based fermented drink

The preparation process for winged bean-based fermented drinks (Figure 3) was revealed by Novelina et al. (2013). The fermentation drink is prepared from the juice from winged bean sprouts and juice from raw red sweet potatoes. The juice of winged bean sprouts (40%) is combined with the juice from red sweet potatoes (60%) to create the fermentation drink. The quality characteristic of the product as follows: protein: 2.36%; fat: 1.24%; total solids: 18.77%; ash content: 0.23%; Calcium: 0.173%; viscosity: 3.56 DPA, total plate count: 2.1 × 10¹⁰ CFU/mL, and total lactic acid bacteria: 1.9 × 10¹⁰ CFU/mL.

Winged bean kecap

Kecap is an Indonesian word used for soybean sauces, usually popular as a household seasoning agent. The winged bean-based kecap (Figure 3) was developed by Slamet et al. (1980). For the preparation of kecap, the overnight soaked beans are cooked for 3 h. Cooked beans were sliced into tiny pieces, sterilized, cooled, and then inoculated with a spore suspension of Rhizopus oryzae and incubated at 30°C for 72 h. After that, the fermented beans were dehydrated for 48 h at 50°C temperature, followed by soaking in 20% brine for 4 weeks. One kilogram of winged bean seeds yields 4 L of kecap. Winged bean kecap is rich in soluble protein and amino acid content, especially glutamic acid, which contributes to its meal-like flavor. Hence, it is used as a flavoring agent in food industries where meat flavor is required.

Winged bean jam

The jam from winged bean (Figure 3) was developed by Astuti and Agustia (2011). For the production of jam, a water suspension was made from gelling agent pure hydrocolloid (0.85%) and corn starch (2%), heated to 80°C and followed by cooling to 60°C. After that, other ingredients, such as winged bean slurry (25%), suji leaf extract (5%), fruit flavor (0.1%), sugar (10%), salt (1%), cheese (5%), and tween 80 (0.1%) were added to it and then boiled with continued stirring. The prepared jam was hot-filled into glass bottles and sterilized. The quality parameters of winged bean jam are as follows: overall acceptability level: 3.11 (moderately like), spreadability: 3.94 (easy to spread), crude fiber: 2.43%, and vitamin C: 28.75 mg/100 g. This vegetable jam can be applied to bakery products as a filler agent.

FUTURE PROSPECT

The grains of the winged beans are considered to be analogous to soybeans in terms of biochemical composition and nutritional quality; both grains have analogous amounts of oil, essential amino acids, protein, vitamins, minerals, and other constituents. In terms of multiple uses, the winged bean crop is superior to soybean because it can be used for multiple purposes. Being a protein- and oil-rich crop, it is going to be a future crop for the humid tropics to meet food and nutritional security. This multipurpose crop has an immediate need for breeding intervention so as to improve grain yield, cooking quality, and the reduction of toxic and anti-nutritional factors. Although winged bean can be converted into value-added products similar to soybean, due to its unique food matrix composition, it can be used as an agent to improve emulsification and foaming properties. Winged beans should be included in different conventional food products that suit them to improve the nutritional properties and sensory quality. Nutritional supplements or tablets can be prepared from its phytochemical extract for the prevention and cure of chronic diseases. In order to promote its use as a substitute for soybean in meeting global food and nutritional security, future research should employ new processing techniques to improve its nutritional and functional quality.

CONCLUSION

The nutritional properties, anti-nutritional and bioactive-functional compositions, health benefits, processing, and food applications of the winged bean were all thoroughly reviewed in this article. It was found that seeds of the winged bean are a very excellent source of oil (18.01 ± 2.27%), dietary protein (34.98 ± 4.63%), minerals (calcium, iron, phosphorous, zinc, and copper), and vitamins (vitamin C, thiamine, riboflavin, niacin, vitamin B₆, folate, vitamin A and vitamin E, and bioactive compounds). The dominant tocopherol in winged bean seed oil is γ–tocopherol, but there are also trace amount of α-, β-, and δ-tocopherols. Apart from nutritional compounds, winged bean seeds also contain anti-nutritional factors (TI, chymotrypsin inhibitor, phytic acid, saponin, tannin, oxalate, and flatulence saccharides) and toxic compounds (lectins, HCN, L-DOPA, and behenic acid). The research demonstrated that the extract of the winged bean plant has antimicrobial, anti-oxidant, antiproliferative, and anti-inflammatory properties. Processing of this bean could be followed to develop products, such as curries, soups, pickles, salads, milk, tofu, tempeh, dehulled flour, protein isolate, protein concentrate, and jam. Future research should employ new processing techniques to improve its nutritional and functional quality in order to promote its use as a substitute for soybean in meeting global food and nutritional security.

AUTHOR CONTRIBUTIONS

Rejaul Hoque Bepary contributed to the conception and design, manuscript preparation, and critical revision of the manuscript. Arnab Roy was responsible for the manuscript preparation and critical revision of the manuscript. Khanin Pathak was responsible for the manuscript preparation and critical revision of the manuscript. Sankar Chandra Deka involved in the review and finalization of the manuscript. All the authors agree with the content of the manuscript.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the team of Legume Science for selecting our manuscript in the Early Career Researchers' Competition 2022 (Stage 1; Post-Harvest).

CONFLICT OF INTEREST STATEMENT

The authors have no conflicts of interest to disclose.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available on request from the corresponding author.