adzuki beans

What are adzuki beans

Adzuki bean (Vigna angularis L.), sometimes called small red beans (approximately 5 mm) or English red mung bean, is a dietary legume crop in East Asian countries like China, Japan, and Korea as an ingredient for traditional dessert cuisines due to its sweet taste, as well as its nutritious protein and starch contents 1). Consumption of legumes potentially reduces the risk of chronic diseases 2) such as stroke, type II diabetes 3), cardiovascular 4), and gastrointestinal cancer 5). In addition to fiber, legume grains also contain many substances to improve health such as vitamins, minerals, and other substances, including phenolic compounds 6). The annual cultivation area for adzuki bean in China, Japan, Korean peninsula, and Taiwan is estimated to be 670,000, 120,000, 30,000, and 20,000 hectares, respectively 7). The wild species of adzuki bean such as Vigna angularis var. nipponensis, Vigna nakashimae, and Vigna nepalensis, are widely distributed across East Asia and Himalayan countries 8). However, archaeological evidences suggested multiple domestication origins in northeast Asia 9). The Adzuki bean cultivars most familiar in Northeast Asia have a uniform red color, however, white, black, gray, and variously mottled varieties also are known.

The predominant use of adzuki beans in traditional Japanese confections is a paste or wagashi such as youkan, manju and amanatto 10). Adzuki beans are a rich source of carbohydrates, protein, vitamins, minerals and fiber 11); however, adzuki beans also contain antinutritional factors 12). Antinutritional factors are substances that when present in human foods or water reduce the availability of one or more nutrients. Phytates, α-galactosides and trypsin inhibitors are among these antinutritional factors, and their concentrations differ widely among the different cultivars of adzuki beans. Therefore, when adzuki beans are used for confectionaries, they are boiled in a cooker and yield a hot water extract as a by-product, which is known to contain active ingredients, but is discarded. It has been reported that the 40% (w/v) ethanol fraction of the hot-water extract from adzuki beans suppresses not only proliferation of human stomach cancer cells in culture but also benzo(α)pyrene-induced tumorigenesis in the mouse fore-stomach 13). Thus, the hot-water extract of adzuki beans has a number of effects according to studies in animals (e.g., rats) 14). Thompson et al. 15) have reported that polyphenols and phytic acid have potential hypoglycemic activity. A study in rats with with streptozotocin induced diabetes show that adzuki bean paste produced by boiling adzuki beans has inhibitory activity against alpha-glucosidase, alpha-amylase, maltase, sucrase, and isomaltase 16). The adzuki bean paste showed potential hypoglycemic activity in both normal mice and streptozotocin (STZ)-induced diabetic rats after an oral administration of sucrose, but did not show any effect on the blood glucose concentration after glucose administration, suggesting that the active fraction suppressed the postprandial blood glucose level by inhibiting alpha-glucosidase and alpha-amylase, irrespective of the endogenous blood insulin level. Wu et al. 17) have shown recently that a water-soluble extract of the adzuki beans could inhibit acetaminophen-induced liver damage. Han et al. 18) have reported the protective action of an adzuki extract against acetaminophen-induced hepatotoxicity via a hepatic γ-glutamylcysteinylglycine-mediated antioxidation/detoxification system in rat liver after four weeks of feeding.

Figure 1. Adzuki beans

adzuki beansFigure 2. Black adzuki beans

Black adzuki beans

Adzuki beans nutrition

Cooked adzuki beans are 66% water, 25% carbohydrates, including 7.3% dietary fiber, 8% protein, and contain negligible fat. In a 100 gram amount, cooked beans provide 128 Calories. Adzuki beans contain a moderate to high content (10% or more of the Daily Value, DV) of the B vitamin folate (30% DV) and several dietary minerals (11% to 27% DV).

The fatty acids compositions of total lipids and phospholipids in the adzuki beans were compared among the five cultivars (data not shown). The low total lipid contents of adzuki beans is similar to other foods – cereals as rice and rye, and legumes as bean, chick-pea and beans, that have less than 2% of fat, but with the advantage that the fat of the adzuki bean possesses a healthy Polyunsaturated fatty acids (PUFAs) omega-6/omega-3 which are essential fatty acids for human nutrition. Adzuki beans has good amounts of total unsaturated fatty acids which consisted mainly of linoleic (18:2n-6) acid, followed by α-linolenic (18:3n-3) and oleic (18:1n-9) acids, representing 70.6-73.8 wt-% and 69.9-72.6 wt-% for total lipids and phospholipids, respectively.

Table 1. Adzuki beans (mature seeds raw) nutrition facts

NutrientUnitValue per 100 g
Total lipid (fat)g0.53
Carbohydrate, by differenceg62.9
Fiber, total dietaryg12.7
Calcium, Camg66
Iron, Femg4.98
Magnesium, Mgmg127
Phosphorus, Pmg381
Potassium, Kmg1254
Sodium, Namg5
Zinc, Znmg5.04
Copper, Cumg1.094
Manganese, Mnmg1.73
Selenium, Seµg3.1
Vitamin C, total ascorbic acidmg0
Pantothenic acidmg1.471
Vitamin B-6mg0.351
Folate, totalµg622
Folic acidµg0
Folate, foodµg622
Folate, DFEµg622
Vitamin B-12µg0
Vitamin A, RAEµg1
Vitamin A, IUIU17
Vitamin D (D2 + D3)µg0
Vitamin DIU0
Fatty acids, total saturatedg0.191
Fatty acids, total monounsaturatedg0.05
18:1 undifferentiatedg0.05
Fatty acids, total polyunsaturatedg0.113
18:2 undifferentiatedg0.113
Fatty acids, total transg0
Amino Acids
Aspartic acidg2.355
Glutamic acidg3.099
Total isoflavonesmg0.58
Biochanin Amg0
Proanthocyanidin dimersmg19.4
Proanthocyanidin trimersmg18.1
Proanthocyanidin 4-6mersmg80
Proanthocyanidin 7-10mersmg75.7
Proanthocyanidin polymers (>10mers)mg252.9
[Source: United States Department of Agriculture Agricultural Research Service 19)]

Table 2. Adzuki beans (mature seeds cooked or boiled without added salt) nutrition facts

NutrientUnitValue per 100 g
Total lipid (fat)g0.1
Carbohydrate, by differenceg24.77
Fiber, total dietaryg7.3
Calcium, Camg28
Iron, Femg2
Magnesium, Mgmg52
Phosphorus, Pmg168
Potassium, Kmg532
Sodium, Namg8
Zinc, Znmg1.77
Copper, Cumg0.298
Manganese, Mnmg0.573
Selenium, Seµg1.2
Vitamin C, total ascorbic acidmg0
Pantothenic acidmg0.43
Vitamin B-6mg0.096
Folate, totalµg121
Folic acidµg0
Folate, foodµg121
Folate, DFEµg121
Vitamin B-12µg0
Vitamin A, RAEµg0
Vitamin A, IUIU6
Vitamin D (D2 + D3)µg0
Vitamin DIU0
Fatty acids, total saturatedg0.036
Fatty acids, total monounsaturatedg0.009
18:1 undifferentiatedg0.009
Fatty acids, total polyunsaturatedg0.021
18:2 undifferentiatedg0.021
Fatty acids, total transg0
Amino Acids
Aspartic acidg0.891
Glutamic acidg1.173
[Source: United States Department of Agriculture Agricultural Research Service 20)]

Adzuki beans health benefits

Adzuki bean is a very important bean in the East Asia. Adzuki bean is used as a diuretic, antidote, and remedy for edema and beriberi in traditional Chinese medicine 21) and being prescribed for infection and inflammation of the appendix, kidney and bladder 22). Water and methanolic or ethanolic extracts of azuki bean have been demonstrated to up-regulate inducible nitric oxide synthase (iNOS) and to reduce blood pressure 23), decrease serum cholesterol levels 24) and ameliorate diabetes progression 25). Azuki bean seed coats, which are rich in polyphenols, were recently reported to attenuate vascular oxidative stress in spontaneously hypertensive rats 26). However, little is known about the molecular mechanisms of the beneficial effects of azuki bean. To date, only one study has reported the immunomodulatory mechanism of azuki bean extract: an ethanol extract inhibited nuclear factor (NF)-κB, activator protein (AP)-1, and cAMP response element-binding protein (CREB) activation in lipopolysaccharide (LPS)-, poly(I:C)- and pam3CSK-activated macrophages and blocked the activation of the upstream signalling molecules, including p38 and TAK1 27). Blockade of IL-6 activities with tocilizumab (anti-IL-6 receptor antibody) has been reported to significantly reduce disease activity in rheumatoid arthritis, indicating that IL-6 is strongly involved in the pathogenesis of rheumatoid arthritis 28). This study 29) showed that the inhibitory activity of adzuki beans on IL-6 signalling was associated with an anti-rheumatic effect by using a collagen-induced arthritis mice model. Oral administration of adzuki beans extract suppressed tissue damage occurring in collagen-induced arthritis. The adzuki beans extract triterpenoids — oleanolic acid and oleanolic acid acetate— have the potential to be an effective treatment for rheumatoid arthritis, but requires furhter investigation and studies in order to be considered for rheumatoid arthritis treatment.

Polyphenols are plant secondary metabolites and have attracted interest with health benefits 30). Genistein, a polyphenol compound, belongs to the category of isoflavones, and has been found almost every leguminous plants including adzuki beans (Figure 3). Early studies indicated that genistein protects age-associated degenerative disorders such as myocardial infarction (heart attack) 31), hepatic failure 32), diabetes, obesity 33) and brain damage 34). In addition, genistein proved to be effective in neuroprotection and bone loss in animal models via estrogen-mimicking activity 35).

Figure 3. Adzuki beans genistein

Adzuki beans genistein
[Source 36)]

Phenolic compounds are resistant to oxidation and protect cell damage to prevent the risk of degenerative diseases thanks to antioxidative, anti-inflammatory, antiallergic and anticarcinogenic activities 37). There were 11 phenolic constituents identified in adzuki beans 38). Total phenolics are naturally produced during the growth and development of plants to protect themselves from biotic stresses such as diseases, insects and environmental stresses 39). Antioxidant activity is closely related to phenolic content 40). The change in total phenolic content in legumes during germination is illustrated in Table 3. The phenolic concentration dramatically increased in all legumes after five days of germination. In ungerminated grains, the content of total phenolics ranged from 5.80 (mung beans) to 18.21 (peanuts) mg GAE/g dry sample. After 5 days of sprouting, the phenolic content in mung beans, white cowpeas, soybeans and peanuts increased 2-fold, while that in black beans and adzuki beans showed about a 50% and 25% increase, respectively. In particular, peanuts had the highest concentration, which was 37.59 mg GAE/g, followed by soybeans (28.27 mg GAE/g), white cowpeas (19.46 mg GAE/g), adzuki beans (16.96 mg GAE/g), black beans (16.47 mg GAE/g), and mung beans (14.97 mg GAE/g). Adzuki beans and black beans are dark skin seeds that contain anthocyanidin pigments consisting of delphinidin, cyanidin, pelargonidin, malvidin, and petunidin 41).

Table 3. Total phenolic content (mg GAE/g dry weight) of ungerminated and germinated legumes

Black BeansMung BeansPeanutsAdzuki BeansSoybeansWhite Cowpeas
0 h11.74 ± 0.075.80 ± 0.0518.21 ± 0.1512.21 ± 0.0612.12 ± 0.097.79 ± 0.02
24 h13.17 ± 0.10 r11.47 ± 0.09 tu26.89 ± 0.11 f13.64 ± 0.17 q21.46 ± 0.05 i11.33 ± 0.09 u
48 h13.62 ± 0.07 q12.32 ± 0.36 s28.71 ± 0.16 d15.59 ± 0.05 n21.61 ± 0.11 i14.06 ± 0.08 p
72 h14.20 ± 0.18 p12.28 ± 0.13 s29.39 ± 0.04 c15.89 ± 0.05 n23.92 ± 0.08 h14.71 ± 0.07 °
96 h13.47 ± 1.17 qr12.47 ± 0.09 s30.34 ± 0.09 b16.57 ± 0.05 m24.75 ± 0.15 g16.29 ± 0.11 m
120 h16.47 ± 0.14 m14.97 ± 0.09 °37.59 ± 0.18 a16.96 ± 0.06 l28.27 ± 0.11 e19.46 ± 0.09 j

Note: Means ± SD (standard deviation) that do not share a superscript letter are significantly different at 95% confidential level.

[Source 42)]

Table 4. Phenolic components and concentrations (µg/g dry weight) of legumes after 5-day germination

Phenolic componentsBlack BeansMung BeansPeanutsAdzuki BeansSoybeansWhite Cowpeas
Gallic acidndndndnd21.3 ± 2.9nd
Protocatechuic acidndnd15.1 ± 2.5 b2.2 ± 0.1 c41.5 ± 6.6 and
p-hydroxybenzoic acid24.1 ± 1.0 b15.9 ± 0.3 b16.8 ± 0.1 b19.5 ± 0.6 b66.6 ± 0.8 and
Vanillic acid43.8 ± 0.8 c5.2 ± 0.7e67.6 ± 0.8 b25.2 ± 0.9 d189.2 ± 10.1 and
Caffeic acidndndndndnd70.8 ± 6.6
Syringic acid79.8 ± 1.7 b16.7 ± 1.8 cnd23.8 ± 0.8 c327.5 ± 14.9 a30.4 ± 5.3 c
Vanillin12.4 ± 0.8 b14.2 ± 0.5 bnd15.9 ± 2.9 bnd28.9 ± 3.3 a
Ferulic acidnd26.6 ± 2.8 c330.3 ± 16.0 a15.7 ± 1.6 c72.9 ± 5.6 b18.2 ± 0.8 c
Sinapic acid109.1 ± 0.5 c163.5 ± 3.8 b247.9 ± 21.1 a150.7 ± 4.6 b218.1 ± 7.5 a99.65 ± 7.4 c
p-coumaric acid72.1 ± 3.1 b288.7 ± 3.6 and14.4 ± 2.8 c18.1 ± 4.5 c81.95 ± 0.65 b
Benzoic acid253.5 ± 26.7 b636.0 ± 2.4 and124.8 ± 51.9 cnd199.5 ± 36.4 bc
Ellagic acid54.4 ± 3.9 nsnd126.2 ± 89.3 ns30.3 ± 4.0 ns59.6 ± 2.4 ns48.3 ± 6.5 ns
Cinnamic acid14.85 ± 2.9 ab4.0±0.1 b62.9 ± 35.6 a3.1 ± 0.2 b36.2 ± 1.5 ab12.5 ± 3.2 ab

Note: Means ± SD (standard deviation) that do not share a letter in the same row are significantly different at 95% confidential level. ns: not significantly different; nd: not detected.

[Source 43)]

Table 5. Antioxidant activities of 5-day germinated legume extracts

SampleDPPH• Scavenging (%)Reducing Power (%)
Black beans7.44 ± 0.39 f64.92 ± 0.57 c
Mung beans17.46 ± 0.60 d26.45 ± 0.95 f
Peanuts32.51 ± 0.54 a84.48 ± 1.24 a
Adzuki beans20.80 ± 0.39 c42.51 ± 1.24 e
Soybeans26.94 ± 0.71 b75.08 ± 1.18 b
White cowpeas11.17 ± 0.63 e61.53 ± 0.68 d

Note: Means ± SD that do not share a superscript letter are significantly different at 95% confidential level.

The antioxidant activities of germinated legumes were evaluated by the DPPH method and the reducing power assay, as shown in Table 5. It was found that the six legume extracts had different antioxidant activity levels at a 0.1 mg/mL dose. In particular, peanuts had the highest antioxidant activity at 32.51%, which was significantly different from the others, while black beans showed the lowest antioxidant activity (7.44%). The reducing power of germinated peanuts obtained maximum activity (84.48%) compared to other studied legumes (Table 5), whereas the lowest antioxidant activity was mung beans (26.45%). Although adzuki beans had higher DPPH- scavenging activity than black beans and white cowpeas, the reducing power capacity of adzuki beans was, in contrast, significantly lower than that of black beans and white cowpeas (Table 5).

In this study, peanuts contained a maximum concentration of phenolics, which may result in the strongest antioxidant activity of the legume. Furthermore, according to Corral-Aguayo et al. 44), when compared to the antioxidant activity, resveratrol had stronger activity than flavonoids. In addition, the main substances in soybean phenolics were flavonoids, whereas, in other legumes (chickpeas and black, red, and white cowpeas), the major components were phenolic acids 45). This may explain why soybeans had greater antioxidant activities than the other four legumes in the DPPH assay.

[Source 46)]

Although no evidence is available for the mechanism of action of common beans on other kinds of cancer, the antiproliferative effect of legumes, including Adzuki beans, has been explored 47). Adzuki bean exhibited the strongest antiproliferative properties in a dose-dependent manner against all digestive system cancer cell lines (CAL27, AGS, HepG2, SW480 and Caco-2), ovary cancer cell SK-OV-3 and breast cancer cell MCF-7 among all legumes tested 48). Nakaya et al. 49) suggested that adzuki bean and its heat-stable extract is immunopotentiating foods that can be used as dietary supplements for cancer prevention and immunotherapy. Adzuki bean stimulates differentiation of bone marrow cells into immature dendritic cells with the greatest efficacy compared to 30 types of edible beans with biological activity. The level of IL-6 produced by sequential treatment of dendritic cells with Adzuki extract and lipopolysaccharide was the highest among the examined beans. Adzuki beans extract also inhibited the growth of human leukemia U937 cells, leading to induction of apoptosis. Further research is warranted regarding the implications and the molecular mechanisms in which adzuki beans and their bioactive compounds modulate the development of different types of cancer.

Hot-water adzuki beans extract contains such chemical compounds as catechins and saponins which are well-known bioactive ingredients 50). Ito and colleagues have previously reported that the 40% ethanol-eluted fraction of hot-water adzuki beans extract and HP-20 resin possessed antitumor 51), antioxidative 52) anti-metastatic 53) and anti-diabetic activities, 54), lowered the serum cholesterol levels 55) and enhanced melanogenesis 56). The color of hot-water adzuki beans extract originates from (+)-catechin 57). Choi et al. 58) and Nakamura et al. 59) have reported that (+)-catechin and green tea catechin regulated osteoblast and osteoclast differentiation.

Obesity increases the risk of metabolic disorders such as hyperglycemia, hyperlipidemia, hypercholesterolemia, and diabetes 60). Both an increased number of adipocytes (fat cells), due to enhanced differentiation of preadipocytes into adipocytes, and increased adipocyte size due to lipid accumulation are shown to participate in the expansion of adipose tissue 61). Numerous studies have suggested that oxidative stress may be the linking mechanism in the pathway leading from obesity to obesity-related chronic diseases 62). Black adzuki bean exhibited the greatest antioxidant activity compared to 20 other kinds of adzuki beans 63). Adzuki beans have been evaluated as potential remedies for hypercholesterolemia, hyperglycemia, and inflammation in mice and rats 64), 65) and preliminary data have shown that black adzuki beans inhibit proliferation and mitotic clonal expansion and subsequently inhibit the adipogenesis of 3T3-L1 cells 66). Although recent studies have reported evidence that the adzuki beans affect the regulation of lipid metabolism, it remains to be determined whether they may be effective in overcoming obesity by regulating appetite and satiety. Chau et al. 67) observed no changes in serum total cholesterol, LDL “bad” cholesterol and HDL “good” cholesterol levels in hamsters fed a hypercholesterolemic diet by using a adzuki bean protein concentrate.

In a study on mouse, a hot-water extract of adzuki beans was found to stimulate tyrosinase activity in cultured mouse B16 melanoma cells and hair color pigmentation in C3H mice 68). At concentrations of 1–3 mg/ml, adzuki beans hot-water extract stimulated melanogenesis without inhibiting cell growth. During this effect, WEx activated tyrosinase-inducing activity in the cells, but did not activate tyrosinase, which exists at an intracellular level. In this study, adzuki beans hot-water extract increased cyclic adenosine-3′,5′-monophospate (cAMP) content in the cells and protein kinase A (PKA) activity, and stimulated translocation of cytosolic protein kinase C to the membrane-bound protein kinase C 69). These results suggest that the addition of adzuki beans hot-water extract activates the adenylcyclase and protein kinase pathways and, as a result, stimulates melanogenesis. Adzuki beans hot-water extract was found to have pigmentation activity on hair color in C3H mice. This effect might be useful in anti-graying, protecting human skin from irradiation 70).

Azuki beans contain polyphenols such as proanthocyanidins that exhibit potential radical scavenging activities 71). Spontaneously hypertensive rats with approximately 200 mm Hg systolic blood pressure were randomly divided into 2 groups fed either 0% or 0.9% azuki bean extract-containing diet. Azuki bean extract reduced the elevated blood pressure and increased nitric oxide (NO) production in long-term treatment 72).

Osteoporosis is a global public health problem thought to be caused by an imbalance in bone metabolism. Bone metabolic balance (bone resorption and bone formation) is maintained by osteoclasts and osteoblasts 73). Aging is accompanied by disruption in bone metabolism leading to osteoporosis; the risk is particularly high in women who tend to lose bone after menopause. Aging-associated degeneration of the osteoblast function also reduces bone mass, as does malnutrition or under-nutrition (a deficiency of micronutrients and macronutrients). This study 74) the 40% ethanol fraction in combination with a hot-water adzuki beans extract was examined for its effect on osteoblast and osteoclast differentiation. Adzuki beans extract -treated mice preosteoblast MC3T3-E1 cells exhibited significantly elevated alkaline phosphatase activity and mineralization. Adzuki beans extract facilitated osteoblast differentiation by up-regulating such osteoblast differentiation-related molecules as runt-related transcription factor 2, distal-less homeobox 5, and osterix via p38 mitogen-activated protein kinase. In summary this study 75) suggest that 40% ethanol-eluted fraction of hot-water adzuki beans extract could be used to treat senile osteoporosis and postmenopausal osteoporosis. Lee et al. have reported that the consumption of such a legume as adzuki improved the levels of bone markers in ovariectomized rats 76). However what the active compound is in the hot-water adzuki beans extract have yet to be elucidated. Further studies are needed to verify the effect of 40% ethanol-eluted fraction of hot-water adzuki beans extract on osteoporosis in animal models.

References   [ + ]

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