What are mung beans

Mung bean (Vigna radiata) are also known as the moong bean, green gram, or mung, is a plant species in the legume family. The mung bean is mainly cultivated in Pakistan, India, China, Korea, and Southeast Asia. Mung bean is commonly used as an ingredient in both savory and sweet dishes across Asia.

Skin color of mung bean can be classified into dark green or green black. The best grade mung beans is the one lustrous, big size round shape and easy broken when boiled.

The mung bean has been consumed as a common food in China for more than 2,000 years. It is well known for its detoxification activities and is used to refresh mentality, alleviate heat stroke, and reduce swelling in the summer. In the book Ben Cao Qiu Zhen, the mung bean was recorded to be beneficial in the regulation of gastrointestinal upset and to moisturize the skin ¹⁾. The seeds and sprouts of mung beans are also widely used as a fresh salad vegetable or common food in India, Bangladesh, South East Asia, and western countries ²⁾. As a food, mung beans contain balanced nutrients, including protein and dietary fiber, and significant amounts of bioactive phytochemicals. High levels of proteins, amino acids, oligosaccharides, and polyphenols in mung beans are thought to be the main contributors to the antioxidant, antimicrobial, anti-inflammatory, and antitumor activities of this food and are involved in the regulation of lipid metabolism ³⁾.

In recent years, studies have shown that the sprouts of mung beans after germination have more obvious biological activities and more plentiful secondary metabolites since relevant biosynthetic enzymes are activated during the initial stages of germination. Thus, germination is thought to improve the nutritional and medicinal qualities of mung beans ⁴⁾. Highly efficient use of mung beans according to evidence demonstrated from scientific experiments will be beneficial to the application of mung beans as a health food, medicine, and cosmetic ⁵⁾.

During the germination process of the mung bean, its chemical constituents undergo a series of biochemical reactions. One such reaction is the synthesis of small active compounds from macromolecular substances, promoting absorption and utilization. Another change observed during germination is the formation and accumulation of many types of active substances, such as polyphenols, saponins, vitamin C, etc. Therefore, we believes that these changes in the chemical composition of mung beans during germination will lead to substantial and important changes in the pharmacological activities of mung beans as well.

Mung beans nutrition

Mung beans are composed of about 20%–24% protein. Globulin and albumin are the main storage proteins found in mung bean seeds and make up over 60% and 25% of the total mung bean protein, respectively. Therefore, due to its high protein content and digestibility, consumption of mung beans in combination with cereals can significantly increase the quality of protein in a meal ⁶⁾. Mung bean protein is rich in essential amino acids, such as total aromatic amino acids, leucine, isoleucine, and valine, as compared with the FAO/WHO (1973) reference. However, compared with the reference pattern, mung bean protein is slightly deficient in threonine, total sulfur amino acids, lysine, and tryptophan ⁷⁾. Moreover, the proteolytic cleavage of proteins during sprouting leads to a significant increase in the levels of amino acids.

Mung beans have much greater carbohydrate content (50%–60%) than soybeans, and starch is the predominant carbohydrate in the legume. Due to its high starch content, mung beans have typically been used for the production of starchy noodles, also called muk in Korea. Oligosaccharides, including raffinose, stachyose, and verbascose, in raw or poorly processed legumes are associated with flatulence in the human diet. While these oligosaccharides are present in mung beans, they are soluble in water and can be eliminated by adequate presoaking, germination, or fermentation. The energy offered by mung beans and sprouts is lower than that of other cereals, which is beneficial for individuals with obesity and diabetes ⁸⁾. In addition, trypsin inhibitors, hemagglutinin, tannins, and phytic acid found in the mung bean have also been reported to have biological functions, promoting digestion and eliminating toxins ⁹⁾.

In addition to high protein and low energy content, mung beans also contain various enzymes and plentiful microelements. For example, superoxide dismutase (SOD) extracted from the mung bean can be chemically modified and made into an SOD oral liquid. This chemically modified SOD can avoid destruction by gastric acid and pepsin, thereby extending its half-life, making it suitable for human oral absorption ¹⁰⁾.

Overall, regular consumption of mung beans could regulate the flora of enterobacteria, decrease the absorption of toxic substances, reduce the risk of hypercholesterolemia and coronary heart disease, and prevent cancer ¹¹⁾.

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

[Source ¹²⁾]

Table 2. Mung beans (raw) sprouted nutrition facts

[Source ¹³⁾]

Table 3. Mung beans sprouted, cooked, boiled, drained, without salt nutrition facts

[Source ¹⁴⁾]

How to sprout mung beans

Mung beans are sprouted (germinated) by leaving them in water for four hours of daytime light and spending the rest of the day in the dark. Mung bean sprouts can be grown under artificial light for four hours over the period of a week. They are usually simply called “bean sprouts”. However, when bean sprouts are called for in recipes, it generally refers to mung bean sprouts.

How to cook mung beans

Mung bean sprouts are stir-fried as a Chinese vegetable accompaniment to a meal, usually with garlic, ginger, spring onions, or pieces of salted dried fish to add flavour. Uncooked bean sprouts are used in filling for Vietnamese spring rolls, as well as a garnish for phở. They are a major ingredient in a variety of Malaysian and Peranakan cuisine, including char kway teow, hokkien mee, mee rebus, and pasembor. In Korea, slightly cooked mung bean sprouts, called sukjunamul, are often served as a side dish. They are blanched (placed into boiling water for less than a minute), immediately cooled in cold water, and mixed with sesame oil, garlic, salt, and often other ingredients. In the Philippines, mung bean sprouts are made into lumpia rolls called lumpiang togue. In Indonesia the food are often used as fillings like Tahu Isi (stuffed tofu) and complementary ingredient in many dishes such as rawon and soto.

In northern China and Korea, soybean sprouts, called kongnamul in Korean, are more widely used in a variety of dishes. The “blue sprouts” are toxic since they contain small quantities of hydrogen cyanide, like potato sprouts do.

Whole mung beans and paste

Whole cooked mung beans are generally prepared from dried beans by boiling until they are soft. Mung beans are light yellow in colour when their skins are removed. Mung bean paste can be made by dehulling, cooking, and pulverizing the beans to a dry paste ¹⁵⁾.

Although whole mung beans are also occasionally used in Indian cuisine, beans without skins are more commonly used; but in Kerala and Tamil Nadu, whole mung beans (mung beans are called as pachai payaru) are commonly boiled to make a dry preparation often served with rice gruel (kanji). Dehulled mung beans can also be used in a similar fashion as whole beans for the purpose of making sweet soups. Mung beans in some regional cuisines of India are stripped of their outer coats to make mung dal. In the South Indian States of Karnataka, Tamil Nadu, Telangana and Andhra Pradesh, steamed whole beans are seasoned with spices and fresh grated coconut in a preparation called Usli in Kannada or Sundal in Tamil. In south and north Indian states, mung beans are also eaten as pancakes. They are soaked in water for six to 12 hours (the higher the temperature, the lesser soaking time). Then they are ground into fine paste along with ginger and salt. Then pancakes are made on a very hot griddle. These are usually eaten for breakfast. This provides high quality protein that is rare in most Indian regional cuisines. Pongal or kichdi is another recipe that is made with rice and mung beans without skin. In Kerala, it is commonly used to make the parippu preparation in the Travancore region (unlike Cochin and Malabar, where toor dal, tuvara parippu is used). It is also used, with coconut milk and jaggery, to make a type of payasam. Soaked Moong (both full or split) called Hesaru in Kannada is one of ingredient in Kosambari a salad.

In Chinese cuisine, whole mung beans are used to make a tángshuǐ, or dessert, otherwise literally translated, “sugar water”, called lǜdòu tángshuǐ, which is served either warm or chilled. In Indonesia, they are made into a popular dessert snack called es kacang hijau, which has the consistency of a porridge. The beans are cooked with sugar, coconut milk, and a little ginger.

In Hong Kong, dehulled mung beans and mung bean paste are made into ice cream or frozen ice pops. Mung bean paste is used as a common filling for Chinese mooncakes in East China and Taiwan. Also in China, the boiled and shelled beans are used as filling in glutinous rice dumplings eaten during the dragon boat festival. The beans may also be cooked until soft, blended into a liquid, sweetened, and served as a beverage, popular in many parts of China.

In Korea, skinned mung beans are soaked and ground with some water to make a thick batter. This is used as a basis for the Korean pancakes called Bindae-tteok.

In the Philippines, ginisáng monggó (sautéed mung bean stew), also known as monggó guisado or balatong, is a savoury stew of whole mung beans with prawns or fish. It is traditionally served on Fridays of Lent, when the majority Roman Catholic Filipinos traditionally abstain from meat.[citation needed] Variants of ginisáng monggó may also be made with chicken or pork.

Mung bean paste is also a common filling of pastries known as hopia (or bakpia) popular in Indonesia, the Philippines and further afield in Guyana (where it is known as black eye cake) and originating from southern China.

Mung bean starch, which is extracted from ground mung beans, is used to make transparent cellophane noodles (also known as bean thread noodles, bean threads, glass noodles, fensi, tung hoon, miến, bún tàu, or bún tào). Cellophane noodles become soft and slippery when they are soaked in hot water. A variation of cellophane noodles, called mung bean sheets or green bean sheets, are also available. In Korea, a jelly called nokdumuk (also called cheongpomuk) is made from mung bean starch; a similar jelly, colored yellow with the addition of gardenia coloring, is called hwangpomuk. In northern China, mung bean jelly is called liangfen (meaning chilled bean jelly), which is a very popular food during summer. Jidou liangfen is another flavor of mung bean jelly food in Yunnan, in southern China.

Mung batter is used to make crepes named pesarattu in Andhra Pradesh, India and pancakes named Bindaetteok in Korea.

Mung beans health benefits

During the past few decades, flavonoids, phenolic acids, organic acids and lipids have been identified from the seeds and sprouts of mung beans and have been shown to contribute to its pharmaceutical activities. The structures of these constituents and corresponding plant sources are summarized in Figure 1.

Figure 1. Structures of chemical components of mung bean seeds and sprouts

Flavonoids

Flavone, isoflavone, flavonoids, and isoflavonoids (compounds 1–44 in Table 4) are the important metabolites found in the mung bean ¹⁶⁾. Most flavonoids have polyhydroxy substitutions and can be classified as polyphenols with obvious antioxidant activity. Vitexin (apigenin-8-C-β-glucopyranoside) and isovitexin (apigenin-6-C-β-glucopyranoside) have been reported to be present in mung bean seeds at about 51.1 and 51.7 mg g−1, respectively ¹⁷⁾. Flavonoids are involved in stress protection (i.e., oxidative and temperature stress), early plant development, signaling (i.e., legume nodulation), and protection from insect and mammalian herbivores ¹⁸⁾.

Phenolic acids

Phenolic acids are secondary metabolites primarily synthesized through the pentose phosphate pathway (PPP) and shikimate and phenylpropanoid pathways ¹⁹⁾. Phenolic acids are major bioactive phytochemicals, and their presence in wild plants has facilitated the trend toward the increasing use of wild plants as foods ²⁰⁾.

Twelve phenolic acids (compounds 45–56 in Table 4) have been identified from mung bean seeds and sprouts ²¹⁾. Based on high levels of total phenolics and total flavonoids, mung beans show the benefits of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities, tyrosinase inhibition, and antiproliferative and alcohol dehydrogenase activities, which allow it to be used as a substitution for proper prescription drugs and as a preventative or therapeutic agent for the treatment of human diseases ²²⁾.

Others

Organic acids and lipids have also been found in mung beans and sprouts. Twenty-one organic acids, including phosphoric and citric acid, and 16 lipids, including γ-tocopherol, were reported to be the major components of mung beans by gas chromatography/mass spectrometry (GC/MS) ²³⁾.

Table 4. Chemical constituents identified from mung bean seeds and sprouts

Biological activities

In ancient books, mung beans were well known for their detoxification activities. Mung bean protein, tannin, and other polyphenols are thought to combine with organophosphorus pesticides, mercury, arsenic, and other heavy metals, promoting the excretion of sediments from the body ²⁴⁾. Mung beans have been shown to possess antioxidant, antimicrobial, and anti-inflammatory activities. Moreover, mung beans have antidiabetic, antihypertensive, lipid metabolism accommodation, antihypertensive, and antitumor effects, among others (Table 5). These various properties of mung beans are discussed below.

Table 5. Biological activities and compounds of mung beans

Antioxidant effects

The proteins, polypeptides, polysaccharides, and polyphenols from the seeds, sprouts, and hulls of mung beans all show potential antioxidant activity. The antioxidant capacities of mung bean protein hydrolysate (MPH) have been reported as 0.67 and 0.46 μmol Trolox equivalent (TE)/mg protein, as measured by oxygen radical absorbance capacity-fluorescein (ORACFL) and Trolox equivalent antioxidant capacity (TEAC) assays, respectively. Freeze-drying in lactose excipient reduces the antioxidant capacity of MPH to 0.48 μmol TE/mg protein in the ORACFL assay, but does not alter the results of the TEAC assay ²⁵⁾.

MP1 and MP2, isolated from the water extract of mung beans, are 2 acid heteropolysaccharides with 9.9% and 36.4% uronic acid content, respectively. The main composition of MP1 (molecular weight: 83 kDa) is mannose, whereas MP2 (molecular weight: 45 kDa) consists of rhamnose and galactose. MP2 exhibits higher hydroxyl radical-scavenging activity, while MP1 has higher reducing power and stronger scavenging capacity for superoxide and DPPH radicals, as well as greater inhibition of the self-oxidation of 1,2,3-phentriol than MP2 ²⁶⁾.

Importantly, mung bean extracts possess significantly higher radical scavenging activities, greater reducing power, and higher levels of polyphenols than soy bean extracts, suggesting that they are superior functional foods. Indeed, the radical scavenging activities of DPPH and 2,2′-azino-di-(3-ethyl-2,3-dihydrobenzthiazoline −6-sulfonate) (ABTS) isolated from mung bean extracts were found to be 11.33 ± 0.24 and 36.65 ± 0.63 μmol/g, respectively, and the ferric reducing antioxidant power (FRAP) of mung bean extracts was 31.85 ± 3.03 μmol/g. Mung bean extracts reduce the rate of pyrogallol autoxidation by 85% compared to the control and possess SOD-like activity of 83.48% ± 0.88% ²⁷⁾.

During the sprouting process, sprout extracts show higher amounts of total phenolics, total flavonoids, and DPPH radical scavenging activity than seed extracts ²⁸⁾. Additionally, the antioxidant activity of mung bean sprouts is the highest on day 1 or 2, depending on the analysis method used (i.e., β-carotene assay or DPPH assay, respectively) ²⁹⁾.

The DPPH scavenging activity (SA) of mung bean soup (MBS; 20 mg/mL) is approximately 145% that of tea soup (5 mg/mL) and 195% that of vitamin C solution (0.15 mg/mL), indicating that the DPPH-SA of 100 g mung bean is equivalent to that of 36.3 g dried green tea and 1462 mg vitamin C. Vitexin and isovitexin are the major antioxidant components in mung beans ³⁰⁾. Vitexin inhibits DPPH radicals by approximately 60% at 100 μg/mL and effectively prevents UV-induced skin cell death ³¹⁾.

Antimicrobial activity

The use of phytochemicals as natural antimicrobial agents, commonly called ‘biocides’ is gaining popularity. Enzymes, peptides, and polyphenols extracted from mung beans have been shown to possess both antimicrobial and antifungal activities. Assays for antifungal activity are usually executed using the method of inhibition crescents, while assays for antimicrobial activity are performed using the deferred plate method or the agar-diffusion method ³²⁾.

A nonspecific lipid transfer peptide (nsLTP; molecular weight: 9.03 kDa) with antimicrobial and antifungal activity was isolated from mung bean seeds. Interestingly, nsLTP exerts antifungal effects on Fusarium solani, F. oxysporum, Pythium aphanidermatum, and Sclerotium rolfsii and antibacterial effects on Staphylococcus aureus but not Salmonella typhimurium ³³⁾.

Mungin, a novel cyclophilin-like antifungal protein isolated from mung bean seeds, possesses activity against the fungi Rhizoctonia solani, Coprinus comatus, Mycosphaerella arachidicola, Botrytis cinerea, and F. oxysporum. Mungin also exerts inhibitory activity against α- and β-glucosidases, suppressing [3H] thymidine in corporation by mouse splenocytes ³⁴⁾.

In 2005, a chitinase (30.8 kDa) with antifungal activity was isolated from mung bean seeds. The protein has a pI of 6.3, as determined by isoelectric focusing, and an estimated specific activity of 3.81 U/mg. The enzyme exhibits optimal activity at pH 5.4 and is stable from 40 to 50°C. Importantly, chitinase exerts antifungal activity on R. solani, F. oxysporum, M. arachidicola, P. aphanidermatum, and S. rolfsii ³⁵⁾.

In addition to the above antimicrobial and antifungal effects, polyphenol extracts from mung bean sprouts have also been shown to have activity against Helicobacter pylori, one of the most common bacterial infections in human beings causing gastroduodenal disease ³⁶⁾.

Anti-inflammatory activity

In Asia, mung beans have been used in various cuisines and in folk remedies to treat toxic poisoning, heat stroke associated with thirst, irritability, and fever; these beneficial effects of mung beans are thought to be related to the inflammatory response ³⁷⁾.

Researchers have analyzed the anti-inflammatory effects of mung bean ethanol extracts on lipopolysaccharide (LPS)-stimulated macrophages. The extract mainly included polyphenols, gallic acid, vitexin, and isovitexin and markedly reduced the activity of murine macrophages through the prevention of pro-inflammatory gene expression without cytotoxicity ³⁸⁾. Moreover, a study demonstrated that all pro-inflammatory cytokines, including interleukin (IL)-1β, IL-6, IL-12β, tumor necrosis factor (TNF)-α, and inducible NO synthase (iNOS), were dramatically down regulated in cells treated with 3.7 mg/mL polyphenols. These results suggested that the ethanol extract had great potential to improve the clinical symptoms of inflammation-associated diseases, such as allergies and diabetes ³⁹⁾.

The immune modulatory activities of mung bean water extracts and monomers on human peripheral blood mononuclear cells (PBMCs) have also been evaluated by BrdU immunoassay, secretion of interferon-gamma (IFN-γ) and IL-10, and elucidation of the responding cells by flow cytometry. The results demonstrated that 20 μg/mL genistein, phytic acid, and syringic acid induce a Th1-predominant immune response through significant suppression of IL-10 secretion and promotion of IFN-γ secretion. The study concluded that several non-nutritional ingredients of mung beans, such as flavonoids, acids, and plant hormones, are most likely to be important in the modulation of human immunity ⁴⁰⁾.

Antidiabetic effects

Studies have also investigated the antidiabetic effects of mung bean extracts. In a study conducted in 2008, the antidiabetic effects of mung bean sprout extracts and mung bean seed coat extracts were investigated in type 2 diabetic mice (male KK-Ay mice and C57BL/6 mice). These extracts were orally administered to KK-Ay mice for 5 weeks, and mung bean sprout extracts (2 g/kg) and mung bean seed coat extracts (3 g/kg) lowered blood glucose, plasma C-peptide, glucagon, total cholesterol, triglycerides, and blood urea nitrogen (BUN) levels. At the same time, both treatments markedly improved glucose tolerance and increased insulin immunoreactive levels ⁴¹⁾.

Phenolic antioxidants and levo-dihydroxy phenylalanine (L-DOPA) can be enriched in mung bean extracts through solid-state bioconversion (SSB) by R. oligosporus, with the goal of enhancing health-linked functionality. α-Amylase is responsible for cleaving starch during the digestive process, which is important in the management of postprandial blood glucose levels. A study in 2007 by Randir and Shetty investigated the inhibition of α-amylase and H. pylori in bioprocessed extracts and linked these effects to diabetes management and peptic ulcer management, respectively. The α-amylase inhibition potential of the tested sprouts extract was moderately high during early stages (days 0–2) and was higher during days 4–10, which correlated with higher phenolic content ⁴²⁾.

Lipid metabolism accommodation

The modulation of lipid metabolism by mung bean has been well established. In an early study, rabbits with hyperlipidemia were fed a 70% mixture of mung bean meal and mung bean sprout powder. The mixtures affected the total cholesterol and β-lipoprotein content, alleviating symptoms of coronary artery diseases ⁴³⁾. Additionally, in more recent studies, normal mice and rats were fed mung bean extracts for 7 days, and total cholesterol was significantly decreased in both types of rodents. This effect was thought to arise from the phytosterol content of mung beans, which was similar to blood cholesterol, facilitating the prevention of cholesterol biosynthesis and absorption ⁴⁴⁾.

Antihypertensive effects

High doses (600 mg peptide/kg body weight) of raw sprout extracts, dried sprout extracts, and enzyme-digested sprout extracts have been shown to significantly reduce systolic blood pressure (SBP) in rats after administration for 6–9, 3–6, or 3–9 h, respectively. Similar changes were found in the plasma angiotensin I-converting enzyme (ACE) activity of these mung bean extracts. A long-term (1-month) intervention study that included treatment with fresh sprout powder, dried sprout powder, and concentrated extracts of the sprouts was carried out. The results indicated that the sprout powders were not as efficacious as concentrated sprout extracts. The SBPs of rats treated with concentrated extracts of fresh and dried sprouts were significantly reduced during the intervention period from weeks 1–4 and weeks 2–4, respectively ⁴⁵⁾.

Antitumor effects

Mung beans have been shown to exert antitumor effects through several different mechanisms. The recombinant plant nucleases R-TBN1 and R-HBN1, similar to nucleases derived from pine pollen and mung beans, were found to be effective against melanoma tumors and were about 10-times more potent than bovine seminal ribonuclease (RNase). Due to their relatively low cytotoxicity and high efficiency, these recombinant plant nucleases appear to be stable biochemical agents that can be targeted as potential antitumor cytostatics ⁴⁶⁾.

In addition, mung beans have been shown to exert antiproliferative effects, as examined by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay using an in vitro cell culture system. Mung beans exhibit dose-dependent antiproliferative effects against the tongue squamous cell carcinoma cell line CAL27 and several other cancer cell lines tested (i.e., DU145, SK-OV-3, MCF-7, and HL-60 cells) ⁴⁷⁾.

Another study evaluated the effects of trypsin inhibitors from mung beans (i.e., LysGP33) on the metastasis and proliferation of human colon cancer cells (SW480 cells). In this study, the effects of the purified GST-LysGP33 active fragment on the migration of SW480 cells were detected using wound healing assays. The results showed that 10 μmol/L GST-LysGP33 active fragment affected cell migration beginning at the 24-h time point. After 72 h, cells treated with GST-LysGP33 exhibited an approximate 50% reduction in wound healing compared to the control group ⁴⁸⁾.

Antisepsis effects

The aqueous extract from mung bean coat (MBC) is protective against sepsis in vitro and in vivo. The effect was achieved by the inhibition of high mobility group box 1 (HMGB1), a nucleosomal protein that has recently been established as a late mediator of lethal systemic inflammation with a relatively wider therapeutic window for pharmacological interventions. It was found that MBC dose-dependently attenuated the LPS-induced release of HMGB1 and several chemokines in macrophage cultures. The animal survival rates after oral administration of MBC were significantly increased from 29.4% (in the saline group, N = 17 mice) to 70% (in the experimental MBC extract group, N = 17 mice, P < 0.05) ⁴⁹⁾. Chlorogenic acid has also been shown to be protective against lethal sepsis by inhibiting late mediators of sepsis. Chlorogenic acid suppresses endotoxin-induced HMGB1 release in a concentration-dependent manner in murine peritoneal macrophages. Additionally, administrations of chlorogenic acid attenuate systemic HMGB1 accumulation in vivo and prevented mortality induced by endotoxemia and polymicrobial sepsis ⁵⁰⁾.