The mung bean (Vigna radiata (L.) R. Wilczek) is a legume cultivated for its edible seeds and sprouts across Asia. There are 3 subgroups of Vigna radiata: one is cultivated (Vigna radiata subsp. radiata), and two are wild (Vigna radiata subsp. sublobata and Vigna radiata subsp. glabra). The mung bean plant is an annual, erect or semi-erect, reaching a height of 0.15-1.25 m (FAO, 2012; Lambrides et al., 2006; Mogotsi, 2006). It is slightly hairy with a well-developed root system. Wild types tend to be prostrate while cultivated types are more erect (Lambrides et al., 2006). The stems are many-branched, sometimes twining at the tips (Mogotsi, 2006). The leaves are alternate, trifoliolate with elliptical to ovate leaflets, 5-18 cm long x 3-15 cm broad. The flowers (4-30) are papillonaceous, pale yellow or greenish in colour. The pods are long, cylindrical, hairy and pending. They contain 7 to 20 small, ellipsoid or cube-shaped seeds. The seeds are variable in colour: they are usually green, but can also be yellow, olive, brown, purplish brown or black, mottled and/or ridged. Seed colours and presence or absence of a rough layer are used to distinguish different types of mung bean (Lambrides et al., 2006; Mogotsi, 2006). Cultivated types are generally green or golden and can be shiny or dull depending on the presence of a texture layer (Lambrides et al., 2006). Golden gram, which has yellow seeds, low seed yield and pods that shatter at maturity, is often grown for forage or green manure. Green gram has bright green seeds, is more prolific and ripens more uniformly, with a lower tendency for pods to shatter. In India, two other types of mung beans exist, one with black seeds and one with brown seeds (Mogotsi, 2006). The mung bean resembles the black gram (Vigna mungo (L.)) with two main differences: the corolla of Vigna mungo is bright yellow while that of Vigna radiata is pale yellow; mung bean pods are pendulous whereas they are erect in black gram. Mung bean is slightly less hairy than black gram. Mung bean is sown on lighter soils than black gram (Göhl, 1982).
The mung bean is a major edible legume seed in Asia (India, South East-Asia and East Asia) and is also eaten in Southern Europe and in the Southern USA. The mature seeds provide an invaluable source of digestible protein for humans in places where meat is lacking or where people are mostly vegetarian (AVRDC, 2012). Mung beans are cooked fresh or dry. They can be eaten whole or made into flour, soups, porridge, snacks, bread, noodles and ice-cream. Split seeds can be transformed into dhal in the same way as black gram or lentils. Mung beans can be processed to make starch noodles (vermicelli, bean thread noodles, cellophane noodles) or soap. The sprouted seeds ("bean sprouts" in English, and incorrectly called "germes de soja" or "pousses de soja" in French) are relished raw or cooked throughout the world. The immature pods and young leaves are eaten as a vegetable (Mogotsi, 2006).
Several mung bean products are useful for livestock feeding (Vaidya, 2001):
- Mung beans, raw or processed, as well as split or weathered seeds.
- By-products of mung bean processing: mung bean bran (called chuni in India), which is the by-product of dehulling for making dhal, and the by-product of the manufacture of mung bean vermicelli.
- Mung bean is sometimes grown for fodder as hay, straw or silage (Mogotsi, 2006). It is particularly valued as early forage as it outcompetes other summer growing legumes such as cowpea or velvet bean in their early stages (Lambrides et al., 2006).
The mung bean plant makes valuable green manure and can be used as a cover crop (Mogotsi, 2006).