M A Grusak, Baylor College of Medicine, Houston, TX, USA
Legumes have been an important component of the human diet for several millennia and are used throughout the world today. They are a diverse group of plants that belong to the Fabaceae family (sometimes also referred to as the Leguminosae) and are estimated to include approximately 20,000 species in 700 genera. However, only a handful of these species have been developed as crops that are in common culture. Some of the more extensively grown legumes are listed in Table 1.
Legumes are consumed primarily as seed foods, but pods, leaves, and roots or tubers of various species are also eaten. The pod is an enveloping structure that protects the seeds as they develop and mature, and it is a characteristic feature of this group of plants. In fact, the name legume comes from the Latin word legumen, which means seeds that are harvested from pods. Other names used for legume seeds are pulse, which is derived from the Latin word puls, meaning pottage, or the phrase grain legume, used in reference to leguminous seeds. The more general phrase, food legume, is used to represent any vegetative or reproductive structures from legume plants that are utilized for human food.
An important nutritional aspect of legume foods is their high concentration of protein, which in most
Table 1 Commonly cultivated legume species
Arachis hypogea L. Cajanus cajan (L.) Millsp.
Cicer arietinum L.
Glycine max (L.) Merr. Lablab purpureus (L.) Sweet
Lathyrus sativus L. Lens culinaris Medik. Lupinus albus L. Macrotyloma uniflorum (Lam.)
Verdc. Phaseolus lunatus L. Phaseolus vulgaris L.
Pisum sativum L. Psophocarpus tetragonolobus
Marechal Vigna mungo (L.) Hopper Vigna radiata (L.) Wilczek
Vigna subterranea (L.) Verdc. Vigna umbellata (Thumb.)
Ohwi and Ohashi Vigna unguiculata (L.) Walp. ssp. unguiculata
Peanut, groundnut Pigeon pea, red gram,
Congo pea Chickpea, garbanzo,
Bengal gram Soybean, soya, edamame Hyacinth bean, Indian bean,
Egyptian bean Grass pea, chickling pea Lentil
Horse gram, Madras gram
Lima bean, butter bean Common bean, black bean, kidney bean, pinto bean, snap bean, string bean, French bean Pea, garden pea, English pea Winged bean, Goa bean, four-angled bean Broad bean, fava bean Moth bean, mat bean
Urd bean, black gram Mung bean, green gram, golden gram Bambara groundnut Rice bean, Mambi bean
Cowpea, black-eyed pea, southern pea
Source: Rubatzky VE and Yamaguchi M (1997) World Vegetables: Principles, Production, and Nutritive Values. New York: Chapman & Hall.
legume seeds is at least twice that of cereal seeds. Legumes can produce more protein because the plants are generally well nourished with nitrogen, even in soils with limited inorganic nitrogen. Legume roots have the ability to form symbiotic associations with particular microbial species, in a structure called the root nodule. This symbiosis allows the plant to readily acquire atmospheric nitrogen and use it for the synthesis of amino acids. These protein precursors are transported to the developing seeds and are deposited there for later use. Legume seeds also contain a broad mix of energy reserves (starch or oil), minerals, and various phytochemicals—all of which are stored in seeds to provide nourishment to the young developing seedling.
As omnivores, humans have been able to take advantage of the nutrient and phytochemical reserves in legume seeds for dietary requirements and health benefits. This is especially important in the developing world, where malnutrition is an ever-present concern, and legumes can provide an inexpensive source of dietary protein (relative to animal food products), among other nutrients. The protein in legume seeds, although somewhat lacking in sulfur amino acids and tryptophan, is still an important complement to energy-rich carbohydrate staples, such as rice, wheat, maize, and various root and tuber crops. However, when eating legumes, we also must deal with the various antinutrients and toxic compounds found in seeds. These seed components include various enzyme inhibitors, tannins, phenolics, alkaloids, and neurotoxins. Some of these can cause debilitating consequences in humans, although cooking and other processing techniques can be used to reduce or alleviate their negative effects.
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