The soybean, soy bean, or soya bean (Glycine max) is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses.
The soybean, soy bean, or soya bean (Glycine max) is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses.
Traditional unfermented food uses of soybeans include soy milk, from which tofu and tofu skin are made. Fermented soy foods include soy sauce, fermented bean paste, natto, and tempeh.
Fat-free (defatted) soybean meal is a significant and cheap source of protein for animal feeds and many packaged meals. For example, soybean products, such as textured vegetable protein (TVP), are ingredients in many meat and dairy substitutes.
Soybeans contain significant amounts of phytic acid, dietary minerals, and B vitamins. Soybean vegetable oil, used in food and industrial applications, is another product of processing the soybean crop. Soybean is the most important protein source for feeding farm animals, which in turn yield animal protein for human consumption.
Classification
The genus Glycine may be divided into two subgenera, Glycine and Soja. The subgenus Soja includes the cultivated soybean, G. max, and the wild soybean, treated either as a separate species, G. soja, or as the subspecies G. max subsp. soja. The cultivated and wild soybeans are annuals. The wild soybean is native to China, Japan, Korea, and Russia.
The subgenus Glycine consists of at least 25 wild perennial species, for example, G. canescents and G. tomatillo, both found in Australia and Papua New Guinea.
The perennial soybean, the edible bean, belongs to a different genus. It originated in Africa and is now a widespread pasture crop in the tropics. Like some other long-domesticated crops, the relationship of the modern soybean to wild-growing species can no longer be traced with any degree of certainty. It is a cultivar with a very large number of cultivars.
Germination
The first stage of growth is germination, a method that first becomes apparent as a seed radicle emerges. This is the first stage of root growth and occurs within the first 48 hours under ideal growing conditions.
The first photosynthetic structures, the cotyledons, develop from the hypocotyl, the first plant structure to emerge from the soil. These cotyledons both act as leaves and as a source of nutrients for the immature plant, providing the seedling nutrition for its first 7 to 10 days.
Maturation
The first true leaves develop as a pair of single blades. Subsequent to this first pair, mature nodes form compound leaves with three blades. Mature trifoliolate leaves, with three to four leaflets per leaf, are often between 6 and 15 cm (2+ 1 ⁄ 2 and 6 in) long and 2 and 7 cm (1 and 3 in) broad.
Under ideal conditions, stem growth continues, producing new nodes every four days. Before flowering, roots can grow up to 2 cm ( 3 ⁄ 4 in) per day. If rhizobia are present, root nodulation begins by the time the third node appears. Nodulation typically continues for 8 weeks before the symbiotic infection process stabilizes.
The final characteristics of an edible bean plant are variable, with factors such as genetics, soil quality, and climate affecting its form; however, fully mature soybean plants are generally between 50 and 125 cm (20 and 50 in) in height, with rooting depths between 75 and 150 cm (30 and 60 in).
Flowering
Flowering is triggered by day length, often beginning once days become shorter than 12.8 hours. This trait is highly variable, however, with different varieties reacting differently to changing day length Soybeans form inconspicuous, self-fertile flowers that are borne in the axil of the leaf and are white, pink, or purple.
Though they do not require pollination, they are attractive to bees because they produce nectar that is high in sugar content Depending on the soybean variety, node growth may cease once flowering begins. Strains that continue nodal development after flowering are termed indeterminates and are best suited to climates with longer growing seasons. Often, soybeans drop their leaves before the seeds are fully mature.
The fruit is a hairy pod that grows in clusters of three to five; each pod is 3–8 cm (1–3 in) long and usually contains two to four (rarely more) seeds that are 5–11 mm in diameter. Soybean seeds come in a wide variety of sizes and hull colors such as black, brown, yellow, and green. Variegated and bicolored seed coats are also common.
Seed resilience
The hull of the mature edible bean is hard, water-resistant, and it protects the cotyledon and hypocotyl (or germ) from damage. If the seed coat is cracked, the seed will not germinate. The scar, visible on the seed coat, is called the hilum (colors include black, brown, buff, gray, and yellow), and at one end of the hilum is the micropyle, or small opening in the seed coat which can allow the absorption of water for sprouting.
Some seeds, such as soybeans, which contain very high levels of protein, can undergo desiccation, yet survive and revive after water absorption. A. Carl Leopold began studying this capability at the Boyce Thompson Institute for Plant Research at Cornell University in the mid-1980s.
He found soybeans and corn to have a range of soluble carbohydrates that protected the seed viability. Patents were awarded to him in the early 1990s on techniques for protecting biological membranes and proteins in the dry state.
Nitrogen-Fixing Ability
Like many legumes, soybean, the edible bean, can fix atmospheric nitrogen due to the presence of symbiotic bacteria from the Rhizobia group. Together, protein and soybean oil content account for 56% of dry soybeans by weight (36% protein and 20% fat, table). The remainder consists of 30% carbohydrates, 9% water, and 5% ash (table). Soybeans comprise approximately 8% seed coat or hull, 90% cotyledons, and 2% hypocotyl axis or germ.
Nutrition
A 100-gram reference quantity of raw soybeans supplies 1,866 kilojoules (446 kilocalories) of food energy and is composed of 9% water, 30% carbohydrates, 20% total fat, and 36% protein (table).
Soybeans are a rich source of essential nutrients, providing in a 100-gram serving (raw, for reference) high contents of the Daily Value (DV), especially for protein (36% DV), dietary fiber (37% DV), iron (121%), manganese (120%), phosphorus (101%), and several B vitamins, including folate (94% DV) (table). High contents also exist for vitamin K, magnesium, zinc, and potassium.
For human consumption, soybeans must be cooked with heat to destroy the trypsin
inhibitors (serine protease inhibitors). Raw soybeans, including the immature green form, are toxic to all monogastric animals.
Protein
Most soy protein is a relatively heat-stable storage protein. This heat stability enables soy food products requiring high temperature cooking, such as tofu, soy milk and textured vegetable protein (soy flour) to be made. Soy protein is essentially identical to the protein of other legume seeds and pulses.
Soy is a good source of protein for vegetarians and vegans or for people who want to reduce the amount of meat they eat, according to the US Food and Drug Administration.
Although soybeans have high protein content, they also contain high levels of protease inhibitors, which can prevent digestion. Protease inhibitors are reduced by cooking soybeans and are present in low levels in soy products such as tofu and soy milk.
The Protein Digestibility Corrected Amino Acid Score (PDCAAS) of soy protein is the nutritional equivalent of meat, eggs, and casein for human growth and health. Soybean protein isolate has a biological value of 74, whole soybeans 96, soybean milk 91, and eggs 97.
All spermatophytes, except for the family of grasses and cereals, contain 7S (vicilin) and 11S (legumin) soy protein-like globulin storage proteins, or only one of these globulin proteins. S denotes Svedberg, sedimentation coefficients.
Oats and rice are anomalous in that they also contain most of the soybean-like protein. Cocoa, for example, contains the 7S globulin, which contributes to cocoa’s taste and aroma, whereas coffee beans (coffee grounds) contain the 11S globulin, responsible for coffee’s aroma and flavor.
