*5.5.1 Vegetable soybean*

*Legume Crops - Prospects, Production and Uses*

medium-sized seeds are preferred for sprouts.

**5.4 Breeding targets for food grade soybeans**

**5.5 Large-seeded soybeans**

carries a flavor, called "beany flavor" or "grassy flavor." Genotypes with high levels of sucrose, aspartic acid, glutamic acid, and alanine are found to have acceptable taste [44]. Biochemical analysis has established that production of "beany flavor" in soybean or soy-based products is primarily due to the lipoxygenase or the oxidative rancidity of unsaturated fatty acids [45]. Plant lipids are sequentially degraded into volatile and nonvolatile compounds by a series of enzymes via the lipoxygenase pathway, which catalyzes the hydroperoxidation of polyunsaturated fatty acids to form the aldehyde and alcohols that are responsible for the grassy-beany flavor [46]. *Organic food-grade* soybeans are produced using cultivation practices that do not use synthetic compounds. In the U.S., growers producing and selling soybeans that are labeled "organic" must be certified by a USDA-approved state or private agency. The top selling organically produced soy products in the US are tofu and soymilk. Other specialty soybeans include varieties with low saturated fat, high isoflavone, high sucrose, high oleic acid, high stearate, or high protein. Large-seeded soybeans with thin seed coat and a clear hilum are preferred for the soynut market, while small- to

Breeding for food-grade soybeans with unique seed composition has focused on a specific nutritional trait of the soybean seed. Examples of such varieties are given according to the fraction from which the targeted trait origins. Food-grade soybean that targets a specific trait such as varieties high in total protein content, high in β-conglycinin, low in lipoxygenase, high in specific amino acids such as lysine, methionine, and threonine, and low in allergenic proteins [13]. High-protein soybeans (>43%) are used for tofu, soymilk, soy sauce, beverages, baked goods, pudding, cheese, and meat analogs. The breeding of food-grade soybeans can be classified into three major categories: the breeding of large-seeded soybeans, the breeding of smallseeded soybeans, and the breeding of soybean with unique seed composition [13].

By targeting specific traits, soybean breeders try to develop soybeans with good

yield and quality [5]. Large-seeded soybeans are bred for tofu, soymilk, miso, edamame, and soynuts [13]. An important factor for the breeding of tofu soybeans is the tofu yield, which is defined as the weight of fresh tofu produced from a unit of harvested soybean. Seed size and seed appearance are also of importance for tofu soybeans. Tofu soybeans are larger than 20 g/100-seeds [13]. It is possible to produce good quality tofu with dark hilum beans but this requires prior dehulling of the beans and careful soymilk filtration [5]. In order to avoid these additional processing steps, soybeans with a yellow cotyledon, yellow seed coat, and clear hilum are preferred. Moreover, a thin but strong seed coat that is free from cracking and discoloration is desirable [13]. Soybean seeds with high protein content exceeding 45% on dry matter basis and improved ratio of 11S/7S is desirable for tofu soybeans as this enhances tofu yield and gelling characteristics, respectively [5]. A high protein/oil ratio provides a higher tofu yield and firmer texture; therefore, low oil content is preferred. Moreover, tofu soybeans should have high water uptake, a low calcium content, and a high germination rate. The carbohydrate content and composition influence the taste of tofu and soymilk [13]. High total sugar content (above 8% on dry matter basis) [5], high sucrose, low raffinose, and low stachyose are highly desirable for tofu and soymilk [13]. Examples of tofu and soymilk varieties: Black Kato, Toyopro, Grande, Proto (from Minnesota), Vinton-81, HP 204,

IA1007, IA1008 (from Iowa), and Harovinton [13, 47].

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Vegetable soybean varieties should meet certain requirements such as sweeter seeds with thin seed coat and large seed size (>30 g/100-seeds dry weight) [13]. As the pods are eaten directly, genotypes with sparse gray pubescence with green and thin seed coat are preferred [13]. Moreover, edamame cultivars should possess as less as possible of one-seeded pods as they require greater effort to shell by consumers. Those cultivars with genetically "stay green" and delayed yellowing toward maturity make it possible for growers to have extended harvest period closer to maturity. Vegetable-type soybean should possess important nutritional traits such as high content of sugar (sucrose and maltose) and free amino acids to impart sweet and delicious taste. Sucrose is primarily responsible for the sweetness of vegetable soybeans, where sucrose content is preferably higher than 10% on dry matter basis. Certain free amino acids, such as glutamic acids, are major contributors to the taste of vegetable soybeans [13].
