**1. Introduction**

Soybean [*Glycine max* (L.) Merr.] is one of the most important crops in the world. Soybean seeds are distinguished from other legume grains especially by their high protein content. It is a major source of vegetable protein and oil in human food industries because of its nutritive and health benefits [1]. Owing to its health benefits, soy food has been part of the Asian diet for several centuries [2]. Soyfood has nutritional qualities that reduce human blood serum cholesterol levels and lower the risk of cardiovascular diseases [3]. Soy food is a natural source of isoflavones (daidzein, genistein, and glycitein) and a good source of calcium [4].

Soybeans typically possess protein and oil contents of approximately 40 and 20%, respectively. This composition gives the possibility for a broad variety of applications such as feed, biodiesel, edible oils, and other food products. Commercially, soybean can be categorized as (i) commodity type, mainly used for oil and animal feed, and (ii) food type soybean, mainly used for human consumption. One important application of soybean is its use in animal feed. Approximately 85%

of the soybean is crushed into oil and meal. The greatest part of the meal is used as protein source in animal feed, Approximately 6% of the produced soybean is directly used for food purposes [5]. When soybean is exclusively used for consumption by the farm animals, nutritionally, it should have at least 36% protein to meet part of their daily requirement for protein. The food-type soybean, on the other hand, contains protein higher than feed-grade soybean; it usually ranges between 40 and 45%. It helps in making better quality soy-based food products. Usually, food-grade soybeans are used for production of soy milk, tofu or soy paneer, soy sprouts, and other soy-based food items.

Globally soybean meal accounts for 63% of all the protein sources in animal feed. Next to the soybean meal, soybean oil obtained after crushing is refined and used as cooking oils and salad oils, and they can also find their use in mayonnaise and butter substitute. Soybean oil is refined and lecithin is obtained as a main by-product. Lecithins are found in many products such as in chocolate, margarine, and emulsifying agents [6]. Furthermore, the unraveling of the health and nutritional benefits of soybean contributed to increased interest for soybeans destined for food production, the so-called food-grade soybeans. Hence, the breeding of cultivars with enhanced food-grade traits is gaining great importance [7]. Soy foods available in the market can be divided in traditional and non-traditional soy foods. Traditional soy foods includes edamame (green vegetable soybeans), soy milk (a drink produced by soaking and grinding soybeans, boiling the mixture, and filtering out remaining particulates), tofu (soybean curd), tempeh (made of whole cooked soybeans), miso (fermented soup-based paste), soy sauce, okara, natto (fermented whole soybeans), and soy sprouts. They originated from Asia where soybean has been grown for centuries before its introduction to the rest of the world. Non-traditional foods are, for instance, soy yoghurt, soy cheese, pudding, snacks, etc. [6]. Soy food available in the market is classified into two groups based on the soybean seed size. Soy foods made of large seeds (>20 g/100 seeds) include tofu, edamame, miso, and soy milk. Soy foods made of small seeds (<12 g/100 seeds) include natto, soy sauce, tempeh, and bean sprouts.

Soybean seed needs to satisfy specific physical and chemical requirements for soy food production. In addition to seed size, visual appearance such as uniformity of seed size and shape with light-colored hilum and yellow seed coat without physical damage such as mottling, splits, shriveling, purple stain, and insect damage are the main consideration of food-grade soybeans [8]. It is reported that the seed size uniformity affected water absorption and the quality of the final soy product [9]. Shrunken or discolored seeds were undesirable due to the consumer requirements [10]. Stone seeds that do not absorb water during soaking cause serious problems for food processing as it affects the texture and consistency of the soy products particularly for fermented soy food such as natto [11]. Seeds with harder texture have higher calcium content and absorb less water [12]. Seed's hardness could be estimated by the seed swell ratio that was related to seed weight or water volume change before and after soaking [13]. High water absorption was required to obtain soft steamed seeds [14]. Thus, soybean seeds with rapid and high water uptake are preferred by processors in order to provide more products per unit of time [9]. However, seed composition requirements vary according to the type of soy food. Soybean seeds with high protein content (>45%), low oil content, high sucrose content, and low oligosaccharides (raffinose and stachyose) content are suitable for making tofu. For soy food such as natto made through short fermentation process, soybean seed with a high carbohydrate content are preferred for the purpose of getting a quick conversion to simple sugars [10].

**53**

*Food Grade Soybean Breeding, Current Status and Future Directions*

Like other plants, soybean too synthesizes a range of secondary metabolites for their adaptation and self-protection, called anti-nutritional factor (ANF). From nutritional point of view, the ANF is considered as harmful and toxic, as it interferes with normal growth, reproduction, and health. Therefore, soybean, in general, and food-grade soybeans, in particular, are expected to be free from anti-nutritional factors or allergens that may cause harm to the consumers. Soybean contains several anti-nutritional factors among which trypsin inhibitor (TI) and phytase are the most important ones. Kunitz trypsin inhibitor (KTI), which constitutes more than 80% of the total TI, is primarily responsible for improper digestibility of soybean, if consumed unprocessed. Although KTI is heat labile, yet heat inactivation process is neither fully effective nor economic. Genetic elimination of KTI is the most effective way of making soybean free

Soybean seeds contain phosphorus in the form of inositol hexaphosphate commonly known as phytate [16]. Besides sequestering inorganic phosphate, phytate may also chelate divalent cations such as Fe, thereby decreasing their availability. It also contributes toward water pollution by eutrophication as the phosphate-rich waste discharges into water bodies. So, reduction of seed phytase can enhance mineral and protein bioavailability in soybean. Microarray-based gene expression profiling of phytic acid biosynthesis pathway indicated stepwise regulation of eight genes, viz. myo-inositol-3-phosphatesynthaes (MIPS), inositol phosphate kinase (IPK1–4), etc. Gene silencing constructs were used to silence *GmIKP1* and *GmIPK2* through seedspecific vicilin/conglycinin promoters [17]. Similarly, mutation breeding through gamma irradiation has also been attempted to develop plants with reduced or zero

Vast areas of agricultural soils are contaminated with Cadmium (Cd) through the use of super phosphate fertilizers, sewage sludge, and inputs from the mining and smelting industries [18]. Cadmium (Cd) is a highly toxic element for human beings because of its extremely long biological half-life. Soybeans grown in cadmium-contaminated soil take up cadmium by roots and translocate into aerial organs, where it affects photosynthesis and consequently root and shoot growth. Many soybean cultivars can accumulate high Cd concentration in seed when grown on Cd-polluted soil [19, 20]. Consumption of food containing excessive Cd leads to a risk of chronic toxicity. In humans, it can damage kidneys, causing a loss of calcium and associated osteoporosis [21]. To reduce the health risk, it is desirable to limit the concentration of Cd in crops used for human consumption. Due to growing concern about safety of foods and human health, the Codex Alimentarius Commission of Food and Agriculture Organization/World Health

Organization (FAO/WHO) has proposed an upper limit of 0.2 mg kg<sup>−</sup><sup>1</sup>

the international allowable limit of 0.2 mg kg<sup>−</sup><sup>1</sup>

concentration in soybean grain [22]. However, a large-scale survey of agricultural products revealed that the Cd concentration of 16.7% of soybean seeds exceeded

of other upland crops [23]. Cultivars with reduced uptake of Cd are needed for

for Cd

, which is much higher than that

*DOI: http://dx.doi.org/10.5772/intechopen.92069*

**2. Anti-nutritional factors**

from KTI [15].

**2.1 Phytase**

phytase.

**3. Cadmium content**
