**4. Nutritional factors**

#### **4.1 Soybean protein**

Soybean contains about 40% protein and is noteworthy as it is the most complete vegetable protein [25]. Concretely, with exception of sulfur-containing amino acids such as methionine, the amino acid pattern of soybean resembles the pattern derived from high-quality animal protein sources [25]. In fact, soybean protein can even enhance the nutritional quality of other vegetable protein. Protein sources that are deficient in some amino acids can be complemented by soybean. Soybean is rich in lysine, tryptophan, threonine, isoleucine, and valine and therefore complements well with cereal grains that are deficient in those amino acids [26]. By ultracentrifugation studies, four different fractions have been revealed, with approximate Svedberg coefficients of 2S, 7S, 11S, and 15S [6]. The 2S fraction contains from 8 to 22% of the extractable soybean protein. It consists of several enzymes, including the trypsin inhibitors, Bowman-Birk and Kunitz inhibitors [6]. Trypsin inhibitors inhibit the protein-cleavage effect of proteases (such as trypsin) affecting the digestibility and leading to growth depression in animals. Therefore, soybean meal needs first to be heated in order to inactivate the trypsin inhibitors. However, trypsin inhibitors have been found to be powerful anti-carcinogenic agents in humans and therefore they can be considered as functional components of soybeans [27].

More than 70% of the soybean seed storage protein is composed of 7S β-conglycinin and 11S glycinin. The 7S fraction makes up 35% of the extractable soybean protein. The quantity and the quality of the protein in the seed are the major biochemical components influencing the quality of tofu and other soy food products [28]. The mean glycinin to β-conglycinin protein ratio is known to influence the protein quality of soybeans, and greatly affects the functional properties of food products made from soybeans [29, 30]. Glycinin and β-conglycinin also differ in amino acid composition, with glycinin being higher in sulfur (S), containing amino acids that account for 3–4.5% of the total amino acid residues [31]. G1, G2, and G7 glycinin subunits contain a higher amount of methionine (6–7 per subunit) compared to G3, G4, and G5 glycinin subunits, which contain 5, 2, and 4 methionine residues per subunit, respectively [31]. By comparison, β-conglycinin is devoid of methionine [32, 33] and β-conglycinin contains a major allergen in its subunit [34]. Increased glycinin content in soybean protein is an important trait for increasing the concentration of the S-containing amino acids [35]. Because glycinin and β-conglycinin have a great impact on the nutritional value and quality of soybean products, these two storage proteins have been extensively studied and targeted for genetic manipulation in breeding programs. Soybean mutant genotypes differing in seed storage glycinin and β-conglycinin subunit composition were developed and tested for their effects on tofu quality [30]. It was shown that group IIb (A3) glycinin played the major role in contributing to tofu firmness with any coagulant, while the group IIa (A4) subunit could have a negative effect on tofu quality. Yu et al. [36] reported that soybean cultivars with 7S α′ and 11 S a4 nulls always make firm tofu than the check cultivar Harovinton. The hardness of gels from glycinin

**55**

**4.3 Soybean oil**

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

be composed of polymers of the other soybean proteins [6].

**4.2 Carbohydrates**

also affects the quality and stability of soymilk [39].

decreased in the order of group IIa, IIb, and I [37, 38]. Protein subunit composition

Other soybean seed proteins include lipoxygenase and lectins. The lipoxygenase enzyme constitutes about 1–2% of the soybean protein. The lipoxygenase enzyme generates a grassy-beany flavor when it oxidizes fats and is not preferred by consumers in some countries. It is possible to avoid the oxidation of the fats by heat inactivation of the lipoxygenase enzyme; however, this is cost-ineffective and leads to insolubilization of proteins. Therefore, the genetic elimination of the lipoxygenase is preferred in order to reduce the beany flavor. Genotypic variation and the influence of growing environment on lipoxygenase accumulation in soybean seed are well documented in the literature [2, 26]. Lipoxygenase 1, 2, and 3 null germplasm lines were developed and showed that the grassy-beany flavor was eliminated [40]. Triple-null soybeans can be used for edible soy products, such as soymilk and tofu [40]. Similarly, saponins and isoflavones may also be the cause of undesirable taste in soy products although this is not well documented yet. The breeding of cultivars with low isoflavones and saponins is possible [2]. The 11S fraction comprises 31–52% of the extractable soybean proteins [6]. The 11S fraction is responsible for the gelling character of tofu, and hence, the proportion of this fraction compared to 7S plays an important role in tofu firmness [2]. The 15 S fraction comprises about 5% of the total extractable protein. It is only poorly characterized and is thought to

Dry soybeans contain on average 35% of carbohydrates, which can be divided into soluble and insoluble carbohydrates [27]. Soybean seeds possess 15–20 different soluble carbohydrates that makes up approximately 15–25% of dry weight [41]. Sucrose, raffinose, and stachyose are the most relevant soluble carbohydrates for breeding of food-grade soybean. Sucrose in dry soybean seeds is found in contents of typically 5.5% [27]. Sucrose is important for improving taste in soybean-based products. The oligosaccharides raffinose and stachyose typically constitute about 0.9 and 3.5% of dry soybean seeds, respectively [27]. The seed coat of soybeans contains a major part of insoluble carbohydrates such as cellulose, hemicellulose, pectin, and a trace amount of starch [27]. Consumers, especially in countries where fermented and vegetable soybean are not in vogue, may be skeptical toward the use of soy products because of flatulence and poor digestibility. These effects are caused by oligosaccharides, stachyose and raffinose. Humans and monogastric animals do not possess the enzyme called α-galactosidase necessary for hydrolyzing the linkages present in these oligosaccharides, so they cannot be digested when consumed. Intact oligosaccharides reach the lower intestine and undergo anaerobic fermentation by bacteria with gas expulsion (H2, CO2, and traces of CH4), causing the flatus effect and sometimes diarrhea and abdominal pain. Although raffinose and stachyose can be reduced to an extent by soaking or boiling, genetic reduction is one of the prime plant breeding objectives.

The major components of crude soybean oil are triglycerides. After refinement of the oil, soybean oil is composed of 99% of triglycerides. Triglycerides are neutral lipids composed of one glycerol linking three fatty acids [27]. The saturated fatty acids in soybean oil are palmitic acid (16:0) and stearic acid (18:0), with average concentrations of about 11 and 4% (relative to the oil), respectively, and they are useful in making low trans-fat margarines. Soybean oil contains an average of

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

#### *Food Grade Soybean Breeding, Current Status and Future Directions DOI: http://dx.doi.org/10.5772/intechopen.92069*

decreased in the order of group IIa, IIb, and I [37, 38]. Protein subunit composition also affects the quality and stability of soymilk [39].

Other soybean seed proteins include lipoxygenase and lectins. The lipoxygenase enzyme constitutes about 1–2% of the soybean protein. The lipoxygenase enzyme generates a grassy-beany flavor when it oxidizes fats and is not preferred by consumers in some countries. It is possible to avoid the oxidation of the fats by heat inactivation of the lipoxygenase enzyme; however, this is cost-ineffective and leads to insolubilization of proteins. Therefore, the genetic elimination of the lipoxygenase is preferred in order to reduce the beany flavor. Genotypic variation and the influence of growing environment on lipoxygenase accumulation in soybean seed are well documented in the literature [2, 26]. Lipoxygenase 1, 2, and 3 null germplasm lines were developed and showed that the grassy-beany flavor was eliminated [40]. Triple-null soybeans can be used for edible soy products, such as soymilk and tofu [40]. Similarly, saponins and isoflavones may also be the cause of undesirable taste in soy products although this is not well documented yet. The breeding of cultivars with low isoflavones and saponins is possible [2]. The 11S fraction comprises 31–52% of the extractable soybean proteins [6]. The 11S fraction is responsible for the gelling character of tofu, and hence, the proportion of this fraction compared to 7S plays an important role in tofu firmness [2]. The 15 S fraction comprises about 5% of the total extractable protein. It is only poorly characterized and is thought to be composed of polymers of the other soybean proteins [6].

#### **4.2 Carbohydrates**

*Legume Crops - Prospects, Production and Uses*

practices [24].

**4. Nutritional factors**

**4.1 Soybean protein**

human consumption. Cd uptake depends both on the Cd concentration in the soil and on the characteristics of the specific cultivars. Breeding cultivar with reduced Cd is an attractive method for changing the element profile of crops as the benefit will persist in the seed that can reduce the requirement for other management

Soybean contains about 40% protein and is noteworthy as it is the most complete vegetable protein [25]. Concretely, with exception of sulfur-containing amino acids such as methionine, the amino acid pattern of soybean resembles the pattern derived from high-quality animal protein sources [25]. In fact, soybean protein can even enhance the nutritional quality of other vegetable protein. Protein sources that are deficient in some amino acids can be complemented by soybean. Soybean is rich in lysine, tryptophan, threonine, isoleucine, and valine and therefore complements well with cereal grains that are deficient in those amino acids [26]. By ultracentrifugation studies, four different fractions have been revealed, with approximate Svedberg coefficients of 2S, 7S, 11S, and 15S [6]. The 2S fraction contains from 8 to 22% of the extractable soybean protein. It consists of several enzymes, including the trypsin inhibitors, Bowman-Birk and Kunitz inhibitors [6]. Trypsin inhibitors inhibit the protein-cleavage effect of proteases (such as trypsin) affecting the digestibility and leading to growth depression in animals. Therefore, soybean meal needs first to be heated in order to inactivate the trypsin inhibitors. However, trypsin inhibitors have been found to be powerful anti-carcinogenic agents in humans and therefore they can be considered as functional components of soybeans [27]. More than 70% of the soybean seed storage protein is composed of 7S β-conglycinin and 11S glycinin. The 7S fraction makes up 35% of the extractable soybean protein. The quantity and the quality of the protein in the seed are the major biochemical components influencing the quality of tofu and other soy food products [28]. The mean glycinin to β-conglycinin protein ratio is known to influence the protein quality of soybeans, and greatly affects the functional properties of food products made from soybeans [29, 30]. Glycinin and β-conglycinin also differ in amino acid composition, with glycinin being higher in sulfur (S), containing amino acids that account for 3–4.5% of the total amino acid residues [31]. G1, G2, and G7 glycinin subunits contain a higher amount of methionine (6–7 per subunit) compared to G3, G4, and G5 glycinin subunits, which contain 5, 2, and 4 methionine residues per subunit, respectively [31]. By comparison, β-conglycinin is devoid of methionine [32, 33] and β-conglycinin contains a major allergen in its subunit [34]. Increased glycinin content in soybean protein is an important trait for increasing the concentration of the S-containing amino acids [35]. Because glycinin and β-conglycinin have a great impact on the nutritional value and quality of soybean products, these two storage proteins have been extensively studied and targeted for genetic manipulation in breeding programs. Soybean mutant genotypes differing in seed storage glycinin and β-conglycinin subunit composition were developed and tested for their effects on tofu quality [30]. It was shown that group IIb (A3) glycinin played the major role in contributing to tofu firmness with any coagulant, while the group IIa (A4) subunit could have a negative effect on tofu quality. Yu et al. [36] reported that soybean cultivars with 7S α′ and 11 S a4 nulls always make firm tofu than the check cultivar Harovinton. The hardness of gels from glycinin

**54**

Dry soybeans contain on average 35% of carbohydrates, which can be divided into soluble and insoluble carbohydrates [27]. Soybean seeds possess 15–20 different soluble carbohydrates that makes up approximately 15–25% of dry weight [41]. Sucrose, raffinose, and stachyose are the most relevant soluble carbohydrates for breeding of food-grade soybean. Sucrose in dry soybean seeds is found in contents of typically 5.5% [27]. Sucrose is important for improving taste in soybean-based products. The oligosaccharides raffinose and stachyose typically constitute about 0.9 and 3.5% of dry soybean seeds, respectively [27]. The seed coat of soybeans contains a major part of insoluble carbohydrates such as cellulose, hemicellulose, pectin, and a trace amount of starch [27]. Consumers, especially in countries where fermented and vegetable soybean are not in vogue, may be skeptical toward the use of soy products because of flatulence and poor digestibility. These effects are caused by oligosaccharides, stachyose and raffinose. Humans and monogastric animals do not possess the enzyme called α-galactosidase necessary for hydrolyzing the linkages present in these oligosaccharides, so they cannot be digested when consumed. Intact oligosaccharides reach the lower intestine and undergo anaerobic fermentation by bacteria with gas expulsion (H2, CO2, and traces of CH4), causing the flatus effect and sometimes diarrhea and abdominal pain. Although raffinose and stachyose can be reduced to an extent by soaking or boiling, genetic reduction is one of the prime plant breeding objectives.

#### **4.3 Soybean oil**

The major components of crude soybean oil are triglycerides. After refinement of the oil, soybean oil is composed of 99% of triglycerides. Triglycerides are neutral lipids composed of one glycerol linking three fatty acids [27]. The saturated fatty acids in soybean oil are palmitic acid (16:0) and stearic acid (18:0), with average concentrations of about 11 and 4% (relative to the oil), respectively, and they are useful in making low trans-fat margarines. Soybean oil contains an average of

22% monounsaturated fatty acid, oleic acid (18:1). Monounsaturated fatty acids are healthy and have good oil stability [42]. Soybean oil possesses the two polyunsaturated fatty acids: linoleic acid (18:2), an omega-6 fatty acid, and linolenic acid (18:3), an omega-3 fatty acid [26]. They can be found in average concentrations of 53 and 8% of the oil, for linoleic and linolenic acid, respectively. Low (reduced) linolenic soybeans have half the linolenic acid level of standard soybeans, which reduces the need for hydrogenation, a process used in converting vegetable oils to margarine that results in the production of unhealthy trans fatty acids.

Soybean crude oil is also shown to consist of phospholipids, unsaponifiable material, free fatty acids, and metals. Unsaponifiable material consists of tocopherols, phytosterols, and hydrocarbons [27]. Tocopherols and phytosterols are considered as functional components. Soybean oil provides an additional benefit due to presence of enriched amounts of α-tocopherol or natural vitamin E. Oils containing low contents of linolenic acid (18:3) have been shown to contain high amount of α-tocopherol and results in lowered amount of ϒ-tocopherol [5].

#### **4.4 Vitamins and minerals**

Soybeans contain water-soluble and oil-soluble vitamins. The water-soluble vitamins such as vitamin B1 (thiamin), vitamin B2 (riboflavin), vitamin B5 (pantothenic acid), and vitamin B6 (niacin) and the oil-soluble vitamins vitamin A and vitamin E (tocopherols) are present in soybean. Vitamin A mainly exists in the form of β-carotene in immature and germinated seeds, whereas it is present in negligible amount in mature seeds [27]. Most of the minerals are found in the meal fraction rather than in the soybean oil fraction. Dry soybean seeds contain on an average concentration ranging from 0.2 to 2.1% major minerals such as potassium, which is present in the highest concentration followed by phosphorus, magnesium, sulfur, calcium, chloride, and sodium [27]. Minor minerals found in soybeans include silicon, iron, zinc, manganese, copper, molybdenum, fluorine, chromium, selenium, cobalt, cadmium, lead, arsenic, mercury, and iodine [27].

#### **4.5 Functional components**

Functional components of soybeans include isoflavones, saponins, lecithin, trypsin inhibitors, lectins, oligosaccharides, tocopherols, and phytosterols [27]. Presence of such biological ingredient creates interest to consider soybean food products as functional foods, i.e., foods that contain biological components that deliver special health benefits, e.g., anticancer, hypocholesteromic, and antioxidative effects to the consumer [26]. Isoflavones are phytoestrogens and are known to have positive health effects such as the reduction of the risks for coronary heart disease, osteoporosis, certain types of cancer, and the moderation of postmenopausal symptoms in women [43]. Soybean possesses 0.1–0.4% of isoflavones on a dry weight basis; hence, soybean possesses the highest amount of isoflavones compared to all other crops [27]. The isoflavone concentration varies considerably depending upon the genotype and environmental conditions. It is thought that isoflavones are mainly responsible for most of the health benefits from soybean-based foods. Therefore, they gained more and more attention from the scientific world [27], and research on breeding for enhanced isoflavone content is increasing. Refined soybean oil possesses about 1000–2000 mg/kg. Tocopherol exists in four isomers, three of them being α-, ϒ-, and δ-isomers that are present in soybean oil. α-tocopherol (natural vitamin E) in soybean is the leading commercial source of this vitamin. Tocopherols protect the polyunsaturated fatty acids from oxidation; hence, they are antioxidants and used in pharmaceutical applications [42].

**57**

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

Soybeans with large seed size and high protein levels are primarily used for soymilk and tofu production. Other traditional food from soybean includes tempeh, miso, soy sauce, okara, soynuts, soy milk, yoghurt, meat, and cheese alternatives. Tofu is perhaps the most widely consumed soy food in the world. Tofu is naturally processed and it retains a good amount of nutrients and phytochemicals such as the isoflavones [5]. Tofu typically contains 7.8% protein and 4.2% lipid on a wet basis [5]. It has a relatively low carbohydrate and fiber content, making it easier to digest. There are two main types of tofu: silken, or soft tofu and hard tofu. They are made by soaking whole soybeans and grinding them into a slurry with water. The slurry is cooked to form soymilk and a coagulant is added. The most commonly used coagulants are magnesium chloride, calcium sulfate, or glucono-D-lactone; the coagulants can be used purely or in combinations to achieve different flavor or textural characteristics. Heating is also usually applied in order to facilitate the coagulation. The result of the coagulation is that after a few minutes, the soymilk begins to curdle and large white clouds of tofu curd are formed. The water in the curds are then removed and placing the tofu curd in cloth-lined forming boxes where pressure is applied from the top results in the formation of hard tofu. Silken tofu in comparison to hard tofu is not pressed and is often coagulated in the container in which it is to be sold. [2].

The popularity of soymilk has expanded from Asia to the U.S. and Europe since the 1980s. Traditionally, it is made from whole beans in the same way as the first few steps of tofu manufacture. This soy milk contains nutrients, saponins, isoflavones, and other soluble components of the soybean from which the soy milk is made. Some manufacturers add isoflavones back into the soy milk in order to make health claims about the product. Additionally, soymilks are also fortified with vitamins and minerals, such as β-carotene and calcium or docosahexaenoic acid (DHA), an omega-3 fatty acid [2]. However, beverage-quality soy milks available in the market are usually prepared from soy protein isolate, to which sugars, fats, and carbohydrates are added to improve flavor and generate a nutritional profile similar to that

Vegetable soybean consists of the whole soybean picked at the R6-R7 stage and seeds are bigger and sweeter. At this stage, the soybean has a firm texture, contains a high level of sucrose, chlorophyll, and is at its peak of green maturity. The harvested pod can be left entire or be shucked into individual beans. After being blanched and frozen, the soybean can be sold as "edamame," referring to the entire pod, or "mukimame," referring to individual beans [2]. Nutritionally, it is highly rich in protein (11–16%), monounsaturated fatty acid, vitamin C, fiber, iron, zinc, calcium, phosphorous, folate, magnesium, potassium, tocopherol, and anticancer isoflavones [44]. It also has a pleasant flavor and soft texture and is easier to cook. Cooked vegetable soybean has the highest net protein utilization value (NPU: ratio of amino acid converted to protein) among all soy products. Vegetable soybean also has 60% more calcium and twice the phosphorus and potassium levels of green peas, which is India's most commonly consumed fresh legume (https:// www.gov.uk/government/case-studies/dfid). The vegetable soybean, in general,

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

**5. Soyfoods**

**5.2 Soymilk**

of cow's milk [2].

**5.3 Vegetable soybeans (edamame, mukimame)**

**5.1 Tofu**
