**Abstract**

Soybeans have been cultivated as a traditional crop since ancient times in Japan, China, and other parts of Asia. Soybeans, as a source of protein, are rich in essential amino acids, but also contain a variety of functional and nutritional components. Their processed and fermented products support the maintenance of human health. Recently, new soybeans varieties containing superior nutritional components have been cultivated, and growing interest in plant-based foods has led to the establishment of new food products including dairy products such as butter and cream.

**Keywords:** soybeans, functional food, health benefits, protein, peptide, isoflavone, fat

## **1. Introduction: the origin of soybeans and their global production**

Soybean (*Glycine max* (L.) Merr.) is a traditional crop that contributes significantly in Asia's food culture. Several theories regarding the origin and spread of soybean have been suggested. Nevertheless, it has been reported that soybean was being cultivated in north-eastern China even 3000 years ago [1]. Currently, soybean is one of the most essential plant resources cultivated in various regions worldwide. The global production of soybeans in 2019 was approximately 340 million tons (**Figure 1**), making it one of the most commonly produced plant resources globally [2]. Approximately 80% of cultivated soybeans are used in livestock feed, and its majority is used for non-dietary purposes (i.e., printing ink, binder and resin dispersion, etc).

Soybean is known as the "miracle crop" as its actual cultivation initiated after 1930, mainly in the United States, and its production increased rapidly and significantly [3]. Soybean is widely cultivated in regions extending from the equatorial tropics up to southern regions of Sweden and Canada in the north, and Argentina and southern Australia in the south, with a substantial number of soybean varieties appropriate for cultivation in different environments and uses appropriate for each region.

#### **2. Functional components present in soybeans**

The composition of soybeans varies marginally depending on the variety; however, it commonly consists of protein (35–45%), fat (18–20%), and carbohydrates (22–28%), an insoluble fiber called okara, a low percentage of starch and sucrose, and some oligosaccharides such as stachyose and raffinose [4]. The physiologically

**Figure 1.** *World Soybean production.*

**Figure 2.** *Soybean composition.*

functional components of soybeans include vitamins such as K, A, B2, C, and D with a high content of vitamin E and B1 while they also contain glycosides in the form of isoflavones and saponins as well as functional lipids including lecithin and sterols.

Besides lipid-associated proteins, two types of globulins, 11S globulin and 7S globulin represent the two major components of soybean proteins (**Figure 2**) [4, 5]. With respect to the physiological function of soybean proteins, Carroll and Hamilton [6] reported in 1975 that consumption of soybean proteins reduces plasma low-density lipoprotein concentration. Sugano et al. [7] and Kohno [8] further elucidated the mechanism through which the indigestible high-molecularweight fraction of soybeans binds to excess bile acids in the intestinal tract and is excreted from the body. The U.S. Food and Drug Administration has approved the labeling of foods containing 25 g of soy protein per day as foods that reduce the risk of heart disease development due to the cholesterol-reducing effects of soy protein [9]. In Japan, soy protein represents a functional ingredient in food for special health-related use, and several correlated products are being commonly used [10]. It has been demonstrated that beta-conglycinin detected in 7S globulin reduces the visceral fat content and has been authorized for use in food for specific health-related use [11, 12].

*Present and Future Perspective of Soybean Cultivation DOI: http://dx.doi.org/10.5772/intechopen.103024*

Isoflavones, one of the essential components of soybeans, represent approximately 0.2–0.5% of seed weight, and their composition differ depending on the part of the soybean [13]. The isoflavone content per gram of protein in traditional soybean foods such as tofu is approximately 3.5 mg in aglycon units [14]. Isoflavones consist of genistein (~50%), daidzein (~40%), and glycitin (~10%). The physiological function (nonhormonal agent) of equal, a metabolite of daidzein ingested by the body and produced by intestinal microflora, is of particular scientific interest [15]. Isoflavones have been demonstrated to improve the blood lipid profile when consumed in combination with soy protein as a component of soy foods for a period of one to 3 months [16], and have shown to exert an anti-estrogenic effect on breast and prostate cancer that are hormone-related disorders [17, 18].

#### **3. Improvement of soybean characteristics via breeding**

Cultivation of soybean varieties suitable for different environments in various regions has been previously investigated, using high yield and pest resistance as the relevant development parameters. Development of soybeans with improved nutritional and functional characteristics has been pursued after utilizing wild species of soybean and employing genetic resources such as genetic mutations that are naturally generated during the cultivation process. Wild soybean (*Glycine soja* Sieb. et Zucc.) for instance, is characterized by its high protein and low-fat content. Yamada [19] reported that protein content (its main component) is adversely associated with its lipid content based on the examination of hybrids among this legume and soybean strains. Development of high protein soybeans by sacrificing a certain amount of the lipid content and agronomic traits would also be possible. Cultivation of soybeans including a higher protein content compared to conventional varieties is anticipated to contribute in the adaptation of soybean use products for protein intake, and for the improvement of productivity. Furthermore, it has been described that the 11S globulin content of soybeans increases when all 7S globulin genes are externally suppressed using microRNA [20]. Since 7S and 11S globulins are the main proteins in soybeans accounting for more than 50% of total protein content, changes on either protein levels result in significant effects on the gel water holding capacity, which is the main property of soybean protein. These proteins are thus expected to lead in the development of products that are completely different from conventional processed products from soybeans based on gelation properties.

Previous studies have attempted to enhance the content of alpha-tocopherol (α-Toc) and isoflavone through cultivation [21, 22]. Toc is a fat-soluble antioxidant commonly known as vitamin E. There are four naturally occurring homologs: α-, β-, γ-, and δ-Toc, with α-Toc being the most bioactive homolog. The total Toc content in soybean oil is relatively high among vegetable oils and fats. Nevertheless, the α-Toc content is low, ranging 5–7% [23] and as a result, vitamin E activity of soybean is not significant. Importantly, increasing the α-Toc content of soybeans has become a goal of cultivation. Dwiyanti et al. [21] demonstrated that gene expression related with α-Toc content was associated with the expression levels of one of the γ-Toc methyltransferase (E.C.2.1.1.95) isozyme (γ-TMT3) by genetic analysis of hybrids containing high α-Toc content using soybean genetic resources. In contrast, certain varieties have been identified in which α-Toc content increases from ×1.5 to ×5-fold during ripening in high temperature regions compared to that in standard regions [24], and an approach involving both genetic and cultivation environment is crucial when cultivating soybeans containing a high vitamin E content [24].

Various studies have also examined the potential of producing high-isoflavone soybeans [22, 25]. In isoflavone-related genetic analysis, it has been discovered that overexpression of the MYB transcription factor gene regulating the flavonoid biosynthetic pathway, increases the isoflavone and flavonol levels [26], suggesting the possibility of increasing isoflavone content via genetic engineering. In addition, a study has suggested that isoflavone content increases by ×3-fold when grown at a relatively lower temperature compared to that of standard growing conditions [26]. Isoflavone content may be thus increased by selecting varieties with genetic variation while considering the culturing conditions associated to the climate of the production area.
