**11. Breeding for functional components**

#### **11.1 Lipoxygenase**

Normal soybean seeds contain three lipoxygenase isozymes that are responsible for the grassy beany flavor and bitter taste of soy food. Research is being conducted for the genetic elimination of lipoxygenase from soybean seeds to reduce undesirable flavors in soy food products. Soybean seed lipoxygenase exists in three isozymic forms, namely lipoxygenase-1, −2, and −3 controlled by single dominant genes, viz. *Lx1*, *Lx2*, and *Lx3*, respectively. Their recessive forms, i.e., *lx1*, *lx2*, and *lx3* cause the loss in activity of corresponding isozyme [119]. Several combinations of lipoxygenase null mutants have already been developed: 0-, 00-, and 000-genotypes with one, two, and three of the isozymes eliminated respectively, In the 000-genotype, absence of the grassy and beany flavor was observed, as there was no detectable level of the lipoxygenase proteins in mature soybean seeds. The presence or absence of three lipoxygenase isozymes is determined by gel electrophoresis and spectrophotometer or by immunological or colorimetric methods [13]. Of the three lipoxygenases, *Lx2* locus has been mapped on *chr13*, which corresponds to linkage group F, and has been reported tightly linked with *Lx1* locus [120]. *Lx3* gene has been reported to be present on *chr15* and is inherited independent of *Lx1* and *Lx2.* SSR marker Satt656 tightly linked with Lox2 [121] has been deployed in the development of Lox-2 free soybean genotypes NRC109 and NRC110 in India [121].

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

were developed for identification of Lox*3* null individual [122].

Based on *Lx3* mutant gene sequence, SNP (Lox3PM1) and STS marker (Lox3–3′)

Soybean cultivars with good isoflavone content are desirable as it contributes health benefits. High-isoflavone soybeans contain more than 0.4% isoflavones compared to levels of 0.15–0.25% for traditional soybean varieties [13]. Isoflavone content is influenced by genetic factors and environmental factors such as temperature and irrigation during seed maturation [13]. For instance, the total isoflavone content of soybean seeds appears to be negatively related to growth temperature [5]. Understanding the genetic regulation of this pathway may be necessary for obtaining cultivars with good isoflavone levels. Interest has been put in the phenylpropanoid synthetic pathway which is catalyzed in its first step by isoflavone synthase (IFS). Two genes for IFS have been identified in soybean. Furthermore, negative correlation has been found between total isoflavone content and linolenic acid (18:3) concentration. Other data suggest negative correlation between isoflavone content and protein content [5]. QTLs affecting isoflavones were identified using recombinant inbred line population and found five QTLs contributed to the concentration of isoflavones, having single or multiple additive effects on isoflavone component traits [123]. Similarly, six QTLs were identified using the linkage map constructed with specific length amplified fragment sequencing, of which one major QTL (qIF20-2) contributed to a majority of isoflavone components across various environments and explained a high amount of phenotypic variance (8.7–35.3%) [124]. Akond et al. [125] identified QTL controlling isoflavone content in a set of recombinant inbred line (RIL) populations of soybean derived from "MD96–5722" by "Spencer" cultivars. Wide variations were found for seed concentrations of daidzein, glycitein, genistein, and total isoflavones among RIL populations. Three QTLs were identified on three different linkage groups (LG). One QTL that controlled daidzein content was identified on LG A1 (Chr 5) and two QTLs that underlay glycitein content were identified on LG K (Chr 9) and LG B2 (Chr 14). Identified QTLs could be used to develop soybean with preferable isoflavone

Increasing the seed oil concentration has been a breeding goal for centuries. The ancestor of the domesticated soybean used to have small, hard, black seeds with low oil content, high protein content, and low yield. It is known that an increase in oil content is positively correlated with yield and negatively correlated with protein content. Selection for yield, agronomic characteristics and seed quality, large yellow seeds with typical averages of 20% oil and 40% protein were obtained. However, soybean is appreciated for its high protein meal and versatile vegetable oils; therefore, breeders mostly prefer to obtain modest gains in oil and yield without substantial loss in protein concentration [42]. Breeding for oil quality such as with reduced saturated fatty acids are prime focus as it is responsible for elevating cholesterol. The saturated fatty acids present in soybean oil are palmitic acid, 16:0, and stearic acid, 18:0. Especially, palmitic acid is a health concern as it is correlated to cardiovascular disease. It has been suggested that saturated fatty acids should be kept below 7–10% on a daily basis [42]. Soybean oil contains the monounsaturated fatty acid, oleic acid, 18:1. The oxidative stability of the soybean oil is enhanced by increasing three times higher the concentration of monounsaturated fatty acid such as oleic (18:1) than the normal content which is about 22%. Therefore, breeders target a concentration of 18:1 of about 65–75% of total lipid in soybean. By the means

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

concentrations in the seeds through MAS.

**11.3 Seed oil concentration**

**11.2 Isoflavones**

Based on *Lx3* mutant gene sequence, SNP (Lox3PM1) and STS marker (Lox3–3′) were developed for identification of Lox*3* null individual [122].
