Variation of Chemical Components and Their Interaction with Isoflavones in Maturing Soybean Seeds

This study was focuses on the variation of isoflavone contents during seed development and their interaction with major chemical components such as protein, amino acids, saccaharides, lipid and fatty acids. During maturing, lipid, protein, and amino acid contents in soybean seeds showed the highest values at R7 stages, but isoflavone contents were increased until R8 stage. It was noted that malonyl glucosides $(64.2\%)$ are predominant forms among conjugated isoflavones followed by glucosides $(30.7\%)$, acetyl glucosides $(4.1\%)$ and aglycones $(0.9\%)$. Sucrose and stachyose were presented as a major saccharide in soybean seeds. As maturing days progressed, they were constantly increased and the highest contents were observed at R8 stage. While small quantities of raffinose, fructose, glucose, maltose, DP3 (DP: degree of polymerization), DP6, and DP7 were detected. These results showed that saccharide composition at the beginning of seed development is primarily monosaccharides with little sucrose and oligosaccharides, but as maturing days proceeds, sucrose and starch increase with concomitant decrease in monosaccharides. Sucrose and stachyose were positively correlated with isoflavone (r=0.780, 0.764 at p<0.01, respectively), while fructose, glucose, maltose, and DP7 were negatively correlated (r=-0.651, -0.653, -0.602, and -0.586 at p<0.05, respectively). Soybeans at R8 stage were high in protein and amino acid, but low in free amino acid contents. Protein and amino acid contents showed positively significant correlations with isoflavone (r=0.571 and 0.599 at p<0.05, respectively), but free amino acid content were negatively correlation with isoflavone (r=-0.673, p<0.01). The lipid content reaches its final content relatively early stage of seed development and remains constant as compared with other chemical components. Among the fatty acids, although varietal difference was presented, stearic acid and linolenic acid were gradually decreased, while oleic and linoleic acid were increased as seed maturing progressed. Lipid was significantly correlated (r=0.754, p<0.01) with isoflavones. However, neither saturated fatty acid nor unsaturated fatty acids significantly affected the isoflavone contents of maturing soybean seeds.