Quantitative Variation of Total Seed Isoflavone and its Compositions in Korean Soybean Cultivars (Glycine max (L.) Merr.)

The variation of content of 12 soybean seed isoflavone components was determined in the aglycone, glucoside, malonylglucoside and acetylglucoside groups of 44 Korean soybean cultivars grown in 2016 as well as in 2017. The total isoflavone content of the 44 cultivars averaged at $2935.4{\mu}g/g$ and was in the range of 950.6 to $5226.3{\mu}g/g$ for two years. Malonylglucoside group averaged at $2437.2{\mu}g/g$ with the highest proportion of isoflavone composition (83.0%). Significant differences were observed between cultivars, years and their interactions for both the total isoflavone and each composition group contents (P < 0.0001); however, no year-wise differences were observed for daidzein and genistin. The broad-sense heritability ($h^2$) within the set of 44 Korean soybean cultivars was as high as 0.93 for the total isoflavone content and was in the range of 0.8-0.92 for each composition group of isoflavone except for acetylglucoside. The total isoflavone content in cultivar group for soy-sprout was higher ($3850.4{\mu}g/g$) than that for the other cultivar groups of soy-paste and tofu ($3082.8{\mu}g/g$), black or green soybean cooked with rice ($2345.8{\mu}g/g$), and early maturity group ($1298.6{\mu}g/g$). The total isoflavone content of 'Sowonkong', a soybean cultivar for soy-sprout, was the highest ($5226.3{\mu}g/g$). In the cultivar group for soy-paste and tofu, the average isoflavone contents of 'Daepung', 'Daepung2ho', 'Saegeum', 'Uram', and 'Jinpung' were higher than $4000{\mu}g/g$. With the exception of small seeded cultivars with low isoflavone contents such as 'Sohwang' and 'Socheongja', the seed size and total isoflavone content were significantly negatively correlated in 2016 and 2017, respectively ($r=-0.47^{**}$ and $-0.49^{**}$). The number of days of growth from flowering to maturity did not affect the variations observed in isoflavone content.