Effect of harvest time of day on the isoflavone synthesis pathway in immature soybeans

Isoflavones, such as daidzein and genistein, are abundant in soybeans. As isoflavones have many beneficial health effects, the development of methods to increase the amounts of these compounds is important. In this study, the effect of harvest timing on expression patterns of isoflavone synthase (IFS) and cinnamate 4-hydroxylase (C4H), two major genes in the isoflavone synthesis pathway, in the pulp of immature soybeans from an open-air field were evaluated. The immature soybeans were collected at five different time points over a 24-hour period, and the gene expressions and isoflavone amounts were analyzed using reverse transcription-PCR and HPLC-diode array detector, respectively. The results showed that C4H expression increased during the day and decreased at night, although IFS expression tended to decrease during the middle of the night, but not significantly. Whereas isoflavone content was decreased during the day. These results suggested the possibility that the harvest of immature soybeans immediately after sunset is desirable for increasing isoflavone amounts.