A new sight on soy isoflavones during the whole soy sauce fermentation process by UPLC-MS/MS

Abstract

Soy sauce fermentation process includes koji-making and moromi fermentation stages, with the moromi stage consisting of solid (okara) and liquid (raw soy sauce) phases. Evolution of soy isoflavones in koji, okara and raw soy sauce samples was analyzed systematically, and the rule regarding the formation of soy isoflavones during the whole fermentation process was firstly figured out. Fifteen kinds of soy isoflavones were detected by UPLC-MS/MS. Following the fermentation process, the soy isoflavones profiles changed dramatically in the initial moromi stage (1 d-15 d). The concentrations of glucosides, malonylglucosides and acetylglucosides decreased and disappeared around at okara-30 d, while the concentrations of aglycones and hydroxyl aglycones increased and attained the peak at 90 d of the moromi stage. Additionally, antioxidant capacities of samples were positively correlated with the concentrations of aglycones and hydroxyl aglycones. Interestingly, in each sample, the antioxidant contribution value of hydroxydaidzein was around 100–500 times higher than that of daidzein, which demonstrated that aglycones, especially hydroxyl aglycones, were the key isoflavones contributed to the antioxidant properties of soy sauce.