Characterization of Isoflavone Conjugated Metabolites in Human Plasma and Urine by Dietary Soybean Meals

Objectives Soy isoflavones are one of the best studied secondary plant metabolites for the last 30 years and associated with potential health benefits such as prevention of cancer, cardiovascular diseases, and menopausal symptoms. The study aimed to identify isoflavone conjugated metabolites from human plasma and urine after dietary soybean meals using a targeted metabolomic approach and to investigate the effect of fermentation on bioavailability of soy isoflavones. Methods In the cross-over intervention design with 10 candidates (6 women and 4 men), standardized meals with fermented soybean (FS, Cheonggukjang, by Bacillus subtilis) and non-fermented soybean (NFS) were served over two weeks in two randomized groups. Flavonoid derivatives in each freeze-dried tested meal and isoflavone conjugated metabolites in plasma and urine collected before and after the consumption of each meal were evaluated by UPLC-DAD-QToF/MS. Results Twenty-two isoflavones, including genistein, daidzein, glycitein, and its glycosides, were identified in both tested meals. In particular, 6”-O-succinoyldadizin and 6”-O-succinoylgenistin produced newly as acylated forms with succinic acid in fermented process. Also, in levels of simple glycosidic forms (e.g., daidzin and genistin), the FS meal showed higher than NFS meal, which might be explained by the degradation of malonylglucosides during the fermentation. Fourteen metabolites conjugated with glucuronic acid and sulfuric acid were identified in plasma and urine, among them, genistein 4’,7-di-O-glucuronide and daidzein 7-O-glucuronide were confirmed as major metabolites in plasma and urine, respectively. The bioavailability was differentiated by personal characteristics after intake soy isoflavones, and it was considered that genistein class was more excellent as well as FS meal was more effective when compared to NFS meal on bioavailability. Conclusions The results may contribute to not only understanding the potential health effects of fermented foods by modifying the bioavailability of soybean bioactive components but also application of other traditional foods related with fermentation. Funding Sources This work was supported by the National Institute of Agricultural Science of Rural Development Administration, Republic of Korea.