Changes in isoflavone profiles and antioxidant activities in isoflavone extracts from soybeans and soyfoods under riboflavin photosensitization

Isoflavone extracts from soybeans and soyfoods were treated with riboflavin photosensitization and changes in antioxidant activities of isoflavone extracts under riboflavin sensitization were determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), and ferric reducing antioxidant power (FRAP) assays. Extracts rich in malonyl derivatives, β-glucosides, and aglycones were prepared from raw, ovendried, and almond-incubated soybeans, and the fermented soyfoods cheongukjang and natto. As the period of visible light irradiation increased to 120 min, the total isoflavone content determined using HPLC decreased in all samples. Aglycones in almond-incubated extracts decreased by 77.5% after 120min, and β-glucosides in oven-dried extracts decreased by 52.0%. The radical scavenging activity based on DPPH and ABTS assays significantly (p<0.05) decreased in most extracts, compared with controls. The reducing power in aglycone- and β-glucoside-rich extracts increased, whereas the reducing power in extracts with high malonyl forms was not significantly (p>0.05) increased after riboflavin sensitization.