Improvement of antioxidant activities of okara, a soybean by-product, through fermentation with Bacillus subtilis TISTR001

Abstract

Health benefit of okara which is a by-product from soymilk production can be improved by fermentation. This study aimed to ferment okara by Bacillus subtilis TISTR001. The effect of okara fermented with Bacillus subtilis TISTR001 on enzyme activities including alkaline protease, α-amylase, and β-glucosidase was investigated. Fermented okara was analyzed for total phenolic content, 2,2-diphenyl-l-pricrylhydrazyl (DPPH) radical scavenging activity, and 2,2-Azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) radical scavenging activity. After 96 h of fermentation, the highest alkaline protease (208.40 U/g), α-amylase (146.90 U/g), and β-glucosidase (10.81 U/g) activities were obtained from fermented okara by B. subtilis TISTR001 at the concentration of 7.0 Log CFU/g. Total phenolic compounds increased from 16.84 to 139.22 µg GAE/g, indicating higher antioxidant activities compared to unfermented okara. Meanwhile, the DPPH• free radical and ABTS•+ cation radical scavenging activities of the free and bound phenolic fractions in okara became stronger after fermentation. This indicated that the changes of antioxidant activities of phenolic fractions might be closely related to the structural modification by microbial enzymes in the fermented okara by B. subtilis TISTR001 at the highest concentration of cell biomass. The fermentation of okara with B. subtilis TISTR001 has shown to have a health-beneficial effect by enhancing its antioxidant properties.