Improvement of the antioxidant activity of Chinese traditional fermented okara (Meitauza) using Bacillus subtilis B2

To evaluate the antioxidant activity of Chinese traditional fermented okara (Meitauza), Bacillus subtilis B2 was used to ferment okara to obtain the Meitauza in the present study. The peptide content, proteinase activity, degradation of protein of the water extract of okara koji (WEOK) and the antioxidant activities in different in vitro models were investigated. Compared with the water extract of soybean koji (WESK), WEOK showed higher 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and reducing power, and both the linoleic acid radical scavenging activity and 2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) scavenging activity of WEOK were almost equal with those of WESK. The peptide and the antioxidant activity in WEOK are significantly correlated (P < 0.05). The proteinase activity of okara koji was higher than that of soybean koji in the first 24 h of fermentation. These data suggested that the antioxidant activity of okara could be substantially improved after 24 h of fermentation using B. subtilis B2. This approach offers a novel strategy to enhance the value of okara.