Enhanced antioxidative activity of Chinese traditionally fermented Okara (Meitauza) prepared with various microorganism

In order to investigate the antioxidative activity of Meitauza koji (Meitauza, a Chinese traditionally fermented okara), the okara was fermented with Aspergillus oryzae 3.951, Rhizopus oligosporus 3.912, Actinomucor elegans 3.118 and Bacillus subtilis B2 as kojis. All the methanol extract yields and peptide content of the kojis were higher than that of non-fermented okara. Moreover, the Meitauza kojis displayed enhanced antioxidative activities in comparison with the non-fermented okara. Among the four kinds of kojis tested, those fermented with B. subtilis B2 exhibited the highest levels of 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals scavenging activities and reducing power. The ABTS and DPPH radicals scavenging activities of Meitauza koji fermented with B. subtilis B2 were ca. 12.53 and 7.92 folds that of the non-fermented okara. Analysis of the dose-response effect also revealed that before reaching a threshold point, there is a linear relationship between increases in antioxidative activity and increases in the concentration of koji extract. In addition, the peptide content of the Meitauza koji prepared with B. subtilis B2 increased from 8.6 mg to 34 mg per 100 mg extract. These results suggest the potential for developing traditional functional food with okara fermented by B. Subtilis B2.