Enhanced exopolysaccharide yield and antioxidant activities of <i>Schizophyllum commune</i> fermented products by the addition of Radix Puerariae

Abstract

To increase the production of exopolysaccharides (EPS) and expand the application of <i>Schizophyllum commune</i> (<i>S. commune</i>) fermentation liquid, the traditional Chinese medicine Radix Puerariae (RP) with outstanding biological activity was selected as a culture additive to improve the EPS yield and enhance the antioxidant activity of fermented products from <i>S. commune</i>. The effects of three independent factors: A: initial pH (5.0-6.0), B: concentration of RP (10-14 g L^-1), and C: inoculum size (8-12%, v/v) on the EPS yield were evaluated. The results of response surface methodology (RSM) showed that the optimal fermentation conditions were: A: 5.40, B: 12.80 g L^-1, and C: 10.0%. The optimal yield of EPS was 8.41 ± 0.12 mg mL^-1, which showed an insignificant (<i>p</i> > 0.05) difference with the predicted value (8.45 mg mL^-1). The fermented supernatants cultured from RP-supplemented medium (SC-RP) or regular medium (SC) were collected for further study. FT-IR analysis of EPS-1 (purified from SC) and EPS-2 (purified from SC-RP) showed that their structures were consistent, indicating that the addition of RP did not affect the structure of schizophyllan (SPG). In addition, compared with SC, the <i>in vitro</i> antioxidant activities of SC-RP were significantly improved with ORAC values and FRAP values increasing by 11.56-fold and 14.69-fold, respectively. There was a significant correlation among the phenolic compounds, flavonoids, and antioxidant activity of SC-RP in this study. Besides, SC-RP was detected to contain more than 25 bioactive ingredients compared with that of SC, which may play a key role in its antioxidant activities. Thus, these results indicated that RP enhanced the yield of SPG and improved the antioxidant activity of the fermented products by <i>S. commune</i>. Accordingly, the fermentation liquid of <i>S. commune</i> with the addition of RP may have potential application in food, cosmetics, and pharmaceutical industries.