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

Abstract

To increase the production of exopolysaccharides (EPS) and expand the application of Schizophyllum commune (S. commune) 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 S. commune. 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 (p > 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 in vitro 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 S. commune. Accordingly, the fermentation liquid of S. commune with the addition of RP may have potential application in food, cosmetics, and pharmaceutical industries.

Fig. 1. Schematic representation of the preparation of EPS from the fermented supernatants cultured from RP-supplemented medium (SC-RP) or regular medium (SC).

Fig. 2. Infrared spectra of EPS purified from fermented supernatants cultured from regular medium (EPS-1) and RP-supplemented medium (EPS-2).

Fig. 3. Effect of each variable factor on the yield of EPS and biomass: (a) initial pH; (b) Radix Puerariae content; (c) inoculum size; and (d) fermentation period. Data is expressed as mean ± SD, n = 3. ^a Values with no letters in common are significantly different (p < 0.05).

Fig. 4. Normal probability plot of residuals of the predictable values (a), and the predicted and actual response slope (b) of EPS yield from Schizophyllum commune.

Fig. 5. Three-dimensional plots and corresponding contour plots of the three variables (A: initial pH; B: Radix Puerariae contents; and C: inoculum size) on the response of EPS yield.

Fig. 6. In vitro antioxidant capability of the fermented supernatants cultured from RP-supplemented medium (SC-RP) or regular medium (SC). (a: Hydroxyl radical scavenging activities; b: ABTS radical scavenging activities; c: FRAP values; and d: ORAC values). Data is expressed as mean ± SD, n = 3. ^a Values with no letters in common are significantly different (p < 0.05).

Fig. 7. Schematic diagram of the ultrafiltration membrane separation process. (1-Beaker; 2-circulating pump; 3-pressure gage; 4-membrane module; and 5-pressure gage.)

Fig. 8. In vitro antioxidant capacity of different molecular weights of the fermented supernatants cultured from RP-supplemented medium (SC-RP) or regular medium (SC). (a: Hydroxyl radical scavenging activities; b: ABTS radical scavenging activities; c: FRAP values; and d: ORAC values). Data is expressed as mean ± SD, n = 3. ^a Values with no letters in common are significantly different (p < 0.05).