Abstract:[Objective] This study aims to explore the effect of microbial fermentation on the active substances in Platycodonis Radix from Shangcheng. [Method] With the mass fractions of total flavonoids and total polyphenols as evaluation indicators, the dominant microbial strains were screened. The selected strain was subsequently applied to the fermentation of Platycodonis Radix from Shangcheng. Single-factor experiments and orthogonal experiments were conducted to optimize the critical fermentation parameters including time, temperature, solid-to-liquid ratio, and inoculum mass fraction. The effect of microbial fermentation on the antioxidant activity in vitro of Platycodonis Radix from Shangcheng was evaluated with DPPH free radical scavenging rate, ABTS+ free radical scavenging rate, and total reducing power as indicators. [Result] Aspergillus niger (A. niger) H was identified as the dominant strain for fermentation. The fermentation conditions were optimized as follows: fermentation with a solid-to-liquid ratio of 1 g∶5.5 mL and an inoculum mass fraction of 11% at 33 ℃ for 4 d. Under these conditions, the mass fraction of total flavonoids reached (5.32±0.13) mg/g (representing a 1.19-fold increase compared with that before fermentation) and that of total polyphenols achieved (156.88±0.88) mg/g (representing a 1.20-fold enhancement compared with that before fermentation). Platycodonis Radix from Shangcheng before and after fermentation showed the IC50 values of 0.030 mg/mL and 0.025 mg/mL for scavenging DPPH free radicals and 0.033 mg/mL and 0.021 mg/mL for scavenging ABTS+ free radicals, respectively. Total reducing power of Platycodonis Radix from Shangcheng was also substantially enhanced after fermentation. [Conclusion] The fermentation of Platycodonis Radix from Shangcheng with A. niger H could effectively improve the mass fractions of active ingredients and antioxidant capacity, which provided a theoretical basis for further research and development of Platycodonis Radix from Shangcheng.
