Effect of low-frequency alternating magnetic field on exopolysaccharide production and antioxidant capacity of Pleurotus citrinopileatus by submerged fermentation.

The objective of this study was to investigate the effect of low-frequency alternating magnetic field (LF-AMF) on the production of extracellular polysaccharide (EPS) by submerged fermentation of Pleurotus citrinopileatus. The fermentation conditions optimized by the central composite design method were as follows: fermentation time of 6.18 days, temperature of 28.28 °C, shaking speed of 149.04 r/min, and inoculum amount of 8.43%. Under these conditions, a LF-AMF was applied to the submerged fermentation of P. citrinopileatus. When the intensity of LF-AMF was 40 Gs, the initial intervention time was 24 h after inoculation, and the treatment time was 6 h at one time, the mycelial biomass of P. citrinopileatus increased by 11.30%, and the EPS yield increased by 23.09% compared with the fermentation without LF-AMF treatment. The morphology of mycelium after LF-AMF treatment was observed by scanning electron microscopy. It was found that the surface of mycelium was wrinkled, and the structure of mycelium was loose, which might be more conducive to the production of EPS. Mycelium diameter decreased, and ATPase activity increased, indicating that LF-AMF had a positive effect on the production of EPS by P. citrinopileatus fermentation. Moreover, LF-AMF could improve the permeability of the mycelial cell membrane, facilitate the exchange of intracellular and extracellular substances, and increase the metabolic capacity of P. citrinopileatus. In vitro antioxidant test of EPS showed that LF-AMF treatment also improved its antioxidant capacity.