Abstract: In this paper, Liquid submerged fermentation technology was used to produce extracellular polysaccharide by using Fructificatio amaurodermatis Rudae strains. On the basis of single factor test, sucrose, yeast powder and fermentation time were used as impact factors, polysaccharide yield was used as response value, and extracellular polysaccharide fermentation was optimized by response surface analysis. The results showed that the optimal fermentation condition of F. amaurodermatis Rudae were as follows: sucrose 20.6 g·L^-1, yeast powder 11.2 g·L^-1 and fermentation time 6 d. In this fermentation condition, the theoretical content of extracellular polysaccharide was 237.35 mg·L^-1, and the actual value was 236.83 mg·L^-1, which was agreed with the theoretical value. Extracellular polysaccharide had strong inhibitory effect on DPPH radical and hydroxyl radical, and its inhibitory effect became stronger with the increase of polysaccharide concentration. This study provided a theoretical basis for the comprehensive development and utilization of extracellular polysaccharide produced by liquid fermentation.

Key words: Fructificatio amaurodermatis Rudae, liquid submerged fermentation, extracellular polysaccharide, response surface methodology