Optimization of Fermentation Process for Water-soluble Polysaccharides and Antioxidant Activity of Polygonatum odoratum Fermentated by Bacillus subtilis LY-05

To investigate the optimal process conditions for the production of water-soluble polysaccharides from Polygonatum odoratum by aprobiotics and compare the change of antioxidant activities of polysaccharides fermented and unfermented. In this study, Bacillus subtilis LY-05 was used as fermentation strain, and increasing rate of water-soluble polysaccharides was index. Seven factors including Polygonatum odoratum addition, nitrogen source, inorganic salt, inoculation amount, temperature, stirring speed and fermentation time were studied with the increasing rate of water-soluble polysaccharides. On the basis of single-factor experiment, the fermentation conditions were optimized with response surface method; and evaluating the changes of the DPPH·scavenging rate, ABTS+·scavenging rate, OH· scavenging rate and total reducing power in the antioxidant activity of Polygonatum odoratum polysaccharides fermented and unfermented. The results showed that optimal fermentation condition was as follows: Polygonatum odoratum addition 4%, yeast extract powder 3%, NaCl 1%, inoculation amount 3%, fermention temperature 35 ℃, stirrig speed 160 r/min, fermentation time 48 h. Under these conditions, the polysaccharide content reached 7.83 mg/mL, which was 71.78% higher than that before fermentation(4.56 mg/mL). The antioxidant experiment showed that the DPPH·, ABTS+·, OH· scavenging rate and total reducing power of the fermented polysaccharide increased at certain concentrations and showed polysaccharide concentration dependence. The semi-inhibitory concentration (IC50) of the fermented polysaccharide POP2 on ABTS+·radical scavenging was 2.21 mg/mL, and the semi-inhibitory concentration on OH·radical scavenging was 0.49 mg/mL. These results implied that fermentation with Bacillus subtilis could significantly improve the extraction efficiency of Polygonatum odoratum polysaccharides, and polysaccharides in fermentated Polygonatum odoratum had better antioxidant capacity.