Optimizing Culture Medium and Antioxidant Activity of Extracellular Polysaccharides in Liquid Fermentation of Flammulina velutipes

A response surface experiment was conducted to optimize the fermentation of Flammulina velutipes for the extracellular polysaccharides (EPS). Liquid media with varied amounts of glucose, peptone, KH₂PO₄, fruit and vegetable juices were used for the experimentation. At end of the process, the antioxidant activity of EPS in each liquid suspension was determined as the criterion for optimization. The results showed that (a) the effect of ingredients in medium on the antioxidant activity ranked as peptone > KH₂PO₄ > fruit/vegetable juices > glucose; (b) the medium containing 2.46% glucose, 0.5% peptone, 0.1% KH₂PO₄ and 15% fruit/vegetable juices produced the highest EPS in the suspension at 0.83 mg·mL^-1; (c) at concentrations exceeding 2 mg·mL^-1, EPS obtained from the fermentation exhibited a strong scavenging effect on DPPH and ABTS free radicals; (d) at a same concentration level, EPS had a greater DPPH free radical scavenging rate than Vc; and, (e) at concentrations higher than 1.5 mg·mL^-1, EPS exhibited a scavenging rate on ABTS free radicals similar to Vc, reaching 99.87%.