Abstract: The in vitro antioxidant activities of water-extracted mycelial polysaccharide (WPS),sodium hydroxide-extracted mycelial polysaccharide (SPS) and exopolysaccharide (EPS) from rice false smut pathogen Villosiclava virens UV-2 were evaluated using Fe³⁺ reducing activity and ·OH radical scavenging activity assays.EPS exhibited the strongest antioxidant activity among the polysaccharides.In order to increase EPS yield in fermentation culture of V.virens, the main effective factors on EPS production,namely concentrations of glucose and peptone,in fermentation culture were screened by Plackett-Burman experimental matrix.The optimal concentration ranges of glucose and peptone were respectively determined as 70-90 g/L and 10-20 g/L by the single-factor experiments.Both the central composite design and response surface methodology were employed to optimize the tested variables (concentrations of glucose and peptone) and to establish a second-order polynomial regression equation between EPS yield and the variables.When the concentrations of glucose and peptone in medium were at 84.08 g/L and 14.11 g/L,respectively,the EPS yield reached the maximum (881.40 mg/L).Verification experiment confirmed the validity with the actual EPS yield as 917.80 mg/L,which was 10.55-fold in comparison with that (87.00 mg/L) in the original basal medium.The results provided supporting data for EPS production in large scale and also speeded up the application of the fungus V.virens.

Key words: Villosiclava virens, water-extracted mycelial polysaccharide, sodium hydroxide-extracted mycelial polysaccharide, exopolysaccharide, antioxidant activity, medium optimization