Abstract: Crude Cordyceps militaris polysaccharides obtained by ethanol precipitation were purified by sequential column chromatographies on DEAE-cellulose 52 and Sephadex G-100. Further, purified Cordyceps militaris polysaccharides were successfully modified by either sulfation, carboxymethylation or acetylation and their antioxidant activity and that of their modification products were comparatively assessed based on the ability to in vitro scavenge superoxide anion, hydroxyl and alkyl free radicals. Carboxymethylation showed the largest degree of substitution for Cordyceps militaris polysaccharides, followed by acetylation and sulfation. Three different modification products revealed different antioxidant activities. Sulfation and carboxymethylation could obviously increase the antioxidant activity of Cordyceps militaris polysaccharides and result in the highest increase of respectively 95.19% and 73.58% in the scavenging rate against alkyl radical, followed by hydroxyl and superoxide anion radicals. A decrease in the ability to scavenge superoxide anion, hydroxyl and alkyl free radical, however, was observed after acetylation. Therefore, the antioxidant activity of polysaccharides from Cordyceps militaris can be improved remarkably through appropriate chemical modifications.

Key words: Cordyceps militaris, polysaccharide, purification, chemical modification, anti-oxidation