A heteroglycan from the mycelia of Pleurotus ostreatus: structure determination and study of antioxidant properties

Abstract A heteroglycan (PS) isolated from the mycelia of Pleurotus ostreatus was found to consist of l -fucose, d -mannose, and d -glucose in a molar ratio of nearly 1:2:3. On the basis of acid hydrolysis, methylation analysis, periodate oxidation, and NMR studies ( 1 H, 13 C, TOCSY, DQF-COSY, NOESY, ROESY, HSQC, HMBC, and DEPT), the structure of the repeating unit of the PS was determined. The repeating unit had a branched backbone composed of (1→6)-linked α and β d -glucose and (1→2)–linked α- l -fucose. Branching occurred at C-4 position of (1→6)-linked α- d -glucopyranosyl residue with terminal β- d -mannose and C-3 position of (1→6)-linked β- d -glucopyranosyl residue with (1→6)-α- d -mannopyranosyl moiety terminated by α- d -glucose. The structure of the repeating unit of the PS was proposed as: The antioxidant properties of the PS were studied. The scavenging activity of hydroxyl free radicals whose EC 50 value of PS at 943 μg/mL was determined. Further, EC 50 value of the PS at 53 μg/mL was observed for scavenging activity of superoxide free radicals. Chelating effects (54.82%) of ferrous ions were observed at 1 mg/mL of the PS.