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

[Display omitted] ► A heteroglycan was isolated from the mycelia of P. ostreatus. ► Its structure was determined by chemical as well as 2D NMR studies. ► This molecule showed antioxidant properties. 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 (1H, 13C, 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 βd-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 EC50 value of PS at 943μg/mL was determined. Further, EC50 value of the PS at 53μg/mL was observed for scavenging activity of superoxide free radicals. Chelating effects (54.82%) of ferrous ions were observed at 1mg/mL of the PS.