Structure elucidation and antioxidant properties of a soluble β-d-glucan from mushroom Entoloma lividoalbum

A water soluble branched β-d-glucan (PS-I) with an average molecular weight ∼2.1 × 105 Da was isolated from alkaline extract of the fruit bodies of the edible mushroom Entoloma lividoalbum (Kühner & Romagn) Kubička which consists of terminal β-d-glucopyranosyl, (1 → 3)-β-d-glucopyranosyl, (1 → 6)-β-d-glucopyranosyl, and (1 → 3,6)-β-d-glucopyranosyl moieties in a molar ratio of nearly 1:3:2:1. The structure of PS-I was elucidated using acid hydrolysis, methylation analysis, periodate oxidation study, partial hydrolysis, and 1D/2D NMR experiments. The repeating unit of the polysaccharide (PS-I) contains a backbone chain of three (1 → 6)-β-d-glucopyranosyl residues, one of which was branched at O-3 position with the side chain consisting of three (1 → 3)-β-d-glucopyranosyl and a terminal β-d-glucopyranosyl residues. Total antioxidant capacity of 1 mg PS-I was measured and found equivalent to 70 ± 15 μg of ascorbic acid. The PS-I was found to possess hydroxyl and superoxide radical-scavenging activities with EC50 values of 480 and 150 μg/mL, respectively. The reducing power of PS-I was determined 0.5 at 480 μg/mL.