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

A water soluble branched beta-D-glucan (PS-I) with an average molecular weight similar to 2.1 x 10(5) Da was isolated from alkaline extract of the fruit bodies of the edible mushroom Entoloma lividoalbum (Kuhner & Romagn) Kubicka which consists of terminal beta-D-glucopyranosyl, (1 -> 3)-beta-D-glucopyranosyl, (1 -> 6)-beta-D-glucopyranosyl, and (1 -> 3,6)-beta-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)-beta-D-glucopyranosyl residues, one of which was branched at O-3 position with the side chain consisting of three (1 -> 3)-beta-D-glucopyranosyl and a terminal beta-D-glucopyranosyl residues. Total antioxidant capacity of 1 mg PS-I was measured and found equivalent to 70 +/- 15 mu g of ascorbic acid. The PS-I was found to possess hydroxyl and superoxide radical-scavenging activities with EC50 values of 480 and 150 mu g/mL, respectively. The reducing power of PS-I was determined 0.5 at 480 mu g/mL. (C) 2013 Elsevier B.V. All rights reserved.