Antioxidant and immunostimulant β-glucan from edible mushroom Russula albonigra (Krombh.) Fr.

A water soluble beta-glucan (PS) with an average molecular weight similar to 1.95 x 10(5) Da was isolated from the alkaline extract of ectomycorrhizal edible mushroom, Russula albonigra (Krombh.) Fr. and found to consist of terminal, (1 -> 3)-, (1 -> 6)-, and (1 -> 3,6)-linked beta-D-glucopyranosyl moieties in a ratio of nearly 1:2:2:1. The structure of this PS was elucidated on the basis of total hydrolysis, methylation analysis, Smith degradation, partial hydrolysis, and 1D/2D NMR experiments. On the basis of these experiments, the repeating unit of the PS was found to contain a backbone of three (1 -> 6)-beta-D-glucopyranosyl residues, one of which was branched at O-3 position with the side chain consisting of two (1 -> 3)-beta-D-glucopyranosyl and a terminal beta-D-glucopyranosyl residue. This PS showed in vitro macrophage activation by NO production as well as splenocytes and thymocytes proliferation. Moreover, it also exhibited potent antioxidant activities. (C) 2013 Elsevier Ltd. All rights reserved.