Molecular properties and antioxidant activities of polysaccharides isolated from alkaline extract of wild Armillaria ostoyae mushrooms

Abstract

This study aims to discover novel and bioactive polysaccharides (PS) from wild Armillaria ostoyae, a honey mushroom species. Two PS designated AkPS1V-1 (66.6 kDa) and AkPS1V-2 (15.3 kDa) were isolated and fractionated by anion ion exchange (IEC) and size exclusion chromatography (SEC) from the alkaline extract of A. ostoyae mushrooms. AkPS1V-1 was a glucan composed of solely glucose residues and AkPS1V-2 a heteropolysaccharide composed of glucose and galactose at 6:1 molar ratio. AkPS1V-2 exhibited higher antioxidant activities than AkPS1V-1 based on reducing power, radical scavenging and metal chelating assays. The structure of AkPS1V-2 was further analyzed and elucidated as a branched galactoglucan with a backbone composed of (1→6)-β-d-glucopyranosyl, (1→3)-β-d-glucopyranosyl, (1→3)-α-d-galactopyranosyl and (1→3,6)-β-d-glucopyranosyl residues at 3:1:1:1 ratio, and side chain of (1→3)-β-d-glucopyranosyl residue. This is the first report on a pure PS structure and its antioxidant activities from this mushroom species.