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

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.