Structural characterization and antioxidant activity of a heteropolysaccharide from Ganoderma capense

•A novel polysaccharide (GCPB-3) was isolated from mycelia of Ganoderma capense (Lloyd) Teng.•The relative molecular weight is 124kDa and a specific optical rotation is [α]D25=+145°.•GCPB-3 is a heteropolysaccharide with backbone consisting of β-l-Arap and β-d-Xylp, linked with 1→4 sugar bonds.•GCPB-3 has a certain activity of DPPH•- and hydroxy-radical scavenging. In this work, crude polysaccharide extracts were obtained from mycelia of the edible fungus Ganoderma capense (Lloyd) Teng. After removal of proteins by the Sevage method, fractionation and purification by anion-exchange and gel-permeation chromatography, a polysaccharide (GCPB-3) was isolated. The relative molecular weight of GCPB-3 was 124kDa determined by high performance gel permeation chromatography (HPGPC). The homogeneous polysaccharide was composed of d-xylose and l-arabinose in the ratio of 1:1, and showed a specific optical rotation of [α]D25=+145°(c 1.0, H2O). Its structural features were determined by monosaccharide analysis, partial acid hydrolysis, methylation analysis, periodic acid oxidation, gas chromatography-mass spectrometry (GC-MS), Fourier transform-infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy (1H, 13C, HMQC and HMBC). The results characterized GCPB-3 as a heteropolysaccharide with backbone consisting of β-l-Arap and β-d-Xylp, linked with 1→4 sugar bonds. Interestingly, GCPB-3 showed some DPPH•- and hydroxy-radical scavenging activities.