Structure elucidation and antioxidant activity of a novel polysaccharide from Polyporus umbellatus sclerotia

A novel water-soluble polysaccharide PUP60S2, with a molecular weight of 1.44 × 104 Da, was obtained from the sclerotia of Polyporus umbellatus by hot water extraction, ethanol precipitation, anion-exchange and size-exclusion chromatography. PUP60S2 was a polysaccharide comprised of about 22.3% glucuronic acid. Monosaccharide composition analysis showed that PUP60S2 was only comprised of glucose and glucuronic acid. Reduction of carboxyl groups, sugar analysis, methylation analysis, together with one and two dimension NMR spectra disclosed that the backbone of PUP60S2 consisted of (1 → 6)-β-d-glucopyranosyl, every second of which was substituted at O-3 by side chains consisting of terminal β-d-Glcp, (1 → 3)-β-d-Glcp, (1 → 3)-β-d-GlcpA, (1 → 4)-β-d-Glcp and (1 → 4)-β-d-GlcpA units. The antioxidant activity assay in vitro showed that PUP60S2 exerted a significant scavenging effect on DPPH, hydroxyl radical and superoxide radical in a dose-dependent manner.