Physicochemical analysis, structural elucidation and bioactivities of a high-molecular-weight polysaccharide from Phellinus igniarius mycelia

Phellinus igniarius is a well-known edible and medicinal fungus consumed in Asia for centuries. In the present study, a polysaccharide named PIP-1 was obtained from Phellinus igniarius mycelia, its physicochemical properties were determined, its detailed structures were elucidated by analysis of its depolymerized product, and its antioxidant and antitumor activities were evaluated. Results showed that PIP-1 had a high molecular weight, a high intrinsic viscosity and a linear repeating backbone composed of glucopyranose (Glcp), galactopyranose, and mannopyranose joined by α-(1 → 4), α-(1 → 3), and α-(1 → 6) linkages, and single α‑terminal‑D‑Glcp as side chains 6-O-linked to the main chain according to the GC-MS and NMR results, and exhibited triple helical structure. Pharmacological results revealed that PIP-1 could effectively scavenge hydroxyl radicals, partly scavenge DPPH radials and chelate ferrous metal ions. Furthermore, PIP-1 showed potent inhibitory effects on growth of HT-29 and MCF-7 cells. These findings suggested that high-molecular-weight PIP-1 containing triple helical structure and only α-type glycosidic bond holds promise as novel functional foods and agents to promote human health.