Physicochemical characterization of a high molecular weight bioactive β-d-glucan from the fruiting bodies of Ganoderma lucidum

A purified polysaccharide coded as GLP20 was obtained by precipitating a hot-water extract from Ganoderma lucidum fruiting bodies with 20% (V/V) ethanol. Its total carbohydrate content was 95.9%. Structural analysis showed that GLP20 was a β-(1 → 3)-linked d-glucan with a (1 → 6)-β-d-glucopyranosyl side-branching unit on every third residue. Cell culture study revealed that GLP20 can significantly increase NO production of RAW264.7 macrophages. The analysis of light scattering and high performance size exclusion chromatography (HPSEC) showed that the molecular weight and polydispersity of GLP20 was 3.75 × 106 Da and 1.36, respectively. GLP20 had a rigid chain conformation in aqueous solution. A conformation transition occurred in the alkaline solution with NaOH concentration larger than 0.15 M. The transition from ordered structure to single chain happened when GLP20 was heated above 135 °C in water solution and was irreversible as demonstrated by differential scanning calorimetry (DSC). GLP20 existed as random coils in DMSO.