Sulfation of the extracellular polysaccharide from the edible fungus Stropharia rugosoannulata with its antioxidant activity
Hui Hao, Chun Cui, Yuqing Xing, Xuewei Jia, Bingjie Ma, Wenyi Kang, Tianxiao Li, Mingqi Gao, Chunping Xu
Abstract
An acidic extracellular polysaccharide (EPS) was gained from Stropharia rugosoannulata fermentation broth by the alcohol precipitate method. Sulfated derivative of EPS (S-EPS) was gained by chlorosulfonic acid-pyridine method and the conditions were as follows: pyridine as the reaction solvent, temperature 80 °C, and reaction time 90 min. The chemical structure and chain conformation of EPS and S-EPS were characterized by FT-IR, NMR and size exclusion chromatography (SEC) coupled with multi-angle laser light scattering (MALLS) detection. FT-IR spectra indicated the sulfated group was linked to the polymer. The EPS mainly consists of mannose, glucose and glucuronic acid, and the glycosidic bond type is mainly (1→4)-linked and (1→6)-linked. C6 and C2 were substituted by sulfate groups. The EPS was degraded into smaller molecular weight (Mw) polysaccharides with the larger molecular size (Rg) after sulfation and S-EPS has better hydrophilicity. Moreover, the sulfated derivative S-EPS was found to have a better scavenging ability on hydroxyl radicals than EPS. It proved that the chemical modification of S. rugosoannulata polysaccharides by sulfation effectively enhanced their antioxidant activity.