Structural Characterization and Hypoglycemic Effect in Vitro of Phosphorylated Auricularia auriculata Polysaccharide

In this study, the Auricularia auriculata polysaccharides extracted using high pressure-shearing extraction method were phosphorylated at different temperatures using sodium trimetaphosphite as a crosslinking agent, and the structure and in vitro hypoglycemic activity of the modified polysaccharides were characterized. The results showed that the phosphorylated polysaccharides were heteropolysaccharides mainly composed of xylose, fructose, mannose and glucose. With the increase of temperature, the molecular mass of the phosphorylated polysaccharides decreased significantly and a triple-stranded helical structure was observed. Infrared (IR) spectra showed that the characteristic absorption peaks of P=O and P–O–C appeared at 1205 and 898 cm^-1. Nuclear magnetic resonance (NMR) spectra showed that the phosphorylation mainly occurred on the C6 hydroxyl groups, and the signal peak of P in the phosphate group appeared in the range of δ 0–1.5. Scanning electron microscopic (SEM) results showed that the surface morphology of the modified polysaccharides changed significantly, and it was finer and more broken compared to the original polysaccharides. In addition, 5.0 mg/mL of the phosphorylated polysaccharide PAAP-4 had strong inhibitory effect on α-glucosidase and α-amylase. The inhibitory rate of α-glucosidase was 56.89%, and the in vitro hypoglycemic activity was enhanced compared to that of the original polysaccharides.