Abstract: The aim of this study was to evaluate the structural characteristics and anti-diabetic mechanism of tea polysaccharides, dietary ingredients used for the management of diabetes. A water-soluble polysaccharide was isolated and purified from mature tea leaves, and its monosaccharide composition and molecular mass were measured. Also, its structural characteristics were analyzed by ultraviolet (UV) and infrared (IR) spectroscopy were. Alloxan was injected into ICR mice to induce non-obese type diabetes. The diabetic rats were treated with the polysaccharide (100 mg/(kg·d)) or glibenclamide (positive control) for 42 days. The fasting blood glucose, serum insulin and total antioxidant parameters in serum and liver were determined. The pancreas was examined by haematoxylineosin staining and β-cells were observed using a microscope. The results showed that the molecular mass of the polysaccharide was 119 600 Da, which was composed of glucuronic acid, rhamnose, fucose, arabinose, xylose, mannose, glucose and galactose with a molar ratio of 32.61:1.00:5.46:8.13:3.84:2.37:15.36:7.52. Based on the UV and IR spectra, it seemed likely that the polysaccharide was a non-protein-bound pyran-type heteropolysaccharide. The treatment of the diabetic rats with the polysaccharide significantly elevated liver glycogen content, and decreased blood glucose to normal from 18.98 mmol/L, but exhibited no significant difference in pancreatic and plasma insulin levels compared with the normal group (P > 0.05). Moreover, treatment with the polysaccharide significantly increased superoxide dismutase activity compared with the model group (P < 0.05), but showed nitricoxide synthase activity and malonaldehyde content in liver close to those of the negative group; however, a significant decrease in nitric oxide in liver was found in comparison with the model group (P < 0.05). The effect of the polysaccharide was similar to that of glibenclamide. Histopathological and morphological results demonstrated that pancreatic β-cells and liver tissue morphology in the polysaccharide treated group were restored to normal. Thus, this study suggests that the tea polysaccharide exerts anti-diabetic effects by improving insulin secretion, β-cell function, and antioxidant status.

Key words: tea polysaccharides, structural characteristics, antioxidant activity, hypoglycemic activity, insulin secretion, β-cell function