Extraction optimization of polysaccharides from Gougunao tea and assessment of the antioxidant and hypoglycemic activities of its fractions in vitro

The extraction optimization, characterization, antioxidant activities and hypoglycemic in vitro of polysaccharides from Gougunao tea (GTP) were investigated in this study. The extraction conditions were optimized as extraction time of 3.2 h, solid-liquid ratio of 1:30 (g/mL) and extraction temperature of 95 °C, reaching a maximum yield of 10.78 ± 0.21%. Three new fractions (GTP40, GTP60 and GTP80) were separated from GTP by gradient concentrations of ethanol. Their weight-average molecular weight, number-average molecular weight and polydispersity index were determined to be 48286–195451 Da, 33946–118948 Da, 1.422–1.643 by the high-performance gel permeation chromatography (HPGPC). Chemical analysis revealed that they were all composed of arabinose, galactose, ribose, glucose, rhamnose, manose, xylose, glucuronic acid, and galacturonic acid with different molar ratios, as well as a small amount of proteins. What's remarkable is that the antioxidant and hypoglycemic activities in vitro of them were all in the order of GTP40>GTP60>GTP80 in a concentration-dependent manner. The half inhibition concentrations (IC50) of GTP40 for 2,2-Diphenyl-1-picrylhydrazyl radical, 2,2'-Azino-bis (3-ethylbenzothiazoline- 6-sulfonic acid) radical, hydroxyl radical were 0.066 mg/mL, 0.255 mg/mL and 3.610 mg/mL, and for α-amylase and α-glucosidase were 1.271 mg/mL and 0.013 mg/mL, respectively. It will provide a theoretical basis for the further utilization of polysaccharides from Gougunao tea.