Hypoglycemic Effect And Antioxidant Activity Of The Isolated Polysaccharides From Puerh Tea

In this study, the physicochemical characterization such as chemical composition, monosaccharide, molecular weight and IR spectral of three Puerh tea polysaccharides (PTPS-1, PTPS-3, PTPS-5) isolated from Puerh tea with aging time for one year, three years and five years were determined. In vitro antioxidant activities and their inhibitory effects on a-glucosidase were investigated. And the effects of Puerh tea polysaccharides lowering blood glucose levels and enhancing the antioxidant status in alloxan-induced diabetic mice were carried out.The experimental results were as follows:1. The content and chemical composition of Puerh tea polysaccharide were correlated with the aging time.It can be observed that the yields (0.79%for PTPS-1,2.24%for PTPS-3and3.66%for PTPS-5) and protein content of the PTPS significantly (p<0.05) increased with increasing aging time of the puerh teas. Meanwhile, the uronic acid contents in PTPS-5and PTPS-3were significantly (p<0.05) higher than that in PTPS-1, but there was no significant difference between that in PTPS-3and that in PTPS-5. According to the results of GC analysis, all PTPS were composed of seven monosaccharides which were L-rhamnose, D-fucose, L-arabinose, D-xylose, D-mannose, D-glucose and D-galactose, with the different molar ratios. The molecular weight determination demonstrated that increasing aging time of puerh teas would elevate the contents of low MW polysaccharides.2. Puerh tea polysaccharides showed strong antioxidant activity and prominent α-glucosidase inhibitory ability, and closely related with the aging time. In different methods (DPPH, ABTS and FRAP scavenging effects and Ferrous chelating ability), PTPS-5showed the best ABTS radical scavenging ability(IC50=0.49mg/ml), DPPH radical scavenging ability(IC5o=1.45mg/ml), Ferric-reducing antioxidant power ability (the value of FRAP was1623.07μmol/L, under concentration of1mg/ml), and ferrous ion chelating ability (IC50=0.73mg/ml), but exited lower antioxidant activity than BHT by ABTS, DPPH and FRAP assays and EDTA by FIC assay. It was interesting to note that PTPS-5(IC50=0.063mg/ml) inhibited α-glycosidase more potent than acarbose (IC50=0.18mg/ml). In addition, PTPS-3(IC50=0.18mg/ml) also exhibited a promising inhibitory effect on a-glycosid ase as potent as acarbose. However, PTPS-1showed the weakest inhibitory effect among the PTPS tested. The results above showed that the aging process markedly improved the antioxidant and a-glycosidase inhibitory activities of the isolated PTPS (PTPS-5> PTPS-3> PTPS-1).3. Puerh tea polysaccharides demonstrated positive effect on lowering the blood glucose and improve the symptoms of diabetic. PTPS-5(AUC=2085mmol.min/L) showed the best effect on postprandial hyperglycemia in diabetic mice, and2172mmol.min/L for PTPS-3and2246mmol.min/L for PTPS-1. Meanwhile, daily administration of PTPS (40mg/kg BW) could significantly lower the BG levels, which was not different (p<0.05) from the effects of metformin (15mg/kg BW) throughout the entire experiment.4. Puerh tea polysaccharides can effectively regulate the antioxidant status. After4-week administration of PTPS (40mg/kg BW), the SOD activity and MDA contents both in serum and liver were improved to the levels of those in normal mice. In regards to the serum GSH-Px activity, it was even significantly higher (p<0.05) than that in normal mice, indicating the oxidative stress induced by alloxan could be reversed by administration of PTPS.