Abstract:
Tea is a popular beverage consumed worldwide. It is made by steeping the dried leaves, buds and twigs of Camella sinensis. This project sought to evaluate the antioxidant properties and the inhibitory effects of aqueous extracts of some commercial teas on the key enzymes linked with type 2 diabetes (α- amylase and α- glucosidase) - in vitro. The aqueous extracts of five commercial teas; Green tea, Lipton tea, Top tea, Master tea and Antidiabetes tea were prepared by extracting the teas in hot water (1: 100 w/v) and used for subsequent analysis. The total phenol, flavonoid and vitamin C contents were determined, the antioxidant properties as typified by their 1,1- diphenyl-2-picrylhydrazyl (DPPH), 2,21 azino-bis (3-ethylbenzthiazoline-6-sulphonic acid (ABTS) radical scavenging ability and ferric reducing antioxidant properties (FRAP) were evaluated. Thereafter, the ability of the tea extract to inhibit both FeSO4 and Sodium nitroprusside (SNP) - induced lipid peroxidation in rat pancreas were also determined. Then, the inhibitory effect of the teas on α-amylase and α-glucosidase activities was determined in vitro. The result of the study revealed that Green tea had the highest total phenol (9.50 mg/g), flavonoid (8.85 mg/g) content and antioxidant activities while Master tea [total phenol (4.7 mg/g), flavonoid (4.35 mg.g)] had the least. In addition, all the tea extracts inhibited some pro-oxidants (FeSO4 and SNP) induced lipid peroxidation in rat pancreas – in vitro, with Green tea having the highest inhibitory effect (except in SNP induced lipid peroxidation in rat pancreas). Furthermore, all the teas inhibited α-amylase and α-glucosidase activities in a dose-dependent manner. However, as revealed by their EC50 there was no significant (P > 0.05) difference in the α - amylase inhibitory activity of Master tea (1.16 mg/ml) and Antidiabetes tea (1.18 mg/ml) and also between Green tea (1.22 mg/ml) and Top tea (1.23 mg/ml), nevertheless, Lipton tea (1.27 mg/ml) had the least. Also, there was no significant (P > 0.05) difference in the α - glucosidase inhibitory activity among Green tea (1.12
mg/ml), Lipton tea (1.13 mg/ml), Master tea (1.13 mg/ml) and Top tea (1.13 mg/ml), nevertheless, Antidiabetes tea (1.16 mg/ml) had the least.
It could be concluded that the inhibition of key enzymes linked to type-2 diabetes (α – amylase and α – glucosidase) and prevention of lipid peroxidation in the pancreas could be some of the possible mechanism by which tea exert their anti-diabetes properties. However, Green tea had the highest antioxidant activity and was a better inhibitor of key enzymes linked to type-2 diabetes.
