Studies on the bioactivity of aqueous extract of pu-erh tea and its fractions: in vitro antioxidant activity and α-glycosidase inhibitory property, and their effect on postprandial hyperglycemia in diabetic mice.

Despite abundant research that has been carried out on the potential health benefits of pu-erh tea, no consensus till now, has been reached on which constituent is mainly responsible for its bioactivity. In this work, the aqueous extract (AE) and its fraction enriched with active constituents were prepared from pu-erh tea, and their bioactivities were investigated. It was found that tea polyphenols (TP), tea polysaccharides (TPS), caffeine (Caf), protein (Pro), amino acids (AA) were accumulated in several fractions after solvent extraction despite not being separated completely. Meanwhile, 95% ethanol precipitate (EP) and ethyl acetate fraction (EF) possessed remarkable antioxidant activity and potent inhibitory effects against α-glycosidase in vitro. Furthermore, all the extracts (50 mg/kg BW) showed a significant (p<0.05) effect on postprandial hyperglycemia in diabetic mice as compared with a model group, and the suppression of EP was not significantly (p>0.05) different from that of acarbose at the same dosage (50 mg/kg BW), which indicate that these fractions could be developed as potential anti-diabetic agents.