Study on antioxidant and in vitro hypoglycemia activities of dark tea prepared from Camellia sinensis var. Baiye Dancong

The antioxidant activity and in vitro hypoglycemia activity of ethanol extract of dark tea prepared from Camellia sinensis var. Baiye Dancong and its different solvent extracts were assayed by DPPH method, FRAP method and α-pancreatic amylase inhibitory assay, α-glucosidase inhibitory assay, respectively. The results showed that the contents of both total flavonoids and total phenolics in the ethyl acetate extract were highest among the different solvent extracts, and had (155.68±4.34) mg/g of total flavonoids (calculated as rutin equivalent) and (313.84±9.79) mg/g of total phenolics (calculated as gallic acid equivalent) , respectively. The ethyl acetate extract achieved the strongest antioxidant activity, and its EC50 of DPPH· assay was 13.72μg/mL while the EC1 of FRAP capacity was 43.38μg/mL. The ethyl acetate extract of dark tea also showed significant α-pancreatic amylase and α-glucosidase inhibitory activities, achieved 95.83% inhibition on α-pancreatic amylase at the concentration of 5mg/mL while 91.30% inhibition on α-glucosidase at the concentration of 50μg/mL. Using HPLC-DAD-MS/MS analysis, twelve compounds in the ethyl acetate extract were identified by comparing their ultraviolet absorption spectra and mass spectra with those of the standards and data in the literatures. Several flavone glycosides with apigenin and keampferol as the aglycone moieties were detected besides tea alkaloids.