Tea (Camellia sinensis L.) is categorized into four types depending on the degree of fermentation, which in turn affects the physicochemical properties of tea. In this work, aqueous extracts of four typical teas, named green tea, oolong tea, black tea and puerh tea, were obtained, and their chemical compositions and bioactivities including antioxidant activity and inhibition on α-amylase and α-glycosidase were compared. It was found oolong and green tea not only possessed stronger antioxidant ability in assays of DPPH, ABTS and FRAP, but also had more power on inhibition on α-amylase and α-glycosidase. Pearson correlation analysis showed tea polyphenols and catechins had significant positive correlations on α-amylase inhibition. However, caffeine was observed to have a significant negative effect on α-glycosidase inhibition. These results indicated teas with no or slight fermentation (decaffeinated was better), were suitable for diabetes.
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