In vitro experiments were conducted to ascertain the inhibitory effects of various teas produced using different methods on sucrase activity. In addition, the suppressive effects of manufactured teas on hyperglycemia were ascertained by portal vein catheterization using rats. The respective efficacies of the various teas on inhibiting sucrase activity were the greatest in green tea, followed by oolong tea, pu-erh tea and black tea. The IC50 of each tea was 0.62, 1.03, 3.01 and 4.41, respectively. In rats with catheterized portal veins, green tea had the strongest suppressive effect on hyperglycemia, followed by oolong tea while black tea and pu-erh tea did not suppress hyperglycemia. Furthermore, in order to clarify the effects associated with different degrees of fermentation, green tea from Sri Lanka was oxidized using laccase. The results revealed that the prolong of the oxidation time decrease the suppressive effect on sucrase activity or hyperglycemia. Furthermore, even when microbial fermentation was performed as in the case of pu-erh tea, the suppressive effects of tea on sucrase activity or hyperglycemia were decreased. The differences in the efficacy of various teas with respect to suppressing hyperglycemia are thus due to the changes in tea polyphenol composition caused by fermentation.
