title: Evaluation of the in vitro α-glucosidase inhibitory activity of green tea polyphenols and different tea types.
abstract: BACKGROUND
  The objective of this study was to determine whether green tea, black tea and oolong tea have inhibitory potential against α-glucosidase which may be used to control postprandial hyperglycemia in type 2 diabetes mellitus.
  
  
  RESULTS
  Green tea polyphenols (TPs) strongly inhibited α-glucosidase activity by non-competitive inhibition with an IC50 value of 2.33 µg mL(-1) and the inhibitory effect was dependent on TP concentration and incubation order. Green tea, black tea and oolong tea also had dose-dependent inhibitory potential with IC50 values of 2.82, 2.25 and 1.38 µg mL(-1) (µg polyphenol mL(-1)), respectively. The study also showed that the content of unprecipitated TPs changed during enzymatic hydrolysis, leading to the change of the antioxidant activity. The change of the antioxidant activity of tea extracts revealed a similar trend to that of green TPs during enzymatic hydrolysis.
  
  
  CONCLUSIONS
  Green TPs, green tea, black tea and oolong tea are excellent α-glucosidase inhibitors and their inhibitory potency is mainly attributed to TPs. These findings suggest that green tea, black tea and oolong tea can potentially be used to control postprandial hyperglycemia.
authors.affiliation: Key Laboratory of Horticultural Plant Biology, Huazhong Agricultural University, Ministry of Education, Wuhan 430070, P.R. China.|Department of Food Science and Technology, College of Agricultural and Environmental Sciences, The University of Georgia, Athens, Georgia, USA.
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Yang
authors.affiliation: Department of Food Science and Technology, College of Agricultural and Environmental Sciences, The University of Georgia, Athens, Georgia, USA.
authors.forename: Fanbin
authors.initials: F
authors.lastname: Kong
mesh_terms: D000975:Antioxidants; D028241:Camellia sinensis / Q000737:chemistry; D011232:Chemical Precipitation; D003924:Diabetes Mellitus, Type 2 / Q000150:complications*; D065089:Glycoside Hydrolase Inhibitors / Q000494:pharmacology*; D006868:Hydrolysis; D006943:Hyperglycemia / Q000517:prevention & control*; D007004:Hypoglycemic Agents; D010936:Plant Extracts / Q000737:chemistry; D018515:Plant Leaves / Q000737:chemistry; D059808:Polyphenols / Q000032:analysis / Q000378:metabolism / Q000494:pharmacology*; D013662:Tea / Q000737:chemistry* / Q000145:classification
chemical_list: D000975:Antioxidants; D065089:Glycoside Hydrolase Inhibitors; D007004:Hypoglycemic Agents; D010936:Plant Extracts; D059808:Polyphenols; D013662:Tea
keywords: antioxidant capacity; enzyme inhibition; tea; tea polyphenols; α-glucosidase