In vitro Analysis on Inhibitory Activity of Amylolytic Enzymes in Decaffeinated Green Coffee Bean Extracts and Contributions of Chlorogenic Acids

Extract of decaffeinated green coffee beans (EDGCB) was prepared by supercritical CO2 treatment and alcohol extraction and contained 38% (w/w) chlorogenic acids (CQAs, consisting of 8 kinds of chlorogenic acid isomers). The effects of CQAs in EDGCB on inhibitory contribution of amylolytic enzymes (a-glucosidase and alpha-amylase) were examined in vitro. The activity of these amylolytic enzymes was inhibited depending on the EDGCB concentration. and CQAs significantly contributed by 63.1-85.8%. Comparison of CQA isomers showed that inhibitory activities of di-caffeoylquinic acids (3,5-diCQA, 3,4-diCQA and 4,5-diCQA) were the strongest, followed by those of caffeoylquinic acids (3-CQA, 5-CQA and 4-CQA) and feruloylquinic acids (5-FQA and 4-FQA) in alpha-amylase and sucrase. 3,4-diCQA was the main active component in EDGCB for inhibiting maltase. The number of caffeoyl groups and the binding position for quinic acid significantly affected the inhibitory activity of CQAs. The effects of EDGCB on the inhibitory activity of alpha-GI (acarbose or voglibose) in vitro and on the postprandial blood glucose level were next examined using rats. Addition of EDGCB to the reaction mixture with a low concentration of alpha-GI showed additive inhibitory effects of each enzyme. Moreover. EDGCB prevented the increase in blood glucose level in vivo. These results Suggest that EDGCB is useful for prevention of postprandial hyperglycemia.