Discovery of pyrogallol thermal reaction products from a model process of roasting coffee beans as potentα-glucosidase inhibitors

The roasting process of pyrogallol,a polyphenol compound distributed in coffee beverages,significantly enhanced itsα-glucosidase inhibitory activity.In this study,a bioassay-guided isolation of the thermal reaction products of pyrogallol led to the identification of two potentα-glucosidase inhibitors,4-4′dimer of pyrogallol(4,4′-DP)and 4-5′dimer of pyrogallol(4,5′-DP).Theirα-glucosidase inhibitory activity was higher than that of pyrogallol,as evidenced by comparing the IC_(50)values(206.2±1.2μM for 4,4′-DP,187.6±2.6μM for 4,5′-DP,2660±60.1μM for pyrogallol).And the roasting products were more potentα-glucosidase inhibitors compared to acarbose(IC_(50)=695±12.7μM).Enzyme kinetics demonstrated that 4,4′-DP and 4,5′-DP inhibitedα-glucosidase in an uncompetitive and a non-competitive manner,respectively.Docking simulations revealed that the main interaction forces between these two compounds andα-glucosidase were hydrogen bonding and hydrophobic effect.These results suggested that a simple roasting process might increase theα-glucosidase inhibitory activity of pyrogallol-containing foods such as coffee beverages.