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

The roasting process of pyrogallol, a polyphenol compound distributed in coffee beverages, significantly enhanced its α-glucosidase inhibitory activity. In this study, a bioassay-guided isolation of the thermal reaction products of pyrogallol led to the identification of two potent α-glucosidase inhibitors, 4-4′ dimer of pyrogallol (4,4′-DP) and 4-5′ dimer of pyrogallol (4,5′-DP). Their α-glucosidase inhibitory activity was higher than that of pyrogallol, as evidenced by comparing the IC50 values (206.2 ± 1.2 μM for 4,4′-DP, 187.6 ± 2.6 μM for 4,5′-DP, 2660 ± 60.1 μM for pyrogallol). And the roasting products were more potent α-glucosidase inhibitors compared to acarbose (IC50 = 695 ± 12.7 μM). Enzyme kinetics demonstrated that 4,4′-DP and 4,5′-DP inhibited α-glucosidase in an uncompetitive and a non-competitive manner, respectively. Docking simulations revealed that the main interaction forces between these two compounds and α-glucosidase were hydrogen bonding and hydrophobic effect. These results suggested that a simple roasting process might increase the α-glucosidase inhibitory activity of pyrogallol-containing foods such as coffee beverages.