Identification of Pyrogallol in the Ethyl Acetate-Soluble Part of Coffee as the Main Contributor to Its Xanthine Oxidase Inhibitory Activity.

In this study, ethyl acetate-soluble parts of hot-water extracts from roasted coffee beans were found to demonstrate potent xanthine oxidase (XO) inhibition. The XO inhibitory activities and chlorogenic lactone contents (chlorogenic lactones have previously been identified as XO inhibitors in roast coffee) were measured for ethyl acetate-soluble parts prepared from coffee beans roasted to three different degrees. Although chlorogenic lactone contents decreased with higher degrees of roasting, the XO inhibitory activity did not decrease. These data led us to investigate new potent inhibitors present in these ethyl acetate-soluble extracts. Repeated assay-guided purifications afforded a highly potent XO inhibitor, which was eluted before chlorogenic lactones via medium-pressure chromatography using an octadecylsilica gel column. The obtained inhibitor was identified as pyrogallol (1,2,3-trihydroxybenzene), which had an IC50 of 0.73 μmol L-1, much stronger than that of other related polyphenolic compounds. Quantitative analysis of pyrogallol and chlorogenic lactones revealed that pyrogallol (at concentrations of 33.9 ± 4.2 nmol mL-1 in light roast coffee and 39.4 ± 3.9 nmol mL-1 in dark roast coffee) was the main XO inhibitor in hot-water extracts of roasted coffee beans (i.e., drinking coffee).