Roasting Enhances Xanthine Oxidase Inhibition of Green Tea: Chemical Evidence from Inhibitor Identification

Abstract

In this study, the effects of roasting on the xanthine oxidase (XO) inhibitory activity of green tea were investigated based on chemical analysis. It was found that XO inhibitory activity increased with roasting temperature, reaching a maximum of 91% inhibition at 200 °C, before declining at higher temperatures. High-performance liquid chromatography (HPLC) analysis revealed that major tea catechins, such as epigallocatechin gallate (EGCG), were eliminated upon roasting at 200 °C, while flavonols (myricetin, quercetin, and kaempferol) formed and exhibited strong XO inhibitory activity. A newly defined activity-contributing value (ACV) analysis indicated that these flavonols became the primary contributors to XO inhibition in roasted tea among the compounds identified by HPLC. Additionally, pyrogallol, likely generated from EGCG during roasting, was identified as another potent inhibitor with a high ACV. These results demonstrate that controlled roasting at approximately 200 °C enhances the XO inhibitory activity of green tea through the formation of flavonols and pyrogallol.