Elucidation of Antioxidant Compounds in Goishi Tea

Abstract

　Goishi tea, a post-fermented tea, is produced in Otoyo town in Kochi Prefecture, Japan. It is produced by two-step aerobic-anaerobic fermentation process. In this study, we attempted to elucidate the major antioxidant compounds in Goishi tea. Liquid-liquid partitioning and various types of column chromatography were used to obtain the unknown antioxidant compounds in Goishi tea. Subsequently, pyrogallol and t-3, t-4-dihydroxycyclohexane-r-1-carboxylic acid were newly identified as antioxidant compounds by using IR, LC-MS, and NMR analyses. The pyrogallol content in Goishi tea was 11.9mg/g dry weight and its contribution to the O₂^- scavenging activity of Goishi tea was 28.2%. From these results, pyrogallol was determined to be one of the main antioxidant compounds in Goishi tea. Additionally, the change in pyrogallol content during Goishi tea production was investigated. The pyrogallol content increased during steaming and aerobic fermentation (days 1-5), then gradually decreased during the final stage of aerobic fermentation (day 6), anaerobic fermentation, and sun-drying; indicating that pyrogallol was formed mainly during aerobic fermentation. In the future, we intend to investigate the relationship between pyrogallol and the reported food functionalities of Goishi tea, such as its inhibitory effects on hypercholesterolemia, atherosclerosis, and diet-induced obesity.