Changes in catechin content and superoxide anion scavenging activity of Goishi tea [Camellia sinensis] during manufacturing

Goishi tea, a post-heating fermented tea, is produced in Otoyo town in Kochi Prefecture, Japan. Two natural fermentation steps by aerobic and anaerobic fungi and microorganisms participate in the production of Goishi tea. To investigate the effects of the manufacturing process on the functionality of Goishi tea, changes in superoxide anion scavenging activity and catechin content in hot water extracts of Goishi tea were examined. Superoxide anion scavenging activity and catechin content drastically changed in the two fermentation steps. In addition, high levels of (-)-catechin and (-)-gallocatechine were observed in the final product of Goishi tea. However, the contribution of catechin and gallic acid determined in this study to the superoxide anion scavenging activity of Goishi tea was low. These results suggest that some other component generated during the two steps of fermentation is the main contributor to the superoxide anion scavenging activity of Goishi tea.