GABA-enriched old Oolong tea fermentation

Abstract

Oolong tea, being a semi-fermented variety, holds significance in the tea production industry. However, an important portion of stocked Oolong tea (old Oolong tea) was discarded from the market. Oolong GABA tea, known for its potential health benefits, can be produced through fermentation under oxygen-depleted conditions. Therefore, improving old tea into GABA-rich tea will contribute to limiting the discard of old tea from the market. In this study, old Oolong tea underwent fermentation at temperatures of 30ºC, 35ºC, and 40ºC for a duration of 48 hours. Key parameters, including GABA, tannins, total polyphenols, TF/TR ratio, and tea color, were monitored at six-hour intervals over the 48-hour fermentation period. The findings revealed that optimal conditions to produce high GABA content in old Oolong tea were identified at 35ºC for 42 hours, resulting in a GABA content of 121.2 mg/kg, which was five times higher than the control, accompanied by a clear and standard color characteristic of fermented tea. This underscores the importance of controlled fermentation conditions for enhancing the quality of GABA-enriched old Oolong tea.