Change of Polyphenol Oxidase Activity during Oolong Tea Process

It was believed that catechins produced theaflavins (TF) and low molecular weight, chromatographically resolved thearubigins (TR) in the presence of polyphenol oxidase (PPO). So, the changes of oolong tea PPO activity, tannin, TF, TR contents were considered. Green tea leaves were going through the stages: fresh tea → withering → fermentation → dried inactivated enzyme → final products. Tea samples in the stages were conducted. Enzyme PPO from tea samples was extracted by 0.1M phosphate buffer (pH 7.5), addition of 1% PEG (v/v). PPO activity was determined by a spectrophotometer at 420nm with pyrocatechol as standard. The results showed that the PPO activity increased from fresh tea leaves (100%) to the withering stage (111.89%), decreased steadily in the rolled 1 (96.83%). Then, the PPO activity fluctuated continuously, peaked at the incubated 2 and 3 and fell sharply after that. The enzyme activity in the final product was 7.95% compared with the fresh one. PPO activity had a positive influence on the TF/TR ratio and catechins depletion.