Changes in enzyme activities in the tea plant (Camellia sinensis) according to withering time

Withering is the first step in tea processing and has a significant impact on the final product quality. During the withering of green tea leaves and their preparation for the subsequent processing step (rolling), the reduction in leaf moisture content is accompanied by biochemical interactions that play a critical role in determining product quality, particularly its aroma. One of the major biochemical events during withering is the change in enzyme activities. Enzymes in tea leaves contribute to the taste, aroma, and color of tea. The withering time of fresh leaves is an important factor affecting the consistency of tea flavor quality. However, the effects of different natural withering durations on the activity of alcohol dehydrogenase (ADH), peptidase, and polyphenol oxidase (PPO)—enzymes that play a critical role in determining tea quality characteristics such as aroma, taste, and colour—remain unclear. This study represents the first attempt to investigate the effects of different withering durations (0, 16, 17, 18, 19, 20, and 24 hours) on ADH, peptidase, and PPO activities in the Ali Rıza Erten and Zihni Derin tea clones, which were cultivated under controlled conditions in the tea nurseries of the Atatürk Tea and Horticultural Research Institute. The highest peptidase activity in both clones was observed in samples with 24 hours of withering, whereas the lowest activity was detected in the 17-hour withered sample of the Ali Rıza Erten clone and the 19-hour withered sample of the Zihni Derin clone. The highest ADH activity was observed at 18 hours for the Ali Rıza Erten clone and at 20 hours for the Zihni Derin clone. Conversely, the lowest ADH activities were recorded at 20 hours and 0 hours (control group) for the Ali Rıza Erten and Zihni Derin clones, respectively. For PPO, the highest enzyme activity was detected in the 16-hour (Ali Rıza Erten) and 18-hour (Zihni Derin) samples, while the lowest activity was found in the 0-hour (control) samples of both clones. Except for the highest peptidase activity observed at 24 hours, it was found that different withering durations affected the enzyme activities in both clones, with each duration exhibiting a distinct level of enzyme activity. When evaluating the enzyme activities of both clones overall, the highest ADH and PPO activities were detected in samples with 18 hours of withering, while the highest peptidase activity was observed in the 24-hour samples. The enzyme activities of the Zihni Derin clone were found to be higher than those of the Ali Rıza Erten clone. A weak and non-significant positive correlation was found between the clones and ADH activity, a moderate and significant positive correlation with peptidase activity, and a strong and highly significant positive correlation with PPO activity. These findings suggest that the relationships between ADH, PPO, and peptidase activities and the clones may reveal clonal differences in key tea quality traits such as aroma, taste, umami, and colour, thereby contributing to selection and the development of unique tea clones.