Study on Aroma Formation During the Withering Period of Ningchow Black Tea

Withering is the first process in black tea production, during which volatile compounds undergo complex enzymatic transformations that significantly influence the aroma profile of the tea. Herein, this study investigated the change trends of volatile compounds and corresponding enzymes throughout the withering period of Ningchow black tea. Sensory evaluation showed that withering enhanced the aroma quality of the tea leaves. A total of 165 volatile compounds were identified using gas chromatography-mass spectrometry. After withering, the flavor index displayed a significant decrease. Among the 100 differential volatile compounds (p < 0.01), the top up-regulated volatiles were primarily fatty acid-derived volatiles, while the top down-regulated volatiles originated from diverse precursors. The contents of most fatty acid-, amino acid-, and carotenoid-derived alcohols and aldehydes were significantly increased, while most volatile terpenoids and other volatiles showed opposite change trends. Consistent with these changes, the activities and protein levels of key enzymes largely paralleled the alterations in volatile compounds. This study provides a detailed characterization of the formation of volatile components during the withering stage of Ningchow black tea production.