Mechanistic insights into aroma differences of Taiping Kuihong black tea processed by different withering methods based on sensory directed analysis, metabolomics, and key enzyme activity assays

Withering is a critical process influencing the aroma formation of Taiping Kuihong Black Tea (TKBT). In this study, sensory directed analysis, targeted metabolomics, and key enzyme activity assays were employed to systematically compare the effects of hot-air withering (HW), mixed-mode withering (MW), and constant temperature and humidity withering (CTHW) on the aroma characteristics and their underlying formation mechanisms in TKBT. The results showed that HW exhibited stronger floral, fruity, sweet, and potato-like aroma, whereas CTHW was dominated by green aroma. Combined with gas chromatography-olfactometry, odor active value, aroma recombination, and aroma omission experiments, 9 key aroma-active compounds contributing to the characteristic aroma profile of the samples were further identified. Variations in these metabolites were mainly driven by heat-regulated enzyme activities and aroma precursors, leading to the redistribution of volatile compounds. This study provides a theoretical basis and technical support for improving the aroma quality of TKBT.