Effects of dynamic and static withering technology on volatile and nonvolatile components of Keemun black tea using GC-MS and HPLC combined with chemometrics

Withering process is one of the most crucial steps in Keemun black tea (KBT) manufacturing, which is the foundation of quality formation. This study investigated the effects of conventional static withering and innovative dynamic withering on the volatile and nonvolatile compounds of KBT. Overall, 79 volatile compounds were identified in five tea samples (FL: fresh leaf for control; SW7h, SW15h: leaves of static withering 7 h and 15 h; and DW7h, DW15h: leaves of dynamic withering 7 h and 15 h) by using HS-SPME/GC-MS. Orthogonal projections to latent structures discriminant analysis (OPLS-DA) were used to classify samples, and 36 key markers in volatile compounds were selected. Quantitative descriptive analysis (QDA) of KBT aroma showed that in dynamic withering, dense, floral and fruity aroma were significantly improved. The 14 odor-active compounds were speculated as the cause of QDA differences in aroma between dynamic and static withering. Meanwhile, theaflavins were generated and accumulated earlier in dynamic withering. Notably, the contents of aspartic acid, serine, glycine, arginine, cysteine, methionine, lysine, isoleucine, and leucine significantly increased after dynamic withering. Our study provides a comparative investigation metabolite of dynamic and static withering processes, offering innovative dynamic withering methods to improve the quality of KBT.