Improving summer black tea quality via vibratory withering and piling fermentation: Insights from metabolomics and...

Summer black tea typically lacks the floral-fruity aroma and high catechin oligomer content of premium black tea, limiting consumer acceptance and resource utilization. We aimed to enhance the aroma and taste quality of summer black tea by introducing vibratory withering (VW), piling fermentation (PF), and their combination process (CP) into traditional processing (CK). Traditional (CK), VW, PF, and CP treatments were compared using sensory evaluation, physicochemical analysis, and integrated LC-MS, untargeted metabolomics, and HS-SPME/GC-MS volatile profiling. Our results demonstrated that CP considerably improved sensory quality, elevating theaflavins, theasinensins, and floral/fruity volatiles (e.g., geraniol, linalool, geranylacetone, β-ionone, α-ionone, nonanal, and trans-linalool oxide (furanoid), hexanal, 1-nonanol, citral, and benzaldehyde). VW activated the jasmonic acid pathway, promoting terpene biosynthesis and catechin oxidation, while PF enhanced carotenoid degradation and LOX pathway activity. The CP process improved the quality and levels of bioactive compounds in summer black tea, enhancing its sensory appeal and commercial value.