Valorization of tea stems: Dynamic changes in volatile and non-volatile components via Tencha processing

Discarded tea stems possess unique flavor profiles yet remain an underutilized resource. This study aimed to evaluate their potential by investigating the dynamic changes in sensory constituents during processing on a tencha production line. Using non-targeted metabolomics and sensomics (QDA, GC–MS, LC-MS, and aroma recombination/omission experiments), we analyzed the chemical and sensory profiles. Processed stems exhibited enhanced umami and sweetness with reduced bitterness compared to leaves. Among 1440 non-volatiles, catechins and caffeine decreased significantly, whereas specific flavonoids, dipeptides, and glycosylated derivatives increased. We identified 243 volatiles, dominated by terpenoids. Although total volatile content declined during processing, heterocyclic compounds increased, and several key volatiles—including damascenone, cedrol, and 1-(2-furanyl)-1-pentanone—either increased markedly or newly appeared. Aroma recombination and omission tests confirmed 11 key volatiles as essential contributors to the characteristic aroma of processed stems. Overall, these findings highlight the potential of tea stems as a novel raw material for developing substantial tea-based products.