Key sweet-aroma compounds and formation mechanisms in Mengding bud yellow tea using HS-SPME-GC-MS and sensomics

Mengding Bud Yellow Tea (MDBYT) is distinguished by its characteristic sweet and umami aroma. This study integrated quantitative descriptive analysis, HS-SPME-GC-MS, and UPLC-QQQ-MS to systematically elucidate, for the first time, the dynamic evolution of MDBYT aroma and its formation mechanisms. Sensory evaluation revealed that, among the 13 aroma descriptors, sweetness, umami, and mellowness were the primary attributes positively correlated with overall aroma quality. The yellowing process was the pivotal stage driving the aroma transition from grassy to sweet and umami notes. A total of 38 differential metabolites were identified, of which β-ionone, linalool, n-pentanal, n-heptanal, n-octanal, and 1-octen-3-ol, emerged as key contributors. These metabolites were primarily involved in modulating the sweetness, umami, and mellowness attributes of MDBYT. Quantitative profiling of 10 classes of GBVs demonstrated significant accumulation of linalyl and geranyl glycosides during the fixing and yellowing stages, providing strong evidence that glycoside hydrolysis constitutes a major release pathway for aroma-active compounds. Collectively, these findings demonstrate that the unique aroma of MDBYT is established through a coordinated, processing-driven biochemical network involving carotenoid degradation, glycoside hydrolysis, and lipid oxidation. This study provides a robust scientific foundation for the targeted regulation of flavor quality and the optimization of yellow tea processing strategies.