Study on bitterness reduction and aroma enrichment of Kejia green tea based on storage duration through UPLC-MS/GC–MS technology

Kejia Green Tea (KJGT) exhibits particularly noticeable alterations in bitterness, astringency, and aroma during storage. However, the comprehensive metabolic mechanisms driving this evolution remain poorly understood. This study investigated the dynamic changes of flavor-related metabolites in KJGT during storage using UPLC-MS/GC–MS. Results demonstrated that storage significantly reduced bitter/astringent compounds (e.g., 5-hydroxymethylfurfural, proanthocyanidin B2) by modulating linoleic acid metabolism and quercetin glycoside biosynthesis. Concurrently, the roasted high-fire aroma significantly diminished (e.g., 2-ethoxy-3-methylpyrazine, 2-ethylbenzaldehyde-volatile) during storage, while nutty and woody undertones intensified, which significantly enhanced the tea's aroma. Notably, KJGT-10 exhibited the least bitterness and a more pleasant aroma compared to the other vintages. The study revealed the key material conversions and metabolic mechanisms in KJGT during storage, demonstrating that an appropriate storage duration markedly improved its flavor characteristics. It provided a theoretical basis for the scientific storage and quality regulation, and technical support for the sales of stocked KJGT. • Kejia green tea stored for 10 years had the best flavor quality. • Storage significantly reduced bitter and astringent substances. • Seven key volatile metabolites regulated the aroma of aged tea. • Storage significantly reduced the high-fire aroma, while enhancing the aroma.