Metabolomics analysis reveals the patterns and mechanisms of volatile metabolite in oolong tea during storage

Oolong tea is famous for its rich floral and fruity aroma which further develops into a distinct aged aroma over time. Storage plays an important role in the quality of the aroma. However, the precise aroma characteristics and profile components of long-term stored oolong tea have not been fully elucidated. In this study, we adopted gas chromatography-mass spectrometry (GC-MS) in combination with multivariate statistical analysis to investigate the dynamic changes in volatile metabolites of oolong tea during different storage periods. Our findings revealed 14 aroma components that served as markers distinguishing aged oolong tea from new tea. With storage years increased, the characteristic woody aroma components of (6,6-dimethyl-2-bicyclo[3.1.1]hept-2-enyl)methanol, 3,5,5-trimethylcyclohex-2-en-1-one gradually increased. Additionally, specific floral and fruity aroma components, such as 2-(4-methylcyclohex-3-en-1-yl)propan-2-yl acetate, 2-[(1S)-4-methylcyclohex-3-en-1-yl]propan-2-ol, ethyl 3-(furan-2-yl)propanoate were also found to be accumulated year by year, contributing to the woody, floral, and fruity character observed in aged tea. 5-Methyl-6,7-dihydro-5H-cyclopentapyrazine decreased regularly during storage. KEGG enrichment analysis demonstrated that the significant enrichment pathways of differential volatile metabolites were primarily related to metabolic pathways and the biosynthesis of secondary metabolites. This study provided a comprehensive understanding of the changes in volatile metabolites and aroma quality of oolong tea during storage, thereby providing guidance for the optimal storage conditions of oolong tea.