Changes in Non-Volatile Components in Liupao Tea during Aging

Sensory evaluation, quantitative chemical analysis, and untargeted metabolomics based on ultra-high performance liquid chromatography-quadrupole exactive orbitrap-mass spectrometry (UPLC-Q-Exactive-MS) were applied to investigate the pattern of changes in the major non-volatile components of Liupao tea during the aging process. Tea samples were collected before aging and after 1 to 6 months of aging. The results showed that as aging progressed, the tea infusion gradually turned a deeper and brighter red; the aroma evolved toward a sweeter and more aged profile, and the taste became progressively mellower, with a significant improvement in overall sensory quality. Quantitative chemical analysis revealed that the levels of tea polyphenols, free amino acids, caffeine, and flavonoids decreased with aging time, while that of theabrownins significantly increased (P < 0.001). Metabolomic profiling identified a total of 164 non-volatile compounds, among which 48 were classified as key differential metabolites based on variable importance in projection (VIP) values and statistical significance (P < 0.05). Among these, 9 metabolites such as xanthine were significantly up-regulated after 6 months of aging, while 39 metabolites such as 5-methyluridine were significantly down-regulated. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that metabolic pathways related to caffeine, purines, and pyrimidines played crucial roles in regulating the relative abundance of these key differential metabolites, thereby contributing to the development of the flavor quality of Liupao tea.