Multi-omics and quantitative technique reveal the effects of post-fermentation on the metabolites and flavor quality of sea buckthorn leaves tea

• Multi-omics revealed metabolic reconfiguration during post-fermentation. • 3316 non-volatile and 1593 volatile metabolites were identified. • Fermentation promoted alkaloid and flavonoid accumulation. • Cucumber-like, green, and roasted nutty notes were associated with volatile shifts. Fermentation is a critical determinant in shaping the flavor and functional attributes of food. However, the metabolic alterations and flavor formation mechanisms in post-fermented sea buckthorn ( Hippophae rhamnoides L.) leaves tea remain unclear. In this study, the chemical profile and flavor formation mechanisms were investigated using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS), and quantitative analysis. A total of 3316 non-volatile and 1593 volatile metabolites were identified. Fermentation markedly enhanced alkaloids such as neohesperidin A and 8-methyltheophylline, as well as flavonoids including vitexin 4′'- O -rhamnoside, kaempferol derivatives, and isovitexin. Aroma-active volatiles such as ( E,Z )-2,6-nonadienal, 2-methoxy-3- (1-methylethyl)-pyrazine, and dimethyl trisulfide were associated with cucumber-like, green, and roasted-nutty sensory notes. Meanwhile, sugar and amino acid degradation, catechin hydrolysis, and theabrownin-like polymer formation contributed to a deeper liquor color and enhanced flavor complexity. These findings provide mechanistic insights into how fermentation reshapes the metabolome of sea buckthorn leaves tea, providing a scientific basis for the value-added utilization of sea buckthorn leaves.