Oxygen-driven evolution of volatile and nonvolatile metabolites in Hainan Dayezhong black tea: a comparative study of aerobic ventilation versus airtight fermentation

Hainan Dayezhong is a distinctive tea plant resource in Hainan, possessing abundant flavor compounds and bioactive components; however, the impact of the fermentation oxygen environment on metabolites during black tea processing remains unclear. This study systematically investigates the impact of aerobic fermentation on the dynamic changes of volatile metabolites (VMs) and non-volatile metabolites (NVMs) during the processing of Hainan Dayezhong black tea. Integrating E -nose, E-tongue, HS-GC-IMS, HS-SPME-GC–MS, and UPLC-MS/MS techniques with multivariate statistical methods, we identified 1436 (GC–MS) and 45 (GC-IMS) distinct VMs and 3380 NVMs. The results indicate that aerobic fermentation can activate the synergistic metabolism of endogenous enzymes and microorganisms in tea, promoting the generation and accumulation of aromatic compounds such as esters, terpenes, and heterocyclic substances. The major volatiles, such as linalool, methyl benzoate, 1-hexanol, and (±)-myrtenol, collectively contribute to the floral, fruity, and sweet aromas of tea. Meanwhile, oxygen can regulate the transformation of non-volatile compounds such as polyphenols, flavonoids, amino acids, and lipids, reducing the proportion of bitter and astringent substances and enhancing the fresh and sweet taste of tea infusion. Compared to airtight fermentation, aerobic fermentation improves aroma and taste quality through pathways such as lipid metabolism, phenylpropanoid metabolism, and carbohydrate metabolism. This study demonstrates that aerobic fermentation can promote the formation of flavor-related metabolites, providing a theoretical basis for optimizing black tea processing.