This study investigated the dynamic changes of volatile compounds, bioactive components and microbial communities during the solid-state fermentation of Fu brick tea (FBT). Gas chromatography-ion mobility spectrometry (GC-IMS) and previously reported methods were used to analyze volatile substances and bioactive constituents. Microbial community succession was characterized by 16S rDNA and internal transcribed spacer (ITS) sequencing, and the correlations between the dominant taxa and the bioactive components and volatile compounds were examined. GC-IMS analysis identified 109 compounds, the main ones being alcohols, aldehydes, ketones, and esters. Among them, the contents of 4,5-dimethylthiazole, S-propyl thioacetate, and isopropyl isothiocyanate decreased, while those of butyl propionate, 3-methyl-2-cyclopentenone, and 5-methylfuranal increased. Microbial community analysis showed that the fungal community was predominantly composed of Ascomycetes, with Aspergillus being the dominant genus; the bacterial community was mainly composed of Proteobacteria. The fungal genera Eurotium, Candida, and Fusarium, and the bacterial genera Glutamicibacter, Corynebacterium, and Lactiplantibacillus were significantly correlated with the bioactive components of FBT. Shifts in the microbial community led to changes in the composition of volatile substances. In particular, in the late stage of fermentation, Pseudomonas and Aspergillus contributed to the formation and stabilization of the unique aroma characteristics of FBT, such as floral, fruity, and pine-like. To sum up, microbial community dynamics significantly affected the formation of volatile substances, functional ingredients and quality of FBT. This study provides a theoretical basis and new ideas for the development and quality control of new FBT products and the utilization of FBT resources.

In order to investigate the changes of metabolite profile during the fermentation of ‘Golden Flower’ Eucommia ulmoides leaf tea, quantitative, qualitative and differential analyses of small molecule metabolites in tea samples at different fermentation times (0, 2, 4, 6, 8 and 10 days) were carried out using ultra-high performance liquid chromatography-quadrupole time of flight mass spectrometry (UPLC-Q-TOF-MS). The results showed that 172 significantly differential metabolites, belonging to 13 chemical classes, were identified during the entire fermentation process, including 46 flavonoids, 44 fatty acids, 16 amino acids and 11 organic acids. Furthermore, by selecting significantly differential metabolites at different fermentation times, it was found that the bioactive substances whose contents significantly increased after fermentation included flavonoids, fatty acids and organic acids. These metabolites played an important role in enhancing the taste and aroma of the tea. After fermentation, the contents of the differential metabolites L-glutamine, 20-hydroxyeicosatetraenoic acid, glucuronic acid, trans-ferulic acid, norvaline and auriculoside increased. The fermented tea had health functions such as antioxidant, hypotensive, detoxicating, anti-inflammatory and immunoenhancing effects compared with the unfermented tea. Therefore, fermentation can significantly alter the metabolite profile of E. ulmoides leaf tea, which plays an important role in the formation of the taste and aroma quality and antioxidants of fermented E. ulmoides leaf tea.