Metabolites and microbial characteristics of Fu brick tea after natural fermentation

Abstract

Fu brick tea is made from pre-fermented tea through fermentation and other complicated processes. After fermentation, the microbes and metabolites are changed. Liquid chromatography-mass spectrometry, untargeted metabolomics, and 16 S rDNA and internal transcribed spacer sequencing were used to study metabolites and microorganisms in pre-fermented tea and Fu brick tea fermented for 6 months. Among the seven flavor-related metabolites detected by liquid chromatography–mass spectrometry, only epigallocatechin significantly increased, which can be used as a marker metabolite of Fu brick tea. In total, 292 differentially accumulated metabolites were obtained using untargeted metabolomics, and they were mainly enriched in gingerol biosynthesis and other health-related metabolic pathways. Eurotium cristatum, which accounted for more than 99% of all fungi, and gamma-Proteobacteria may be used as the signature microorganisms of Fu brick tea. Correlation analysis showed that 2-formylglutarate was the metabolite with the strongest correlation with Aspergillaceae and was of great significance for fermentation. In the phenylpropanoid biosynthetic pathway, microorganisms and metabolites were significantly enriched. The changes in metabolites and microbes in pre-fermented tea and Fu brick tea provide important information for analyzing the interactions between microbes and metabolites and improving the characteristics of Fu brick tea.