Impact of Aspergillus cristatus dominated fermentation on fungal communities and metabolite profiling in large-leaf Tea: Insights into quality formation via post-fermentation “flowering” process

Abstract

Large-leaf tea is an important raw material for tea processing. The post-fermentation process of Fu brick tea with Aspergillus cristatus as the dominant microorganism is described as "flowering", which can strongly alter the metabolites in tea. However, the changes in fungal community abundance and metabolites of large-leaf tea after flowering are not clear at present. In this work, fungal communities, nonvolatile metabolites and volatile metabolites were detected in large-leaf tea before and after flowering using full-length nuclear ribosomal internal transcribed spacer region sequencing and untargeted metabolomic techniques. The full-length sequencing revealed that the percentage of unclassified_f_Aspergillaceae in large-leaf tea after flowering reached 92.31 %, and the dominant fungus among them was confirmed to be Aspergillus cristatus based on the multilocus sequences. The content of epigallocatechin, catechin gallate, and catechin decreased by 24.88 %, 22.42 %, and 45.11 % (w/w), respectively, while the content of gallic acid increased by 98.75 % after flowering. A total of 30 key differential volatile metabolites were identified. Among them, α-ionone, linalool, linalool oxide II, methyl salicylate and geranyl acetone increased by 172.4 %, 110.6 %, 200.0 %, 349.8 %, and 176.9 % (w/w) after flowering. These increased volatiles were mainly described as flowery odors. Correlation analyses of metabolites and microorganisms showed an extremely strong correlation between changes in fungal abundance and metabolite content. Our findings provided experimental evidence for the alteration of metabolite profiles in large-leaf tea by flowering and a new strategy for the post-fermentation process of large-leaf tea.