Characteristic volatiles of Fu brick tea formed primarily by extracellular enzymes during Aspergillus cristatus fermentation.

Schematic diagram for the sources of typical volatiles of Fu brick tea. RDT: volatiles from raw dark tea; ECE: volatiles formed from the extracellular enzymes pathways of Aspergillus cristatus ; typicalFBT: typical volatiles of Fu brick tea; non-Contributor: volatiles with a ROAV below 1 were considered to be unable to contribute to the aroma; FBTaroma: volatiles with ROAV over 1 were considered as aroma contributors to Fu brick tea. [Display omitted] • Volatile profiles of Aspergillus cristatus were rich in 1-octen-3-ol and 3-octanone. • 44 volatiles varied notably in all 3 groups of Fu brick tea after fermentation. • 1-Octen-3-ol increased dramatically after Fu brick tea fermentation. • Volatile profiles of Fu brick tea and parallel fungal cultures varied considerably. • Formation of key aroma compounds was mainly via microbial extracellular enzymes. Fu brick tea (FBT) has unique "fungal flower" aroma traits, but its source of crucial aroma compounds is still controversial. Aspergillus cristatus is the dominant fungus that participated in the fermentation of FBT. In this study, volatiles of Aspergillus cristatus and corresponding fermented FBT were examined using GC × GC-Q-TOFMS. A total of 59 volatiles were shared by three strains of Aspergillus cristatus isolated from representative FBT. Among them, 1-octen-3-ol and 3-octanone were the most abundant. A total of 133 volatiles were screened as typical FBT volatiles from three FBTs fermented by the corresponding fungi. Aspergillus cristatus and FBT had only 29 coexisting volatiles, indicating that the volatiles of Aspergillus cristatus could not directly contribute to the aroma of FBT. The results of no significant correlation between volatile content in FBT and volatile content in Aspergillus cristatus suggested that intracellular metabolism of Aspergillus cristatus was not a direct driver of FBT aroma formation. Metabolic pathway analysis and proteomic analysis showed that the aroma in FBT was mainly formed by the enzymatic reaction of extracellular enzymes from Aspergillus cristatus. This study enriched our understanding of Aspergillus cristatus in the aroma formation process of FBT. [ABSTRACT FROM AUTHOR]