Dynamic changes in the metabolite profile and taste characteristics of loose-leaf dark tea during solid-state fermentation by Eurotium cristatum

Loose-leaf dark tea fermented by Eurotium cristatum has increasingly gained favor in the market due to its unique fungal aroma and soft mouthfeel. In this study, the dynamic changes in the metabolite profile and taste characteristics of loose-leaf dark tea were investigated. Ninety-two critical metabolites were identified during fermentation by ultraperformance liquid chromatography coupled with Q-Exactive Orbitrap tandem mass spectrometry (UPLC-Q-Exactive Orbitrap/MS). Among these metabolites, catechin derivatives were converted to numerous other metabolites, such as fuzhuanin A and teadenol A, by the metabolic activity of E. cristatum, which were significantly increased in the later stages of fermentation. Taste evaluation and targeted metabolomics demonstrated that the intensities of astringency, bitterness, umami and sourness of the tea infusions gradually weakened with declines in the contents of ester-catechins and amino acids, while the intensities of color, sweetness and stale taste gradually developed during fermentation with increases in the contents of theabrownins and tea polysaccharides. These results revealed the important contribution of E. cristatum to the formation of the compounds that impart the unique taste of loose-leaf dark tea and provide a chemical basis for quality control during dark tea processing.