Dynamics changes in volatile profile, non-volatile metabolites and antioxidant activities of dark tea infusion during submerged fermentation with Eurotium cristatum

Eurotium cristatum is a dominant fungus in the post-fermentation of Fu brick tea, however, its potential role in affecting the volatile profile and non-volatiles metabolites during the liquid-state fermentation of dark tea is not clear. In this study, dark tea was prepared by liquid-state fermentation with E. cristatum. A total of 51 volatile compounds were identified by HS-SPME-GC-MS, which mainly consisted of ketones, aldehydes, esters, and alcohols. There were 12 volatiles (ROAV >1) contributed to the overall aroma, including linalool, citral, methyl salicylate, etc. The overall flavor of tea infusion had been greatly improved after fermentation. The content of ester-type catechins, total phenols, total flavonoids, theaflavins, thearubigins, soluble sugars, and free amino acids decreased, while the content of theabrownins and soluble proteins increased. Meanwhile, the content of nonester type catechins and gallic acid increased and then decreased. The contents of various volatiles and metabolites change under the action of E. cristatum, coordinating to form a fermented dark tea infusion with mint, flower and fruit aroma and mellow and slightly astringent quality. The antioxidant activities showed a positive correlation with substances such as gallic acid and polyphenols. The results showed that the liquid-state fermentation with E. cristatum can effectively influence the flavor characteristics and antioxidant capacity of dark tea infusion.