Changes in the volatile compounds and characteristic aroma during liquid-state fermentation of instant dark tea by Eurotium cristatum

Instant dark tea (IDT) was prepared by liquid-state fermentation inoculating Eurotium cristatum. The changes in the volatile compounds and characteristic aroma of IDT during fermentation were analyzed using gas chromatography-mass spectrometry by collecting fermented samples after 0, 1, 3, 5, 7, and 9 days of fermentation. Components with high odor activity (log2FD ≥ 5) were verified by gas chromatography–olfactometry. A total of 107 compounds showed dynamic changes during fermentation over 9 days, including 17 alcohols, 7 acids, 10 ketones, 11 esters, 8 aldehydes, 37 hydrocarbons, 4 phenols, and 13 other compounds. The variety of flavor compounds increased gradually with time within the early stage and achieved a maximum of 79 compounds on day 7 of fermentation. β-Damascenone showed the highest odor activity (log2FD = 9) in the day 7 sample, followed by linalool and geraniol. These results indicate that fungal fermentation is critical to the formation of these aromas of IDT.