Determination of the variations in the metabolic profile and sensory quality of Liupao tea during fermentation through UHPLC–HR–MS metabolomics

Liupao tea is a dark tea with unique quality. Semi-finished Liupao tea with two different fermentation processes (traditional/tank) was analyzed to explain the chemical characteristics and taste quality. The content change rate of polyphenols, flavonoids, and theabrownin in traditional fermentation was approximately twice that in tank fermentation. Electronic tongue revealed that bitterness and astringency increased, whereas aftertaste-astringency decreased after fermentation. 36 compounds were identified as the biomarkers responsible for the metabolic changes caused by fermentation with significant decrements in catechins, catechin gallate, and α, α-trehalose, and significant increments in gallic acid content (VIP > 3; P < 0.05). In addition, 26 metabolites were identified to distinguish between tank and traditional fermentation, with correlation analysis indicating that catechin gallate, epicatechin and gallic acid accounting for the differences in taste between the two processes. This study provides a comprehensive insight into the chemical composition and sensory quality of different Liupao tea fermentations.