Non-targeted metabolomics and electronic tongue analysis reveal the effect of rolling time on the sensory quality and nonvolatile metabolites of congou black tea

Rolling is a crucial step in congou black tea manufacturing. Herein, the influence of rolling time (50, 75, 100, 125 min) on the sensory quality and chemical composition of black tea was investigated by human sensory evaluation, electronic tongue, colorimetric analysis, tea pigments quantification and liquid chromatography-mass spectrometry (LC-MS) based non-targeted metabolomics. With increasing rolling time, tea liquor color attributes a*, b*, C* and pigments theaflavins (TFs), thearubigins (TRs), and theabrownins (TBs) were significantly increased. Fifty-two key differential metabolites were identified among four treatments. Catechins, dimeric/trimeric catechins, amino acids were significantly declined. The changes of flavonol/flavone glycosides depended on the linkage pattern. Flavonol O -glycosides such as myricetin 3- O -glucoside were decreased, whereas flavone C -glycosides such as vitexin were increased. These results suggested that different rolling times influenced the catechins oxidative polymerization, flavonol O -glycosides hydrolysis and amino acids oxidation. Black tea by 100-min rolling rendered optimal sensory quality, with highest umami and low bitter intensities in electronic tongue, and higher quality index (10 TFs + TRs)/TBs. Similar result was obtained in a validation batch in a different year. This study provides novel insights into the effect of rolling on black tea quality, which may serve as guidance for the manufacturing of high-quality congou black tea.