Comprehensive comparison on the chemical metabolites and taste evaluation of tea after roasting using untargeted and pseudotargeted metabolomics

Roasting is a common manufacture technology for processing various teas. It is not only used in decreasing the water content of finished tea, but also improving the flavor of teas. In the present study, the roasted and non-roasted teas were compared by liquid-chromatography mass spectrometry and sensory evaluation. The roasted tea tasted less bitter and astringent. The content of main galloylated and simple catechins, caffeine and theobromine in roasted were significantly lower than non-roasted teas. Targeted taste-compounds metabolomics revealed that (–)-epigallocatechin gallate, kaempferol-glucose-rhamnose-glucose and (–)-epicatechin gallate were main contributors tightly correlated to astringent intensity. Flavonol glycosides including kaempferol-glucose, quercetin-glucose, kaempferol-glucose-rhamnose-glucose, and quercetin-glucose-rhamnose-glucose in roasted teas were also significantly less than non-roasted teas. To study the chemical changes during roasting, tea with a strong astringency was roasted under 80, 100, 120, 140, and 160 °C. With the increase of roasting temperature, the bitter and astringent intensity of tea was gradually decreased, but the main astringent compounds including (–)-epigallocatechin, (–)-epigallocatechin gallate and kaempferol/quercetin glycosides were irregularly varied with temperature. The Pearson correlation coefficient analysis suggested procyanidin B2, coumaroylquinic acids and gallotannins were tightly correlated to the astringent and bitter perceptions, while N-ethyl-2-pyrrolidone-substituted flavan-3-ols were negatively correlated.