Abstract: In order to investigate the formation mechanism of the quality of baked green tea, we used metabolomics based on ultra-high performance liquid chromatography-quadrupole-Exactive mass spectrometry (UPLC-Q-Exactive/MS) to analyze the differences in the chemical compositions of green tea samples at different stages of thermal processing such as fixation, drying and roasting. A total of 125 compounds were identified, including 10 flavanols, 14 dimeric catechins, 19 flavanol-O-glycosides, 5 flavone-C-glycosides, 8 N-ethyl-2-pyrrolidinone-substituted flavan-3-ols (EPSF), 16 amino acids, 13 phenolic acids, 4 organic acids, 11 alkaloids, 13 lipids, 4 aroma glycosides and 8 other compounds. The results of partial least squares-discriminant analysis (PLS-DA) and heat map analysis showed that the chemical components obviously changed during the thermal processing of green tea, and 114 significantly differential compounds were selected (P < 0.05). In the three stages of thermal processing, the contents of most catechins and dimeric catechins decreased, and the contents of EPSFs, flavone- C-glycosides, and lipid compounds significantly increased. The contents of aroma glycosides (phenylethyl primeveroside, linalool primeveroside, and linalool oxide primeveroside) increased by 439% to 2 497% during the fixation process. The content of N-(1-deoxy-D-fructosyl)theanine increased by 820% to 1 290% during the drying process. The contents of flavanol-O-glycosides (myricetin 3-galactoside, kaempferol-3-galactoside, kaempferol 3-arabinoside, myricetin 3-glucoside and kaempferol-3-glucoside) decreased significantly during roasting. This study can provide a theoretical reference for future improvement of green tea quality.

Key words: green tea; thermal processing; metabolomics; liquid chromatography-mass spectrometry; chemical components