Mechanism of the effect of fixation degrees on the volatile and non-volatile metabolites in green tea using targeted and non-targeted metabolomics analyses and the flavor objective quantification technique.

Fixation plays a crucial role in green tea processing; however, the impact of different fixation degrees on the conversion of non-volatile and volatile metabolites remains unclear. This study explored the effects of mild, moderate, and severe fixation on green tea quality and identified 53 non-volatile metabolites, 60 volatile metabolites, and 17 objective flavor indicators. Moderate fixation (55 % leaf moisture) enhanced the umami and greenness of liquor by 38.91 % and 5.52 %, respectively. Using multivariate analyses, dose-over-threshold, and odor activity values, eight key non-volatile metabolites and three volatile metabolites were identified. Notably, moderate fixation reduced catechin and fatty acid oxidation, glutamic acid decarboxylation, and promoted flavonol glycoside degradation and glycoside hydrolysis. Moreover, it facilitated epigallocatechin gallate (9.49 %), theanine (3.05 %), and linalool formation and accumulation, thereby enhancing the taste and aroma of green tea. This study offers a foundation for optimizing green tea processing to improve tea quality.