Influence mechanism of fixation on the development of green tea flavor and related non-volatile and volatile metabolites by objective quantification, widely targeted metabolomics, and aroma metabolomics

Fixation is key for green tea flavor formation; however, the impact of fixation methods on non-volatile metabolites (NVMs) and volatile metabolites (VMs) regulation remains unclear. We applied objective quantification techniques, widely targeted metabolomics, and aroma-omics to analyze the influence of fixation methods on green tea quality. Roller-hot air coupling fixation (RHF) produced an umami taste with a chestnut aroma, whereas roller-steam coupling fixation (RSF) produced a tender aroma with bitterness. We detected 498 NVMs and 63 VMs, and 14 key quality-differential NVMs and 7 key VMs were identified. KEGG revealed flavonoid, amino acid, glycoside, and carotenoid metabolism were the key pathways caused by fixation methods resulting in green tea flavor difference. RHF accelerated flavonoid transformation and amino acid formation metabolism, resulting in higher L-glutamic acid and catechin contents, lower rutin and l -lysine contents. These results provide a theoretical and technical support for precise targeted processing of high-quality green tea.