Effects of rolling temperature on green tea flavor from integrated metabolomics and flavor quantification

Rolling is a crucial process in determining tea quality. However, the impact of the rolling temperature on the transformation mechanisms of non-volatile and volatile metabolites is unclear. In this study, we aimed to explore the impact of rolling temperature (15 °C, 25 °C, and 35 °C) on green tea quality by detecting the quality components of non-volatile and volatile metabolites, combined with an objective evaluation. Seventeen objective indicators were obtained, and 55 non-volatile metabolites (NVMs) and 60 volatile metabolites (VMs) were identified. Rolling at 15 °C increased the tea liquor greenness, color saturation, and umami taste by 42.68%, 40.44%, and 3.42%, respectively. Through multivariate statistical analysis, dose-over-threshold and odor activity values, six key NVMs, and six key VMs were identified. Green tea rolled at 15 °C exhibited higher theanine (2.29%) and epigallocatechin (3.53%) contents, along with lower quercetin 3-O-glucoside (0.65%) content, which enhanced the sweetness and umami of the tea liquor. Rolling at 15 °C promotes glycoside hydrolysis while suppressing isoleucine degradation and fatty acid oxidation. This favors the accumulation of the floral aroma compound geraniol and reduces the levels of grassy odorants (2-methylbutyraldehyde and 1-octen-3-ol), improving the aroma quality of green tea. The findings provide theoretical guidance for precise green tea processing.