Lipid oxidation driven olefinic aldehyde biosynthesis shapes aged aroma in Qingzhuan tea

This study systematically investigates lipid dynamics and their role in aroma formation during Qingzhuan tea (QZT) processing. Using UHPLC-MRM-MS/MS and GC-MS, we analyzed fatty acids (FAs) and oxidized fatty acids (OFAs) across seven processing stages, identifying 31 FAs and 55 OFAs. Polyunsaturated fatty acids (PUFAs), particularly α-linolenic acid (C18:3) and linoleic acid (C18:2), dominated the lipid profiles (43.7 %-60.1 %), exhibiting biphasic dynamics: a 5.3-fold increase during pile fermentation and natural aging (RT → A12) followed by oxidative degradation (30.0 % reduction in QZT). Multivariate analysis revealed 76 differential lipids correlating with 22 key volatiles, including (E,E)-2,4-heptadienal and (E)-2-octenal. Metabolic pathway analysis mapped lipoxygenase/cyclooxygenase (LOX/COX)-mediated oxidation of C18:3/C18:2 to hydroperoxides, which were then cleaved by lyases into aldehydes. Isotope labeling confirmed cross-pathway interactions between linoleic and arachidonic acid metabolism, while modeling experiments validated enzymatic generation of C6-C9 aldehydes from lipid precursors. This work elucidates the biochemical basis of QZT's aged aroma, providing actionable insights for flavor modulation in fermented teas.