Exploring the oxidative rancidity mechanism of walnut oil during storage based on lipidomics

Walnut oil (WO) is rich in nutrients; however, it is susceptible to oxidative rancidity caused by external factors during storage. This susceptibility is also related to its own lipid composition, metabolism, and other factors. At present, no comprehensive study has investigated lipid group changes during the oxidation process of WO. Lipid changes in WO over 24 d of accelerated oxidation were dynamically monitored via high-performance liquid chromatography-triple quadrupole tandem mass spectrometry, revealing 354 lipids across 15 subclasses. Among these lipids, ceramide, phosphatidylcholine, triglyceride, diglycerides, and total ester exhibited significantly decreased levels (P < 0.05), while phosphatidylinositol and phytoceramide yielded significantly increased contents (P < 0.05). Using multivariate statistical analysis, 22 differential lipids (variable importance in projection >1, P < 0.05) were screened as markers to identify the degree of WO oxidation. Through Kyoto Encyclopedia of Genes and Genomes pathway analysis, seven major metabolic pathways were elucidated to investigate the underlying oxidative mechanisms. This study offers novel insights into and lays a theoretical foundation for exploring the storage stability of WO and the mechanisms underlying lipid oxidation.