Exploring the lipid changes and oxidative degradation mechanisms during walnut kernel storage based on lipidomics

The oxidative stability of walnut kernels during storage has a significant impact on their industrial development. However, the effect of storage conditions on the oxidation of walnut kernel lipids and its mechanism have not been systematically elucidated. Therefore, in this study, the lipid oxidation process in walnut kernels under different storage conditions (room temperature-air, room temperature-vacuum, low temperature-air, and low temperature-vacuum) was systematically studied from the perspective of phenomena, substances, and mechanisms using HPLC–MS and GC–MS methods. Experimental results found the walnut kernels stored at room temperature in air showed the highest PV (7.78 mmol/kg), conjugated diene (1.29), and hexanal (848.65 ng/g) after a 9-month storage. A total of 597 lipid substances were detected in walnut kernels under the four storage conditions, including 5 classes and 26 subclasses, of which 115 were significantly different. Differential lipid metabolite analyses indicated that storage conditions mainly affected the glycerophospholipid and glycerolipid metabolic pathways of walnut kernels, followed by linoleic acid metabolism. It revealed that temperature, rather than air conditions, played a dominant role in the lipid oxidation of walnut kernels during storage. This experiment could provide a comprehensive understanding of the lipid oxidation of stored walnut kernels and technical support for quality control.

Graphical abstract