Lipidomics Analysis of Lipid Changes in Grass Fish during Cold Storage

In order to identify biomarkers of lipid deterioration in grass carp (Ctenopharyngodon idella) muscle during cold storage, the lipid profile change of the grass carp muscle stored at 4 ℃ for different periods (3, 6, and 9 d) was investigated by UPLC-Q Exactive HF-X. Multivariate statistical analysis and one-way ANOVA were used to screen the differential lipids during the cold storage, and then to enrich the metabolic pathways involved in the differential lipids through the KEGG database. The results showed that the pH in grass carp muscle decreased gradually, while the thiobarbituric acid reactive substance, total free fatty acid content, and volatile base total nitrogen increased gradually, reaching 0.82 µg/kg, 168.22 µg/10 g and 23.63 mg/100 g, respectively, on the 9 d of cold storage. A total of 1265 lipid molecules belonging to 5 categories and 35 subclasses were identified in the chilled grass carp muscle. Glycerol phospholipids (GP) and glycerol esters (GL) were the main components of lipids in grass carp muscle. There was no significant difference in lipid profile between grass carp muscle refrigerated for 3~6 days (P>0.05), but there were significant changes in lipid composition when refrigerated for 9 days. Fatty acyl (FA) and sphingolipids (SP) were the major different lipids in the early stage of refrigeration (3~6 days), and GP was the main lipids with significant changes in the late stage of refrigeration (6~9 days). A total of 20 different lipid molecules were screened from multivariate statistical difference analysis, and they were mainly glycerol ester and glycerol phospholipid, among which PE (16:1e/22:6) showed significant differences (P<0.01). TG (4:0/18:0/22:5), PC (18:1/20:3), and TG (18:0/16:0/20:4) showed significant differences (P<0.05), which could be used as a marker of lipid deterioration in grass carp muscle during the cold storage. Enrichment analysis of the KEGG pathway showed that sphingolipid metabolism and glycerophospholipid metabolism were involved in lipid metabolisms during the cold storage (9 d), which were essential metabolic pathways affecting the deteriorated lipid profile of chilled grass carp. In this study, the differences in lipid profiles, molecular markers of lipid degradation, and their metabolic pathways involved in lipid deterioration of grass carp muscle during cold storage were described. It would provide theoretical guidance for exploring the mechanism of lipid change and related anti-lipid degradation research.