The Regulatory Mechanism of Salt-Induced Lipid Metabolism in Porcine biceps femoris Through Proteomic Analysis of Lipid Droplets

Lipid metabolism during curing of meat products is an essential biological process that affects their eating quality. Lipid droplets (LDs) are the main sites for storing neutral lipids and participating in lipid metabolism, and their surface lipid droplet-related proteins (LDRPs) directly regulate lipid degradation. In this study, we analyzed the expression changes of LDRPs in porcine biceps femoris muscle under curing conditions (1% and 3% salt concentration) by proteomics and discussed the role played by LDs in the regulation of lipid metabolism. A total of 1127 quantitative proteins were identified by mass spectrometry. Among them, the differential proteins between the control and cured groups were mainly involved in biological processes such as lipid metabolism and carbohydrate metabolism. Protein quantification results showed that RAB18 expression was downregulated after curing, suggesting that curing caused LDs to become small and dispersed. Besides, the expression trends of proteins responsible for macroautophagy (RAB7 and RAB10) and those responsible for CMA (HSPA8 and PLIN2) in LDs were opposite. The upregulation of CPT2, ACADL, FABP4, and FABP5, which were related to fatty acid transport and β-oxidation, intensified the degradation of fatty acid in cured samples. Consequently, we concluded that curing promoted LD degradation. Macroautophagy, CMA, and lipolysis were likely to occur alternately and synergistically during the degradation process. The results have significant implications for our understanding of the metabolic processes involved in lipid molecules during meat processing.