New insights into the function of lipid droplet‐related proteins and lipid metabolism of salt‐stimulated porcine biceps femoris: label‐free quantitative phosphoproteomics, morphometry and bioinformatics.

Background: Lipid droplets (LDs) are important multifunctional organelles responsible for lipid metabolism of postmortem muscle. However, the dynamics in their building blocks (cores and layers) and phosphorylation of lipid droplet‐related proteins (LDRPs) regulating meat lipolysis remain unknown at salt‐stimulated conditions. Results: LDRPs extracted from cured porcine biceps femoris (1% and 3% salt) were subjected to label‐free quantitative phosphoproteomic analysis and LDs morphological validation. Results indicated that 3% salt curing significantly decreased triglyceride (TG) content with increase in glycerol and decrease in LDs fluorescence compared to 1% salt curing. Comparative phosphoproteomics showed that there were significant changes in phosphorylation at 386 sites on 174 LDRPs between assayed groups (P < 0.05). These differential proteins were mainly involved in lipid and carbohydrate metabolism. Curing of 3% salt induced more site‐specific phosphorylation of perilipin 1 (PLIN1, at Ser81) and adipose triglyceride lipase (ATGL, at Ser399) than 1%, whereas the phosphorylation (at Ser600) of hormone‐sensitive lipase (HSL) was up‐regulated. Ultrastructure imaging showed that LDs were mostly associated with mitochondria, and the average diameter of LDs decreased from 2.34 μm (1% salt) to 1.73 μm (3% salt). Conclusion: Phosphoproteomics unraveled salt‐stimulated LDRPs phosphorylation of cured porcine meat provoked intensified lipolysis. Curing of 3% salt allowed an enhanced lipolysis than 1% by up‐regulating the phosphorylation sites of LDRPs and recruited lipases. The visible splitting of LDs, together with sarcoplasmic disorganization, supported the lipolysis robustness following 3% salt curing. The finding provides optimization ideas for high‐quality production of cured meat products. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]