From feed to fillet: Dietary lipid affects sensory quality and fillet lipid profile by modulating lipid metabolism in triploid rainbow trout (Oncorhynchus mykiss)

To investigate the fillet quality traits (texture, flavor, nutritional value) formation and the mechanism of muscular lipid deposition in triploid rainbow trout, low (20%) and high (30%) lipid diets were manufactured and fed market-size triploid rainbow trout (∼3.2 kg) for 77 days. Results showed that the width of the myosepta (MS) was significantly increased, and nonanal, (E, Z)-2,6-nonadienal, octanal, 1-octen-3-ol, and hexanal emerged as the top five contributors to the overall odor profile of the fish fillets, following exposure to the high-lipid (HL) diet. Lipidomic profiling demonstrated that triglycerides (TG) were the predominated lipid class in both muscle fibers (MF) and MS fractions. The HL diet differentially modulated lipid composition: it upregulated TG content in MF, while reducing TG content and promoting the accumulation of phosphatidylcholine (PC) in MS. Gene expression analysis showed tissue-specific regulation of lipid metabolism. In MF, the upregulation of fatty acid binding protein 1 ( fabp1 ) and perilipin-3 ( plin3 ), and the downregulation of fabp2 , peroxisome proliferator activated receptor α ( pparα ), pparβ , acyl-CoA oxidase ( acox ), and carnitine palmitoyltransferase 1 ( cpt1 ), were induced by the HL diet, which collectively promoted TG synthesis and storage, which may be one of the underlying mechanisms contributing to the formation of a more intense odor profile in MF. In MS, HL diet exposure induced the upregulation of fabp2 , pparα , pparβ , acox , and cpt1 , and the downregulation of fabp1 and plin3 , thereby promoting TG mobilization and catabolism, and stimulating PC accumulation, and represent a potential mechanism contributing to the increased width of MS. The findings of this study will lay a theoretical foundation for elucidating the quality formation and the heterogeneity of muscular lipid deposition in rainbow trout. • High-lipid diet (30%) widened myosepta by ~20% and increased key odor-active volatiles, enhancing marbling and flavor intensity of triploid rainbow trout fillets. • Lipidomics identified 2779 lipids, with diet-specific remodeling: triglycerides (76%) accumulating in muscle fibers, while phosphatidylcholine enrichment occurred in myosepta. • Gene expression showed opposite regulation of lipid metabolism between muscle fibers and myosepta, explaining heterogeneous lipid deposition and nutritional fatty acid distribution.