Differential lipid oxidation in various parts of frozen mackerel

Summary Kinetic variations in lipid oxidation in various parts of mackerel stored at −15, −30 and −40°C were studied by measuring the changes of POV and of TBA molar values as a function of time. Oxidation developed in the skin sample (subcutaneous fat) was found to be eight times faster in TBA change than in the white and dark muscles from mackerel held at −15°C for two months. This rapid development of rancidity in the skin was effectively inhibited by lowering the frozen storage temperature to −40°C, where relatively the degree of lipid oxidation in the dark muscle was found to be of the same order of magnitude. the in vitro rate of autoxidation at 60° C for the lipids extracted from skin and the fillet muscle also showed an unusual difference which indicated that unknown pro−oxidative substances in mackerel skin were fat solvent extractable. the activity of the unknown compounds in the skin was also temperature dependent even in the frozen state, but could be effectively mitigated by lowering temperature to −40°C. Lipid hydrolysis in mackerel was also retarded completely when the fish were stored at −40° C. the comparative compositions of fatty acids and volatile carbonyls were determined in head, skin, white and dark muscle, and suggested an active non‐specific oxidation system in the skin fat.