Abstract: The objective of this study was to evaluate the effects of freeze-thaw (F-T) cycles on the lipid changes in dark meat of cooked bonito. The peroxide value (POV), acid value (AV), pH, lipid composition and fatty acid composition were determined after 0, 2, 4, 6 and 8 F-T cycles. The results showed that lipid composition significantly changed, and the contents of triacylglycerol (TAG) and polar lipid (PL) decreased significantly, while the content of free fatty acids (FFA) increased significantly with the number of F-T cycles. In addition, the POV and AV increased significantly, while the pH decreased (P < 0.05). The contents of total saturated fatty acids and total polyunsaturated fatty acids in the total lipids decreased gradually, the contents of fatty acids in TAG and PL and the content of total polyunsaturated fatty acids in PL decreased significantly, whereas the content of total polyunsaturated fatty acids in FFA increased significantly (P < 0.05). Principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) showed that there were differences in lipid profile among fish subjected to different F-T cycles, and the degree of lipid oxidation increased with the number of F-T cycles. Finally, correlation analysis showed that the content of FFA was positively correlated with AV and POV, but negatively correlated with pH and the contents of PL and TAG. These results indicated that F-T cycles could affect the lipid composition of dark meat of cooked bonito and induce lipid oxidation and decomposition, which may provide some theoretical guidance for lipid control of dark meat of cooked bonito during storage and transportation.

Key words: dark meat of cooked bonito; freeze-thaw cycles; lipid composition; lipid oxidation; fatty acids