Effects of Freezing Methods on Lipid Oxidation and Microstructure of Muscle Fibers in Acipenser sinensis

This study was executed in order to investigate quality deterioration caused by lipid oxidation during the frozen storage of Acipenser sinensis. Fish pieces were stored at -18 ℃ for 24 weeks after being frozen using a freezer (-20 or -50 ℃) or liquid nitrogen (-80 or -110 ℃). The central temperature, fat and free fatty acid (FFA) contents, fatty acid composition, peroxide value (POV), thiobarbituric reactive substance (TBARS) value, and fluorescent compound content were measured and the microstructure of muscle fibers was also observed during the storage period for the purpose of evaluating the influence of freezing methods on lipid oxidation and muscle microstructure in Acipenser sinensis during frozen storage. The results showed that with increasing storage time, the fat and polyunsaturated fatty acid (PUFA) contents of the four fish samples decreased, while POV, TBARS value, and the contents of FFAs, saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) and fluorescent compounds increased. The gap between muscle fibers increased, which was accompanied by breaking of myofibrils. In addition, the contents of fat and PUFAs in liquid nitrogen frozen samples were significantly higher than those in freezer frozen ones (at the end of storage, the freezer frozen sample frozen at -20 ℃ contained 7.89% of fat compared to 9.13% for the liquid nitrogen frozen one at -80 ℃), while POV, TBARS value, and the contents of FFAs, SFAs, MUFAs and fluorescent compounds were significantly lower than those in freezer frozen samples (P < 0.05), and the muscle fiber structure was more complete. The above results indicated that liquid nitrogen frozen alleviated the degree of myofibrillar damage and lipid hydrolysis in Acipenser sinensis during frozen storage, thereby reducing the speed of lipid oxidation.