Influence of frozen storage temperature on the microstructures and physicochemical properties of pre-frozen perch (Micropterus salmoides)

The objective of this work was to investigate the effect of frozen storage temperature on the ice crystal microstructure and physicochemical properties of pre-frozen perch. Perch cube were stored at -18, -40, -80 degrees C and liquid nitrogen (-196 degrees C) respectively for one month after pre-frozen in liquid nitrogen for 1 h. With the increase of storage temperature from -80 to -18 degrees C, temperature-dependent relationship was applicable: cell space, area and amount of ice crystals in frozen samples were gradually increased, Ca2+-ATPase activity and total sulfhydryl content of myofibrillar protein extracted from frozen samples decreased significantly (P < 0.05), shear force and salt-soluble protein content of perch tissues were significantly decreased (P < 0.05), while expressible moisture were increased (P < 0.05). Therefore, -80 degrees C was recommended as the appropriate storage temperature for pre-frozen perch. Liquid nitrogen was not fit for long-term storage due to the destructive effect on fish quality.