Ultrasound-assisted immersion freezing accelerates the freezing process and improves the quality of common carp (Cyprinus carpio) at different power levels

This study evaluated the effect of ultrasound-assisted immersion freezing (UIF) on the freezing speed and quality of common carp (Cyprinus carpio) at different ultrasonic power levels. The results revealed that UIF increased the speed of freezing, with UIF at 175 W (UIF-175) being optimal. Compared to refrigerator freezing and immersion freezing, UIF samples had less thawing and cooking loss. Microstructural observation showed that UIF-175 reduced pore diameter and ice crystal size. As ultrasonic power increased, the L*-value first decreased and then increased (P < 0.05), and there were no significant differences in a*- or b*-values (P > 0.05). UIF-175 samples exhibited the shortest T-21 and T-22 relaxation time, which indicated that this appropriate ultrasonic power level reduced the mobility of free and immobilized water. Therefore, UIF at appropriate ultrasonic power significantly decreased the freezing time of fish samples and improved the fish meat quality.