In this study, the effects of ultrasonic-assisted immersion freezing (UIF) with different ultrasonic powers on beef quality were measured. The changes in freezing rate, cooking loss, thawing loss, tenderness, color difference, moisture distribution and microstructure of beef were analyzed after traditional air cooling or ultrasonic-assisted freezing at different ultrasonic powers (0, 200, 400 and 600 W). Fresh beef was used as control. The results showed that UIF could significantly increase the freezing rate of beef, affect the color and water state, and reduce the structural destruction of muscle tissue and quality deterioration during the freezing process. At an ultrasonic power of 400 W, the fastest freezing rate was obtained, as well as the lowest cooking loss and thawing loss of 32.44% and 1.66%, respectively, and shear force closest to that of the fresh meat. In addition, the minimum freezable water of 51.11% was observed. Low-field nuclear magnetic resonance (NMR) analysis showed that the amplitude of T₂₁ was the highest, and the amplitude of T₂₂ was relatively small, indicating a more uniform water distribution. Microscopic observation showed that an appropriate ultrasonic power reduced the structural damage caused by freezing to muscle fibers, thereby improving the quality of frozen meat.

To investigate the effect of different freezing methods on the cooking quality of pork, porcine Longissimus dorsi muscle frozen by three different methods: air freezing (AF), immersion freezing (IF) and ultrasonic-assisted immersion freezing (UIF) were stewed after being thawed at 4 ℃ , and their moisture content, cooking loss, shear force, color, volatile flavor components and taste were analyzed. Fresh (unfrozen) meat was used as control. The results showed that the moisture content of cooked UIF meat (57.81%) was significantly higher than those of cooked AF and IF meat, which was the closest to that of the control group, and the cooking loss was less than that of any other treatment group. The shear force of the UIF group was the smallest and slightly lower than that of the control group, indicating that ultrasound had a positive effect on the tenderness of cooked pork. There was no significant different in brightness between the control and UIF groups. Principal component analysis (PCA) of the electronic nose sensor responses for volatile flavor compounds showed that the first and second principal components accounted for 98.346 0% and 1.317 4% of the total variance, respectively. Linear discriminant analysis (LDA) of the electronic tongue data showed that the UIF group was not significantly differentiated from the control group and they were similar in taste, indicating that ultrasound slowed down the quality and flavor deterioration of frozen pork and brought its quality closer to that of fresh meat.