Abstract: 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.

Key words: ultrasound-assisted immersion freezing; beef; freezing rate; meat quality; microstructure