Abstract: This study investigated the effects of ultrasound-assisted immersion freezing (UIF) under different ultrasonic powers on the water distribution and quality of pork dumpling filler during frozen storage. The results showed that the sample subjected to UIF at 90 W ultrasonic power (UIF-90) had the best water-holding capacity, the lowest cooking loss and the greatest damage strength in the late storage period indicating that UIF-90 significantly reduced the water loss (P < 0.05) and maintained the best texture of pork dumpling filler. Compared to those treated by air freezing and immersion freezing, UIF samples had significantly lower peroxide value (POV) and thiobarbituric acid reactive substances (TBARS) value (P < 0.05), and the lowest values were observed for the UIF-90 sample, demonstrating the lowest degree of protein and fat oxidation. As the ultrasonic power increased, a* value increased first until reaching a maximum at 90 W, and then decreased for all samples (P < 0.05). According to the low-field nuclear magnetic resonance (LF-NMR) analysis, the relaxation times T21 and T22 of the UIF-90 sample were the shortest, indicating that proper ultrasonic power levels could reduce the mobility of free water and immobilized water. Therefore, UIF at an appropriate ultrasonic power can significantly improve the quality of pork dumpling filler during frozen storage, being the most effective at 90 W.

Key words: pork dumpling filler; ultrasonic-assisted immersion freezing; frozen storage; dumpling filler quality