Influence of ultrasound-assisted immersion freezing on the freezing rate and quality of porcine longissimus muscles.

The objective of this study was to evaluate the effect of ultrasound-assisted immersion freezing (UIF) on the freezing rate and quality of porcine longissimus muscles under different ultrasound powers. UIF with a certain level of ultrasound power significantly (P>0.05) accelerated the freezing rate. The phase transition times of samples treated with UIF at 180W (UIF-180) were the shortest. There were no significant differences (P>0.05) in a* (redness), b* (yellowness), pH values or cooking loss among UIF, IF, and control (fresh muscle) samples. Investigation of the microstructure of frozen muscles demonstrated that UIF-180 remarkably reduced the size of ice crystals and made their distribution more uniform. UIF-180 samples showed a significant (P<0.05) reduction in thawing loss and T21 and T22 relaxation times compared with other treatments, which meant that UIF at certain powers could reduce the mobility and loss of immobilized and free water. The results showed that UIF at certain powers significantly increased the freezing rate of muscle samples and improved meat quality.