Effect of ultrasonic thawing temperature on the quality of quick-frozen small yellow croaker (Larimichthys polyactis) and its possible mechanisms

Thawing temperature is an important factor affecting the thawing quality characteristics of quick-frozen small yellow croakers. The objective of this study was to reveal the effect of ultrasonic-assisted low-temperature (U-LT) thawing on the physicochemical quality and structural characteristics of myofibrillar protein (MPs) of quickfrozen small yellow croakers, and to select the optimal thawing temperature. The results showed that the color difference (Delta E) and total volatile basic nitrogen (TVB-N) value of the small yellow croakers gradually increased with the increase of the temperature (2 degrees C, 6 degrees C, 10 degrees C, 15 degrees C). Compared with other thawed groups, the thawed sample of U-LT 6 degrees C (20 kHz, 50 W/L) had the lowest thawing loss (5.44%), cooking loss (7.87%), and thiobarbituric acid-reactive substance (TBARS) value (0.24 mg MDA/kg). Moreover, the MPs obtained by ULT 6 degrees C thawing had the highest total sulfhydryl content (107.84 mu mol/g protein) and free amino content (275.27 mmol/g), and the proportion of secondary structure was closest to the fresh sample. Therefore, U-LT 6 degrees C thawing can guarantee less loss in quality of the samples than other thawing methods. Meanwhile, U-LT 6 degrees C thawing may ensure the quality parameters of the fish by reducing the structural changes of MPs.