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 quick-frozen small yellow croakers, and to select the optimal thawing temperature. The results showed that the color difference (ΔE) and total volatile basic nitrogen (TVB-N) value of the small yellow croakers gradually increased with the increase of the temperature (2 °C, 6 °C, 10 °C, 15 °C). Compared with other thawed groups, the thawed sample of U-LT 6 °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 U-LT 6 °C thawing had the highest total sulfhydryl content (107.84 μmol/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 °C thawing can guarantee less loss in quality of the samples than other thawing methods. Meanwhile, U-LT 6 °C thawing may ensure the quality parameters of the fish by reducing the structural changes of MPs.