Effect of Dual-Frequency Ultrasound Combined with Citric Acid Treatment on Quality Changes of Large Yellow Croaker (Pseudosciaena crocea) during Refrigerated Storage

In order to explore the combined effects of dual-frequency ultrasound (DUS) and citric acid (CA) on the quality changes of large yellow croaker (Pseudosciaena crocea) during refrigerated storage, fresh fillet samples were treated with sterile distilled water (as a control), DUS at 20/28 kHz and 175 W, 8.0 g/L CA or DUS combined with CA (DUS + CA) for 10 min, packaged in sterile bags and stored at 4 ℃. Microbial parameters (total viable count (TVC), and psychrophilic bacterial count (PBC)), physicochemical properties (texture characteristics, color difference, pH, total volatile base nitrogen (TVB-N) content, thiobarbituric acid reaction substance (TBARS) value), water migration (water-holding capacity (WHC), low-field nuclear magnetic resonance (LF-NMR), magnetic resonance imaging (MRI)) and sensory evaluation weremeasured every two days during storage. The results showed that CA treatment could inhibit lipid oxidation and microbial growth in large yellow croaker during refrigerated storage. On the 8th day of storage, the logarithm of TVC in the control group was (8.26 ± 0.02) (lg(CFU/g)), which exceeded the spoilage limit and was significantly higher than that of the CA group (6.60 ± 0.06) (lg(CFU/g)). The TBARS value of the CA group was (0.51 ± 0.05) mg/kg on the 8th day of storage, which was significantly lower than that of the control group (P < 0.05). DUS treatment delayed the transformation of immobile water (T₂₂) into free water (T₂₃), indicating improved WHC. Overall, the quality of large yellow croaker treated with DUS + CA was better than that of all other groups during refrigerated storage. At the end of storage, the TVB-N content of the DUS + CA group was (13.79 ± 0.57) mg/100 g and its quality was the best. Collectively, we concluded that 20/28 kHz, 175 W dual-frequency ultrasound combined with 8.0 g/L citric acid treatment can significantly delay the quality deterioration of large yellow croaker, and prolong the shelf-life for at least six days during refrigerated storage compared with the control group.