Effect of osmosis treatment on meat quality and myofibrillar protein of freeze-dried tilapia

In order to explore the effect of osmotic treatment on improving the freeze-drying efficiency of tilapia meat and the quality of dried products after rehydration, and to provide theoretical supports for the development of freeze-dried tilapia meat products, we pretreated the tilapia meat with salt, propylene glycol and compound penetrant (Salt+propylene glycol), followed by blanching and freeze-drying. Then we analyzed the effects of penetrant pretreatment on the cooking loss, freeze-drying characteristics, rehydration rate and myofibrillar protein characteristics of tilapia meat. The results show that salt, propylene glycol and composite penetrant could reduce the cooking loss and improve the drying efficiency of tilapia meat. The freeze-drying time of composite osmotic treatment was the shortest (19 h), and the drying time of fish after the salt and propylene glycol osmotic treatment was 20 h, which was significantly shorter than that of the control group (24 h). The propylene glycol and composite penetrant improved the rehydration of dried fish significantly (P<0.05), and the rehydration rate of dried fish treated with propylene glycol was the highest (71.11%), which was significantly higher than that of the control group (P<0.05). Salt penetration had a significant effect on the texture of dried fish after rehydration (P<0.05), among which hardness and elasticity had the greatest effects (94.3±3.9) g and (3.44±0.23) mm, respectively. Propylene glycol had no significant effects on the hardness of fish, but could improve the elasticity. The addition of salt accelerated the oxidation of myofibrillar protein, and the contents of myofibrillar protein and sulfhydryl decreased 0.32 mg·mL⁻¹ and 0.47 μmol·g⁻¹, respectively, while the surface hydrophobicity and carbonyl content increased 4.10 μg and 0.23 nmol·mg ⁻¹, respectively. SDS-PAGE shows that the myosin heavy chain band disappeared. Propylene glycol osmotic protective agent slowed down the formation of ice crystals and inhibited the protein oxidation during pre-freezing. The mass concentrations of ionic bond and hydrogen bond increased by 0.65 mg·mL⁻¹ and 0.33 mg·mL⁻¹, respectively, the mass concentration of disulfide bond decreased (P<0.05), which improved the protein stability. Therefore, the compound penetrant can inhibit the protein oxidation effectively during the processing process and keep good taste of dried fish after rehydration, which is suitable for the pretreatment of tilapia before vacuum freeze-drying.