Effects Of Ultrasound-assisted Freezing And Quick-freezing On Ice Crystal Formation And Quality Characteristics Of Sea Bass(Lateolabrax Japonicus)

Sea bass(Lateolabrax japonicus)is an important species of valuable economic fish and marine aquaculture with advantages of delicious meat and high nutritional value in China.Frozen preservation is the most effective method for sea bass to maintain a long time,and can keep its original taste and nutritional value to the greatest extent.This paper studys the quality changes of sea bass fillets during ultrasonic-assisted freezing and low-temperature quick-freezing at-18 ℃,and clarifying the freezing rate,ice crystal formation on fish meat texture characteristics,microstructure,water distribution and physical and chemical properties and structure of protein.The strategy could provide a theoretical basis for maintaining the quality of marine fish during quick freezing processing and storage.In this paper,the sea bass ice crystals processed at-20 ℃ ultrasonic assisted freezing,-40 ℃ ultrasonic assisted freezing,-20 ℃ low-temperature quick freezing and-40 ℃ low-temperature quick freezing were observed and studied.Then,the freezing substitution method and the scanning electron microscope observation method were adopted.By calculating the freezing rate,drawing the freezing curve,and observing and analyzing the ice crystal morphology,it is found that the freezing rate of-40 ℃ ultrasonic assisted freezing is the fastest compared with other freezing methods,which can produce smaller and more regular intracellular ice crystals.The muscle fibers are the most complete and arranged closely.Secondly,we systematically compared the quality changes of sea bass fillets processed by different freezing methods at-18 ℃ frozen storage under the measurement of quality indicators such as juice loss rate,texture characteristics,water distribution,microstructure,etc.The results showed that ultrasound-assisted freezing can better maintain the water retention of fish meat comparedto low-temperature quick-freezing.Moreover,ultrasonic-assisted freezing at-40 ℃ can effectively reduce the defrosting loss,cooking loss and texture deterioration of sea bass fillets,and,the water content is not easy to flow,the muscle fibers are closely arranged and have a low degree of breakage.Finally,we systematically compared the physical and chemical properties and structural changes of myofibrillar protein in seabass fillets processed by different freezing methods during-18 ℃ freezing with measuring solubility,total sulfhydryl content,Raman spectrum,endogenous fluorescence spectrum and DSC.The results showed that the solubility and total sulfhydryl content of the sample were in a downward trend,and the tightness and stability of the protein conformation were greatly reduced with the extension of freezing time.Compared with the other three groups of freezing methods,the-40 ℃ ultrasound-assisted samples had the highest solubility and total sulfhydryl content,which can effectively reduce the degree of myofibrillar protein oxidation,improving the thermal stability of fish protein and better maintaining the structure of sea bass protein.