Effect Of Ultra-high Pressure Treatment On Preservation Of Freshwater Fish During Refrigerated Storage

China is the most important aquatic products country in the world, the total output of aquatic products is rank first in the world. Freshwater fish is the main cultured aquaculture species in China. Grass carp ranked first among freshwater fish with a production estimated to be 5376800 tons in China in 2014. Because of the freshwater fishery production of seasonal is strong, aquatic products are easy to spoilage, therefore it is particularly important to retain aquatic products freshness. Usually people use low temperature cold storage and frozen storage to prolong their shelf life. But this method of low temperature preservation storage period is short, frozen storage is bad for quality.At present, the research focus of high pressure processing technology concentrated on seawater fish sterilization, protein modification, gel characteristics, meanwhile the influence of high pressure processing treatment on fresh water fish quality is not too much. So this research use freshwater fish species grass carp as the main research object, analysis different strength of ultra-high pressure and cold storage time impact on preservation of freshwater fish.To study the influences of ultra-high pressure processing on microbes of grass carp fillets, by determining the aerobic bacterial count and psychrophilic bacteria amount used different pressure strength and cold storage time on grass carp fillets, results show that single from the perspective of psychrophilic bacteria, more than 300 MPa can extend the storage period of 15 days. Single from the point of the aerobic bacterial count, 300-400 MPa of ultra-high pressure processing can extend the storage period of 12 days, 500-600 MPa of ultra-high pressure processing can be extended for 15 days.To study the effect of ultra-high pressure processing on mainly protease enzyme activitiy grass carp fillets, by determined six kinds of protease enzyme activity using different pressure strength and cold storage time of grass carp fillets, the results show that more than 200 MPa ultra-high pressure treatment can significantly inhibit the enzyme activity of Calpain and MBSP. More than 300 MPa ultra-high pressure treatment can significantly inhibit the enzyme activity of Cathepsin B, Cathepsin L, Collagenase.On the basis of ultra-high pressure on sterilization and enzyme, we use ultra-high pressure to prolong freshwater fish fresh during cold storage. By determined physical and chemical, protein degradation, protein structure index of grass carp fillets, insight into the different strength of ultra-high pressure processing and cold storage time on quality of grass carp fillets.(1) Changes in physicochemical indexes of grass carp fillets during storage were studied by measuring p H, TBARS, texture and other indicators. The results show that with the extension of storage time, a series of changes have taken place in the quality of the grass carp fillets: compared with the control samples, L* value was significantly increased after HPP, color deterioration occurred. the hardness of grass carp fillets increase. Drip loss of grass carp increased with increasing storage time, water holding capacity showed a trend of decline, but after ultra-high pressure processing, Drip loss of samples were less than the control group, water holding capacity were greater than the control group, ultra-high pressure can alleviate the worse trend of water retention ability. For sensory evaluation index, ultra-high pressure treatment group is better than the control group.(2) Changes in protein degradation indexes of grass carp fillets during storage were studied by determining SDS-PAGE, amino nitrogen content, TCA-soluble peptide content. The results show that with the pressure increased, TCA-soluble peptide content and amino nitrogen content showed a trend of decline, the content of samples were smaller than the control group after ultra-high pressure. SDS-PAGE shows that the ultra-high pressure after the myofibril protein in a certain degree of degradation, muscle, plasma protein in a certain degree of degeneration. Myofibril protein has a certain degree of degradation, Sarcoplasmic protein has a certain degree of degeneration. With the extension of time, the control group in protein degradation is serious, ultra-high pressure effectively slowed the degree of degradation, which has good effect on quality.(3) Changes in protein structure indexes of grass carp fillets were studied by determining a variety of means like total sulfhydryl content, active sulfhydryl content endogenous fluorescent spectrometry and Raman spectroscopy, the results show that with the increase of pressure, Ca2+-ATPase activity and total sulfhydryl content decreased significantly, active sulfhydryl content to increase after the first down. Endogenous fluorescence and Raman spectra show that the high pressure processing changed the secondary and tertiary of myofibril protein structure, leading to protein denaturation. On total, this change is good for quality.