Study On The Effect Of Shelf Life Storage On Quality Of Chilled Modulated Fish

In recent years,with the change of national consumption habit and the improvement of living standards,the development of chilled prepared foods has also been very rapid,especially in freshwater fish products in China.However,most of chilled prepared fish products are packaged directly for sale after slaughtered and cleaned,now,and did not take any fresh-keeping measures.Therefore,the development of effective preservation methods which make chilled prepared fish products maintain the better taste in the shelf life has a great significance.Meantime preservation methods have a great significance for enhancing the quality as well as adding value of the product and improving satisfaction of consumer.The mechanism of chilled prepared fish deterioration after cooked with the extension of refrigeration time must be clear.The subject in this thesis was mandarin fish,which is one of the high value freshwater fish.The mechanism that the texture deterioration of cooked fish products,due to the prolonging the storage time was studied,from two perspectives of the storage process and heating process.The changes of fish meat quality,the changes of protein structure and the migration of water,and protein degradation during storage were mainly discussed.Finally,the changes of protein structure,the interaction of protein and water,protein degradation and oxidation during heating process were discussed.The main research contents are as follows:1.The quality change and basic physical and chemical properties of mandarin fish in cold storage were analyzed.The TVBN value of fish meat was 20.49 ± 0.55 on the fourth day,which reached the standard of corruption of GB 2733-2015 Health Standards for Fresh-frozen Animal Aquatic Products.Therefore,the shelf life of the fish was 4 days.At the same time,the change of pH also exceeded 0.2 on day 5,consistent with the TVBN results.During storage,the texture quality index of mandarin fish changed significantly,and the hardness,elasticity,adhesiveness and chewiness showed a shape decreasing trend.There was no obvious change in the moisture content of fish meat,and the cooking loss and the centrifugal loss increased during the storage period,indicating a significant decrease in water holding capacity and the quality of fish meat.The surface hydrophobicity of myofibrillar protein in fish increased,the total sulfhydryl and active sulfhydryl groups showed a downward trend.Suggesting that the structure of the protein has changed during storage.2.The protein degradation of mandarin fish in cold storage was analyzed.In theprocess of storage,the content of soluble peptide in TCA gradually increased,indicating that the protein was degraded.By SDS-PAGE electrophoresis,there was no significant change in the main electrophoresis bands,suggesting that some low-abundance proteins may be degraded.Then the whole protein was analyzed using quantitative proteomics techniques.Tropomyosin and actin,which are related to texture quality,are screened,both of which are the major components of myofibril filaments.It can be obtained during the storage of mandarin fish,myofibril filaments structure changes have an important role on the quality of fish.Finally,protein immunization(WB)was used to verify the changes of tropomyosin content.The changes in the content of desmin,which play an important role in fish quality,were also examined.It is confirmed that tropomyosin and desmin can be used as an indicator of the quality of fish.3.The change of protein structure of fish and the interaction of protein and water in the refrigerated storage were analyzed.Using low-field nuclear magnetic resonance(LF-NMR)to study the changes of water migration during the storage of fish,the correlation analysis showed that the decline of immobilised water content and the liquidity were positively correlated with the deterioration of fish meat quality.Meantime the content of immobilised water accounts for more than 95% of the total water of fish.This shows that the change of water has a direct impact on the quality of fish.The decrease of the hydrogen bond content of the protein molecules leads to the decrease of the bound water content in the fish meat.The change of immobilised water is mainly attributed to hydrophobic interactions and disulfide bonds which made the protein network.The structure of the mandarin fish protein was changed during storage.As a result of Raman spectroscopy,?-helices in the protein secondary structure ware transformed into ?-sheets and irregularly curled;the content of disulfide bonds is increased and the conformation is changed;the tryptophan,tyrosine and aliphatic amino acid residues are exposed,protein microenvironmen was changed,hydrophobic interaction enhanced.4.The changes of texture quality and protein during the heating process of mandarin fish were analyzed.The texture index of fish had a significant change after heating,and the changes of hardness,elasticity,gum stickiness and chewiness were consistent with those of raw meat,indicating that the change of raw fish had an important influence on the quality of cooked fish;The quality of cooked fish is inferior to that of raw fish,which may be due to protein changes in the fish duringheating.The water migration was analyzed by LF-NMR.Changes in moisture content and fluidity during storage are basically the same as those of raw fish meat.The content and liquidity of immobilised water are related to the deterioration of fish meat quality.The content of immobilised water in cooked fish is obviously lower than that of raw fish.This may be one of the reasons for the deterioration of fish quality after heating.Then,using of DSC technology to determine the process of protein denaturation during heating,set the heating time gradient.By electrophoretic analysis,the protein did not degrade during heating.Raman spectroscopy was used to further analyze the change of ?-helix during heating.The content of ?-helix decreased gradually during heating,indicating that the change of protein structure may also be one of the reasons of the quality deterioration after heating.The changes of the hydrogen bonding content showed a positive correlation with the ?-helix,indicating the influence on the protein texture quality.Hydrophobic interactions and disulfide bonds on the protein network may affect both the protein structure and the migration of immobilised water,thus,affecting fish quality.Finally,further studies on protein oxidative aggregation.Protein carbonyl content increases with storage and heating time,indicating that the protein is oxidized.Protein sulfhydryl content gradually decreased,indicating that the protein sulfhydryl gradually oxidized disulfide bond;dimer tyrosine content gradually increased,indicating that protein tyrosine oxidation complex.