| The effect of high voltage electrostatic field(HVEF)combined with modified atmosphere packaging(MAP)and controlled freezing-point storage(CFS) on the quality of Tilapia fillets were studied, explore the best conditions for high voltage electrostatic that can extend the quality of fresh tilapia fillets,and study the traditional physical and chemical indicators, protein biochemistry, protein degradation, protease activity and muscle microstructure as well as the specific spoilage organisms on tilapia fillets in HVEF treatment, discuss HVEF impact on quality of tilapia fillets, for application of HVEF in tilapia product, providing the basic theory basis for tilapia fillets preservation methods,promote tilapia fillets preservation technology.The main research and conclusions are as follows:1. Optimal MAP and CPS conditions for Tilapia fillet.Tilapia fillets packaged with different inflatable V/W ratios and controlled atmosphere with 100%CO2, 70%CO2/30%N2, 50%CO2/50%N2 and 30%CO2/70%N2 are stored respectively at freezing-point, the shelf life of Tilapia fillets was evaluated by the sensory evaluations as well as key indexes such as drip loss and chromatic aberration, microbial changes and TVB-N. Results showed that the V/W=3:1 was one of the optimal modified atmosphere packaging technology factor. Due to the high concentration of CO2 would accelerate the drip loss, the modified atmosphere at the level of 70%CO2/30%N2 was the other optimal factor which can protect the Tilapia fillet effectively as well as keep their good appearance.2. The effect of different Voltage of HVEF on the quality of Tilapia filletsThe effect of different Voltage of HVEF on the quality of Tilapia fillets was studied,analyses and compares of 3.8 k V, 1.8 k V HVEF on the influence of tilapia meat quality indexes. The results shown that the HVEF can significantly inhibit corruption and badsmell of fillets, slow down the fish muscle elasticity and sensory quality decline, can also obviously improve the drip loss effect, but had no significant effect on fish color; HVEF also effect on the microbial proliferation, combining MPA technology, the shelf life of tilapia fillets can reach 30 d, the sample without peculiar smell, better than control group to extend the time for nearly 9d. In this study, 3.8 k V HVEF effect is better than 1.8 k V. With the extension of cold storage time, the obvious changes in fish muscle tissue structure,characterized by muscle fibers occurred fracture and small pieces, muscle fiber area ratio significantly reduced, sarcomere clearance and the clearance area ratio increases significantly, muscle fibers by dense structure become loose. HVEF can slightly inhibit muscle fiber fracture, but for the integrity of the muscle tissue structure effect is not obvious. Cell integrity and muscle fiber was observed by electron microscope, the cellular structure is complete, intercellular adhesion are close, proven that muscle protein degradation were depressed.3. The changes of protein degradation and biochemical characteristics during storageComparison of biochemical indicators of tilapia fillets and SDS-PAGE electrophoresis were assayed, the study found that with the extension of storage time, the salt soluble,total sulfhydryl content, Ca2+-ATPase activity of actomyosin of the two groups showed a declined tendency in general, but the surface hydrophobicity showed an up trend.After24 days of the preservation, the salt soluble drop of the actomyosin treated by the 3.8k V HVEF has dropped down 63.98%, rate of descent is 2.368 mg/g by day, and the control group dropped down 79.37%.The total sulfhydryl content of the actomyosin treated by the3.8k V HVEF has dropped down 58.48%, and the control group dropped down 68.91%.The Ca2+-ATPase activity of the actomyosin treated by the 3.8k V HVEF has dropped down37.22%, and the control group dropped extremely down 72.07%.The surface hydrophobicity of the actomyosin treated by the 3.8k V HVEF has increased 1.86 times, and the control group increased 2.55 times. SDS-PAGE electrophoresis showed that under the condition, myosin heavy chain changes slowly, strip light density greater, lower degree of muscle protein degradation in storage process, can better inhibit protein denaturation.Above all, HVEF has the positive effect to the shell life of tilapia fillets.4. The effect of high voltage electrostatic field on CathepsinThe analysis of Cathepsin B, L, H and D activity were assayed, tried to analyze effects of 3.8kv HVEF. The results shown that the HVEF combined with MAP and CFS on cathepsin B and L activity are significant, and less influence on activity of Cathepsin H, D;Cathepsin B activity in the process of storage are upward, Cathepsin L activity rise firstthen drop, activity of Cathepsin H, D haven’t shown the regular changes.5. Microflora analysis and specific spoilage organisms(SSO) identification under the HVEF.The SSO identification were investigated by PCR(polymerase chain reaction)-DGGE(denaturing gradient gel electrophoresis) analysis. The total bacteria DNA of three different batches fillets were extracted for the identification. Six types of bacteria were identified by DNA sequence and analyzed form main bands on the DGGE profiles in three different samples. Those bacteria were closely related to Carnobacterium, Lactobacillus,Lactococcus, Streptococcus, Clostridium and Pseudomonas. Lactic acid bacteria(LAB)Carnobacterium.sp was assumed to be the dominant microorganisms in this specific preservation condition. Carnobacterium.sp were reinoculated to the fillets in order to study the microbial effect on the Tilapia fillets. Results showed that Na Cl concentration range of0~10%(inhibited at 8%), p H 8.0(inhibited at 4.0) and 28℃ were the optimal growth conditions for the Carnobacterium.sp.The combination of HVEF, MAP and CFS technique can maintain the quality of the tilapia fillet. Its shelf life has also been effectively extended, the new kind of preservation method for tilapia fillets products will provides a feasible technical solution in the domestic supermarket circulation. |
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