Effects Of Freezing Storage Period And Temperature Fluctuation On The Quality Of Penaeus Vannamei

According to the traditional 3T（Time,Temperature,Tolerance）theory,the tolerance of frozen products during frozen storage is closely related to temperature and time.When there are high-frequency temperature fluctuations in the frozen storage environment,the 3T theory will fail.Therefore,studying the impact of temperature fluctuations on the quality of frozen products is of great significance.South American white shrimp,as a highly nutritious seafood with a huge market,relies on the cold chain for circulation during the import and export process,and there are high-frequency temperature fluctuations in many links of the cold chain circulation process.Temperature fluctuations can lead to the growth of ice crystals,protein denaturation,lipid oxidation,color change,and weakened water holding capacity,thereby affecting the quality of frozen South Tibetan white shrimp.In summary,studying the quality changes and shelf life prediction model of South American white shrimp under temperature fluctuations can provide a theoretical basis for quality monitoring and shelf life prediction of South American white shrimp during cold chain circulation,and also supplement the failure of 3T theory under high-frequency temperature fluctuations.A total of 5 temperature fluctuation groups and a control group of-40°C were established,including-18±0.5°C、-18±2°C、-18±4°C、-18±6°C and-18±8°C,respectively.Fresh South American white shrimp died suddenly in ice water and were placed in freezers of different experimental groups in two states:whole shrimp with shell and shellless shrimp,to study the impact of different temperature fluctuations on the quality of frozen South American white shrimp.Freeze South American white shrimp in freezers of different experimental groups for 120 days,and conduct tests every 30 days to test the TVB-N（volatile base nitrogen）value,TBARS（thiobarbituric acid reactant）value,L^*（brightness）value,a^*（red green）value,b^*（yellow blue）value,hardness,elasticity,chewability,resilience,water holding capacity,p H（acidity）value,and other indicators of South American white shrimp.Using-40°C as the control group,compare and analyze the effects of different temperature fluctuations on the quality of frozen South Tibetan white shrimp.During the frozen storage process,the L^*,a^*,and b^*values of South American white shrimp gradually increase,and the sample brightness gradually increases,leaning towards red and yellow.The smaller the temperature fluctuation in the freezer,the smaller the color difference of frozen South American white shrimp,which is closer to the color difference value of the control group;The TVB-N value gradually increases over time.When frozen for120 days,the TVB-N value of the whole shrimp frozen in a shell state in the-18±8°C group freezer increased to 32.01 mg/100 g,which exceeded the national standard and was not edible.The frozen South American white shrimp in other temperature fluctuation groups did not meet the national standard;The TBARS value also gradually increased over time.When frozen for 120 days,the TBARS value of the whole shrimp frozen in the shell state in the freezer of the-18±0.5°C、-18±2°C、-18±4°C、-18±6°C and-18±8°C groups increased by 600%,625%,683%,725%,and 883%,respectively.The TBARS value of the control group increased by 583%.The increase in temperature fluctuations accelerated the TBARS value growth of the frozen samples,exacerbating the degree of lipid oxidation;The texture indicators such as hardness,elasticity,chewiness,and resilience showed a downward trend,and the greater the temperature fluctuation,the faster the decline rate of each texture indicator,and the greater the difference compared to the control group;The water holding capacity gradually decreases,and the contents of free water,bound water,and non flowing water all continue to decrease.The larger the temperature fluctuation,the more obvious the decrease in water holding capacity.Overall,when frozen at-40°C,the deterioration degree of various physical and chemical indicators of South American white shrimp is the smallest.Compared to other temperature fluctuation groups,the quality of South American white shrimp frozen at-18±0.5°C is closest to that of the-40°C group.It can be seen that reducing temperature fluctuations helps to inhibit the growth of ice crystals in the muscle tissue of frozen Tibetan white shrimp,reduce the damage of ice crystals to muscle fiber structure,reduce protein denaturation and lipid oxidation,and slow down the rate of deterioration.Moreover,when frozen in the shrimp shell state,the temperature fluctuation has a relatively small impact on the storage of South American white shrimp,and the deterioration rate of various physicochemical indicators is slower compared to the whole shrimp state,which is more conducive to its preservation.After measuring the changes in physical and chemical indicators of South American white shrimp during 120 days of frozen storage,based on the Pearson correlation coefficient between various physical and chemical indicators,TVB-N values with Pearson correlation coefficients greater than 0.9 were selected as key indicators for shelf life prediction models;Establish a curve for the key indicator factor-temperature fluctuation,and obtain the pre index factor A₀ and activation energy R_a;Establish the TVB-N Arrhenius formula based on the pre exponential factor A₀ and activation energy R_a;Substitute the TVB-N Arrhenius formula into the first-order kinetic model to obtain Arrhenius shelf life prediction models under different temperature fluctuations.Studying the impact of different temperature fluctuations on the quality of frozen South American white shrimp meat is of great significance for quantitatively describing the rate of quality decline of South American white shrimp under temperature fluctuations,and seeking a balance between extending the high-quality storage period and maintaining resources to reduce temperature fluctuations.Study the effect of shrimp shells on the frozen storage quality of South American white shrimp,and explore more suitable frozen storage methods for fresh South American white shrimp.The calculated Arrhenius shelf life prediction model provides a theoretical basis for quality monitoring and shelf life prediction of South American white shrimp during cold chain circulation.