Study On Microwave Pasteurization And Quality Variation Of Liquid Whole Egg

Traditional pasteurization approach of liquid whole egg（LWE）mainly bases on the conduction heating mode.In order to ensure that the center of pipeline reaches the pasteurization temperature,material at the pipe wall tends to be overheated,resulting in heat redundancy.High-intensity heat treatment can cause denaturation of heat-sensitive proteins and loss of nutritional components in LWE,and bring negative effects on quality.In addition,the temperature gradient orientation inside the pipeline also aggravates the occurrence of coking pipes followed by the increased difficulty of pipe-cleaning and reduced energy efficiency.As a novel physical field processing method,microwave heating can realize selective heating process without heat transfer medium by virtue of its volumetric heating principle,which can effectively solve the problems caused by traditional pasteurization approach while shortening the processing time.However,there are few studies on the microwave pasteurization of LWE,and the effects on pasteurization process and quality need to be further explored.Therefore,in this study,the rationality of microwave system was verified by constructing a multiphysics field simulation model for the continuous-flow microwave pasteurization process of LWE.The microbial lethal effect and microwave pasteurization inactivation kinetics under different power-temperature combinations were studied,and the effect of microwave pasteurization on the quality of LWE was analyzed.The main topics and results are as below:（1）Study on the heating and flow effect of LWE under continuous-flow microwave heatingThe heating effect and flow characteristics of LWE under continuous-flow microwave heating mode were investigated.The higher loss angle tangent value（tanδ=0.24）of LWE made it better to convert and absorb electromagnetic energy,obtained the higher outlet temperature and more uniform heat distribution,and realized the rapid heating process of LWE.The enhancement of microwave power increased the average outlet temperature differences between LWE and distilled water from0.66°C to 3.28°C,and the enhancement of volume flow rates reduced the temperature differences from 1.83°C to 1.15°C.In terms of flow characteristics,LWE exhibited a fluid field distribution with higher viscosity and velocity at the center and lower viscosity and velocity at the boundary,which made it have better flow and transmission characteristics in the pipeline heating process.Moreover,the temperature distribution in the pipeline and the continuous-flow heating process were also beneficial to reduce the risk of local overheating and coking pipes,which further proved the rationality of microwave heating method constructed in the study and the feasibility of continuous-flow microwave heating mode applied to the LWE processing.（2）Study on microwave pasteurization treatment of LWEMicrowave pasteurization treatment could reduce the survival populations of Escherichia coli,Salmonella enteritidis and Staphylococcus aureus by 5.854±0.072 log₁₀,6.193±0.274 log₁₀ and5.539±0.559 log₁₀.The enhancement of power density and pasteurization temperature contributed to improve the sterilization efficiency of microwave pasteurization.The performance of the nonlinear inactivation kinetic models were significantly higher than that of the first-order kinetics model.The Log-Logistic model had the highest fitting（R²:0.9984～0.9999,RMSE:0.0019～0.0720）and prediction accuracy(t_d:R²=0.9975,RMSE=0.0180;t_5d:R²=0.9990,RMSE=0.0807);while the Log-linear+Shoulder model had the worst ones(R²:0.9800～0.9992,RMSE:0.0414～0.3144;t_d:R²=0.9604,RMSE=0.1532;t_5d:R²=0.9235,RMSE=0.6917).The shouldering behavior was not obvious and a slight tailing behavior exhibited in the survival curves.Microwave power and pasteurization temperature had no significant effect on the shape and trend of the survival curves.（3）Effect of microwave pasteurization treatment on the quality characteristics of LWECompared to the raw LWE,microwave pasteurization significantly improved the foaming capacity of LWE by 5.6%～7.95%and emulsifying capacity by 0.15～0.21,the foaming stability and emulsifying stability showed obvious consistency or increasing trend compared with the raw sample.Microwave promoted the moderate unfolding of proteins in LWE,hydrophobic groups exposed and the free sulfhydryl contents increased.The secondary structure morphology changed fromβ-sheet toα-helices and disordered structures,thereby the flexibility of protein molecules increased,and the aggregation and attachment at the air/liquid interface were more easily.The absolute value of Zeta potential increased by 0.25～0.69 m V,which is conducive to maintain the stability of the system.These results proved the superiority of microwave pasteurization on improving the quality characteristics of LWE.