Simulation Of Canned Food Sterilization And Development Of Automatic Correction System

Canned food is an important part of the food industry.Thermal sterilization inactivates microorganisms that cause food spoilage at high temperatures to achieve food commercial sterility,which is an important part of canned food processing.However,in the practical process,determining the location of the cold spot and monitoring the real-time temperature of the cold spot are difficult,the temperature distribution of the thermal sterilization equipment is uneven,and the actual temperature of the sterilization retort deviates from the set value.Therefore,the temperature and the lethality of the cold spot inside the food cannot be accurately measured,and the thermal sterilization process cannot be precisely controlled,resulting in reduction of food quality and waste of resources.Regarding the issue above,models of canned food including the headspace and the horizontal high-temperature sterilization equipment were constructed using the COMOL Multiphysics software,the prediction model of cold spot temperature and lethality of food was established and optimized,and the lethality prediction and automatic correction system was developed.The main results of the research are as follows:1.A two-dimensional axisymmetric model of liquid canned food,considering the effect of headspace was constructed.The thermal penetration experiment of water and1.0% CMC solution verified the model can more accurately reflects the temperature change during thermal sterilization than the model without top gap(the mean relative errors of temperature are 1.92% and 2.55%).The velocity field,temperature field and lethality field in the can simulated by different models were compared,indicating the head gap cannot be ignored.Pressure changes were also analyzed.The smaller the headspace and the higher the holding temperature results in the greater pressure,which provides a reference for determining the control pressure of the retort.2.A three-dimensional symmetrical model of the static horizontal high-temperature sterilization retort was established.The physical changes in the heating section during the thermal sterilization process in the full spray and steam modes were simulated.The simulated values of temperature at different positions in the sterilizer were compared with the experimental ones by thermal distribution test.In the full spray mode,the RMSE of temperature was 1.97?.In the steam mode,the RMSE values in the cooling and linear heating sections were 1.36? and 0.86?,which verifies the accuracy of the model.The simulation results show that the slowest heating zone of the retort is located at the first layer near the central axis in the full spray mode,while in the steam mode,the SHZ is located at the bottom near the outer wall.The simulation also shows that the cold spot in the food is not at the center of the can,but offsets to the cooler surface side.3.Based on the idea of transfer function,the complex thermodynamic parameters were simplified into temperature change factor k and hysteresis factor j,and a mathematical model for predicting the cold temperature of food and calculating the lethality(F value)from the temperature of the sterilizer is established.Thermal penetration tests were performed on bagged and metal canned meat,metal canned eight-treasure porridge,glass bottled and metal canned 1.0% and 2.0% CMC solutions by F-value probe.The deviation of F value at cold spot were all within 1.13%,which indicates that the model is suitable for foods with different heat transfer properties and different packaging methods.The calculation steps of k and j was simplified by combining CFD simulation,the error between the F value predicted by this method and the measured value is also within 3.42%,which can avoid multiple thermal penetration experiments.4.A lethality prediction and automatic correction system that can be used on automated thermal sterilization equipment was developed by using single-chip microcomputer.The lethality tester was inserted into the bagged luncheon meat,and the temperature tendency of cold spot and cumulative F value curve were compared to verify the system can accurately predict and display the cold spot temperature and lethality in real time.The wireless thermal tester was placed in 1.0% CMC solution packed in metal can,and the temperature deviations from the set value are artificially produced in the early,middle,late and multiple times of the insulation.The verification shows that the system can automatically perform the correction operation,to ensure the lethality larger than the set value.The system is highly portable and can be maintained and monitored through software.