Preservation Mechanism And Experimental Research On Electromagnetism Treatment Of Low Temperature For Postharvest Fruit And Vegetable

Nutritional value and security quality of the fresh fruit and vegetable,as one of the daily necessary food of life,are closely related to the people?s level of the health.Due to sensonal and regional differences and high moisture content of the fruit and vegetable,it is very easy to decay.Therefore,it is significant to develop a novel food preservation method so as to further prolong the shelf life and improve the preservation quality.In this paper,a method combining the theoretical analysis and experimental research was applied to explore coupling effect of temperature field and electromagnetic field treatment on fruit and vegetable.The preservation mechanism on electromagnetism treatment of low temperature for postharvest fruit and vegetable was deeply studied and analyzed in aspects of characteristic of heat and mass transfer,chilling injury and freezing injury,comprehensive assessment of physiology and biochemistry parameters.It provided theoretical support and laid the foundation for the optimal process of the electromagnetism treatment.1,Based on the biological and thermal effects of the electromagnetic field,we made mechanism analysis and experimental research about effects of electromagnetic field on the specific heat,convective heat transfer coefficient and internal heat source during precooling and diffusion coefficient of mass transfer during cold storage.Mathematical models of heat transfer about cylindrical and spherical fruit and vegetable were established by using the numerical simulation of COMSOL Multiphysics.Experiamntal results confirmed that mathematical models of heat transfer had high precision.The uniform static magnetic field of magnetic flux density(40Gs)had a positive influence on improving the hydrocooling rate of the cucumber and cherry tomato.2,Freezing and refrigerated storage system and electromagnetism of low temperature hydrocooling treatment system were built by principles of refrigeration and high-precision control of siemens PLC.Experiment results confirmed that two systems could meet the requirement of high-precision process technology.And it could provide a basic condition for the research of heat and mass transfer during precooling and chilling(freezing)injury during cold storage.3,Based on the theory of cold and heat shock treatment on fruit and vegetable,the temperature jump treatment method combining cold and heat shock treatment was developed.And the effects of different direction of temperature jump treatment on the preservation quality of cucumbers were researched.Experimental results showed that temperature jump treatment treatment of appropriate intensity(CHT)could integrate the respective advantages of cold and heat shock to further improve resistance abilities.With the temperature jump treatment of negative direction(HCT),the damage of thermal stress could produce harmful effects on preservation quality.4,Hydrocooling technology of electromagnetic treatment of low temperature was studied and optimized by the central composite design(CCD)using the cucumber as the sample materials.The response surface model was estabulished using the representative sensory quality and physicochemical parameters as response values.Furthermore,the optimal treatment parameters were optimized according to comprehensive evaluation of the response values.Experiment confirmed that this model had high prediction precision and results showed that the electromagnetic hydrocooling pretreatment(temperature of the water was 2 ~oC,magnetic flux density was 70 Gs and treatment time was 40 min)had a positive effect on improving the preservation quality.5,Based on the biological effect and weak thermal effect of low frequency alternating magnetic field,effects of continuous and intermittent alternating magnetic field(20 Gs,60 Hz)on chilling and freezing injury damage were studied during low temperature storage of the banana and grape.Experimental results showed that the continuous alternating magnetic field treatment producing continuous thermal effect was better than intermittent alternating magnetic field treatment in the aspect of inhibiting the banana chilling injury.Appropriate alternating magnetic field could increase the degree of supercooling of grape?s tissue fluid and reduce the latent heat of phase change,which could lower freezing injury probability under freezing-point storage of the grape.