Study On The Effect Of Freezing Technology On Heat And Mass Transfer Characteristics Of Frozen Tofu

Frozen tofu is a popular food in China.Porosity greatly affects the taste of frozen tofu,while the formation of porosity is greatly affected by freezing process.the heat and mass transfer processes occurring in tofu under different freezing process conditions,especially the latent heat release in freezing stage,phase interface migration,ice crystal growth and so on,have great influence on porosity.In this paper,the heat and mass transfer mechanism,mechanical properties and the effect of ice crystal growth on porosity and protein denaturation of tofu during freezing were analyzed.CFD software was used to simulate the temperature field of tofu under different freezing conditions.The cooling rate and porosity of tofu under different freezing conditions were studied experimentally.Finally,the optimum freezing conditions of frozen tofu were summarized.Firstly,the heat transfer mathematical model of frozen tofu is established,and the thermal physical changes caused by phase transition are considered.The ultimate stress of frozen tofu at different freezing temperature was measured by universal testing machine.The effect of low temperature on ice crystal and porosity and the effect of ice crystal growth on protein denaturation were analyzed.And then the temperature field and center temperature of frozen tofu were calculated by CFD software,which is basically consistent with the experimental results.Then the temperature field of tofu freezing process was simulated with different moisture content,different convection heat transfer coefficient and different volume.The results show that the higher the water content,the faster the freezing time,the higher the convection heat transfer coefficient,the faster the cooling rate,and the larger the volume of tofu,the longer the cooling time.Finally,the frozen tofu(cooling rate,freezing temperature,water content,tofu volume,air humidity)under various freezing conditions were analyzed experimentally.The results show that when the cooling rate is-15?-25?,the porosity of tofu with side length of 8 cm is the largest when cooling to-10.The higher the water content,the greater the porosity of tofu and the greater the air humidity.