Experimental And Simulation Study On Pork Quality By Vacuum Thawing

Pork is the main type of meat consumption in China.Appropriate freezing and thawing methods are the key to ensure good meat quality.Vacuum thawing method has the advantages of fast thawing speed,good product quality after thawing,and little loss of nutrients and quality.As a new thawing method,it gradually attracts attention in the field of thawing.However,at present,there are few studies on vacuum thawing,and the research field is also at a higher pressure level.There has not been a systematic study on frozen pork and its quality after thawing.Therefore,this study uses pork as raw material,and the traditional air thawing method as the control group(15 ? air thawing).The freezing rate,thawing rate,and the water retention(thawing loss rate,cooking loss rate,pH value,conductivity),texture(hardness,elasticity,chewiness,cohesiveness,adhesiveness,resilience)of pork after thawing were used as detection indicators.The effects of different thawing methods,pressure and temperature on the thawing effect of pork were studied.Since vacuum thawing process is a complex process including phase transition and air flow,the heat transfer and steam condensation models in the vacuum thawing process of pork were established,including geometric model,the determination of the physical parameters of the mathematical model,etc.Finally,the coupling of multi-physics was discussed,and the simulation process was completed in COMSOL software.The main research contents and conclusions are as follows:(1)Set up and debug the instruments of the vacuum thawing test bench,so that the pressure and temperature values during the test can meet the requirements of the experimental setting and ensure the smooth progress of the experiment.(2)Finite element analysis software COMSOL was used to carry out numerical simulation analysis on heat transfer and condensation mechanism during vacuum thawing of pork.Due to the strong bi-directional coupling between temperature field and humidity field in the process,the heat transfer model and the calculation of flow field are separated in this paper.First,geometric and mathematical modeling of the temperature field of the meat piece was carried out.In the simulation process,the sensible heat capacity method was used to process the latent heat release in this temperature range,and the reliability of the model was verified by comparison with the experimental results.Secondly,the humidity and temperature during steam condensation were simulated,and the heat flux of steam condensation and heat conduction during the thawing process were calculated.It plays a certain role in understanding the thawing mechanism and quantitative estimation of the vacuum thawing process.(3)Quality testing on the samples after vacuum thawing under different freezing methods,thawing pressure,and thawing temperature conditions was carried out.The water retention of the thawing pork was judged by the thawing loss rate,cooking loss rate and pH value after thawing.The texture of pork was evaluated by measuring the hardness,elasticity,and chewiness of the sample.The results show that: among the samples processed by different freezing methods,the samples after-35 ? immersion and air cooling have lower,thawing loss rate and cooking loss rate,respectively: 1.4%,4.53% and 1.44,5.00 %,There is no significant difference between pH and electrical conductivity(p> 0.05),and the texture properties are good.Comparing different thawing pressures,it was found that the thawing time was shortest when the thawing pressure was 100 Pa,which was 8.83 H,while the thawing loss rate and cooking loss were the lowest,which were 1.45% and 5.36%,respectively.The pH value was 6.41,the texture indexes were good,and had high hardness,elastic chewiness,etc.Judging from the effect of different temperatures on the vacuum thawing of pork,the shortest thawing time is 8.67 h at a temperature of 20 ?,but the quality test of the thawing samples showed that the thawing loss rate at 15 ? was 1.44%,the loss rate was 5.48%,and the texture properties of the samples treated below 10 ? and 20 ? were also the best among the three groups.It can be seen that vacuum thawing at 15 ? can guarantee the quality of the sample.Therefore,frozen pork stored at-35 ? can be thawed in vacuum at 15 ? and 100 Pa pressure,which can guarantee the quality of pork to the greatest extent while having a faster thawing rate.