| With the accelerating pace of modern life and the improvement of people’s living standard, consumers have an increasingly demanding for fresh meat and other meat quality. Frozen storage is a simple and effective way to preserve food. During the freezing and thawing process, certain changes in the quality of the meat will occur. Based on the high-voltage electrostatic field technology and its unique economic advantages in storage and preservation of meat and frozen thawed area and the ideal energy-saving effect, the thesis mainly focus on the freezing and thawing characteristics of pork and thawing laws and mechanism under high voltage electrostatic field (HVEF) to expand the relevant research. The results were as follows:(1) DSC can be used to detect the degree of protein denaturation during freezing and thawing process. At the 168 days of frozen storage time, Peak 1 denaturation enthalpy AH (J/g) of LN and-20℃ freezing were 0.25±0.02,0.13±0.06. After different frozen storage time (14 days,28 days,84 days,168 days), the microstructure by LN freezing was closest to the control (fresh state), while the ice crystals by-20℃ freezing increased with increasing frozen storage time.(2) Microwave thawing and 50℃ water thawing both have a higher thawing rate. The temperature distribution during microwave thawing is prone to be uneven, while 50℃ water thawing has a great impact on the protein denaturation in meat. Air thawing and 20℃ water thawing both have better quality indicators, but it exists some issues like microbial contamination and waste of water resources. Therefore, air thawing is chosen as the control treatment.(3) Plate electrode does not promote thawing process, delays of even. The defrosting time has accelerated markedly under corona electrode, a minimum of 1/2 of the control.-5--1℃ is the maximum ice crystals forming region, which is the most time-consuming. During HVEF thawing process temperature of meat samples changes uniformly. At different applied voltages, temperature differences between surface and center was around 0.3-1.2℃.(4) The regression model between thawing time and electric field strength was t=a1E+b1E2+ n1,and energy consumption and electric field strength was W= a2E+b2E2+n2. Compared with water and microwave thawing, the specific energy consumption of HVEF thawing was the lowest,0-190 kJ/kg, and warm water and room temperature water thawing was 248 kJ/kg and 184 kJ/kg, while microwave thawing was 1104 kJ/kg, much higher than HVEF thawing.(5) There was no significant difference in quality between HVEF thawing and the control samples. The lipid oxidation and color b* values showed a significant increase in the trend with increasing voltage, while the protein denaturation did not have similar changes. During the cold storage of meat samples thawed by HVEF, microbial growth rate was lower by 0.5-1 log CFU/g than the control. The amount of volatile basic nitrogen is also low. The distribution of muscle cells by HVEF treatment were more closely, and myofibrils were more dense.(6) At the applied voltage of 8,10 and 12 kV, the means of corona wind speed were 0.87±0.19, 1.22±0.19 and 1.49±0.13 m/s. At the applied voltage of -8,-10 and-12 kV, the means of corona wind speed were 1.01±0.12,1.24±0.17 and 1.49±0.10 m/s. As the voltage increases, the corona wind speed increases. The corona wind speed under negative voltage is larger than the positive voltage. Higher corona wind and current will promote thawing. The electric field alone does not have the promoting effect. The energy provided by the electric field is the main reason to promote thawing, and the promoting effect has certain restrictions. |
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