Adiabatic Compression Heating Of Selected Materials And The Sterilization Effect Of Milk During High Pressure Assisted Thermal Processing

During the high pressure processing, pressurization is always accompanied by temperature increasing in the production due to compression of the materials. This can result in non-uniform temperature distribution during processing. The different of temperature profiles within the high-pressure vessel would likely impact on the effect of this processing. Moreover, the compression heating behavior can also influence the inactivation of bacteria, spore and enzyme. It is necessary to study the adiabatic compression heating of different materials under combined pressure and temperature conditions as well as its effect on sterilization during the high pressure assisted thermal processing. Therefore, the adiabatic compression heating must be taken into consideration so that sterilization technology and conditions can be controlled accurately.The main research contents and results are as follows:1. The effect of pressure, initial temperature and composition of different materials on the adiabatic compression heating was studied. The adiabatic compression heating of ethanol and fatty food increased with increasing pressure, while the adiabatic compression heating of the other test materials were slightly affected by the pressure. For foods with high water content, the adiabatic compression heating increased with increasing initial temperature. The effect of initial temperature on the adiabatic compression heating for soybean oil is not significantly. Among the food products tested, the ethanol resulted in a higher temperature rise compare to those foods with high water content.2. A empirical equation of adiabatic compression heating based on pressure and temperature was established. The second-order polynomial was used to fit the adiabatic compression heating of whole milk, soybean oil, honey, orange juice, etc. The regression coefficients of these equations were all above 0.95. The verification test of this equation demonstrated the relative error were less than 4.6%. So, the equation had good predictability.3. The sterilization effect in milk under high pressure assisted thermal processing was studied. The effect of the adiabatic compression heating could not be ignored during the high pressure assisted thermal processing. Under the appropriate initial temperature condition, the sterilization effect of the high pressure assisted thermal processing was superior to corresponding thermal treatment. It is beneficial to improve the sterilization effect by increasing the pressure or initial temperature.4. The effect of pressure, temperature and pressure holding time on the inactivation were studied. The gray correlation method was used to discuss the factors during the high pressure assisted thermal processing. The relational order were:pressure holding time>temperature>pressure.