| The heat treatment of milk is an important part of traditional soybean food production. High temperature steam produced by coal-fired boilers is used as a heating source. The use of coal-fired boiler will be restricted because of policy of energy-saving. Ohmic heating technology, which is considered as the most powerful potential heat technology, has many advantages such as uniform heating, no heat transfering face, easy controlling and environmental protection. Although the corresponding research of ohmic heating technology for food is in progress at home and abroad, the influence of the mechanism of ohmic heating on soybean milk quality has not been reported.This paper is based on multidisciplinary theory including Physics, Electromagnetics, Food Matter, Chemical Engineering, Electrostatic technology, testing technology and so on. It mainly carries out the reaserch work of2phases. Fast, continuous ohmic heating device of liquid food is designed and manufactured, and the key problem, electrode pollution, which constrains the development of the ohmic heating technology, has been solved. Secondly, related experiments on the part of the physical and chemical characteristics of soybean milk have been made, using self-developed device. Main characters of ohmic heating on soybean milk have been expounded. Pollution of electrode is developed, and the best ohmic heating condition is designed.Main contents of the paper are shown as follows.1. Continuous ohmic heating device of liquid food was designed and made, including power supply section and liquid road section. This device resolved some key problems such as the electrode pollution when works for long hours. Experimental device was designed. So the voltage, duty cycle, frequency of the device can be adjusted smoothly. The acquisition of the voltage and current, which are high frequency and non-sinusoidal, was realized. So the device is able to research the soy milk changes in the characteristics under different electric field conditions. Pressure of heat chamber and velocity can be adjusted, so heat time can be controlled and boiling will be prevented。2. Test device is designed to real-time acquisition of larger frequency range duty cycle bipolar square wave voltage and current signals. 3. Plate pollution in ohmic heating of soybean milk was researched. The reason for pollution is adhere to soybean milk protein. Resistance of adhesion properties is larger than that of soybean milk, so the heating speed is higher, and then the speed of pollution is increased. The most effective way to solve the pollution is to increase the power frequency. Study found that pollution can be effectively reduced when the power frequency is higher than1000Hz. Change of solids content will not change the influence of frequency over pollution.4. Within ohmic heating process, the thermal denaturation of the soy protein and soy milk in the air exposure time will increase the conductivity of the milk.5. The proteins in the adhesion of the electrode plate will occur fouling, and soybean milk conductivity measurement value will decrese.6. Change of soybean milk conductivity was researched in soybean milk ohmic heating. Time of exposure in the air can affect the soybean milk conductivity. Although the conductivity of soybean milk will change at different frequency, variation with temperature is liner. Soybean milk solid content can affect conductivity but the variation law will not be changed.Critical issues of ohmic heating technology and further research are summarized. Theoretical and experimental basis are provided for ohmic heating technology’s popularization and application. |
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