Effect Of Ohmic Heating On The Activity Of Lipoxygenase In Soybean Milk And Simulation’s Study

Heat treatment of food is a very important step in food processing, it can not only improve the quality and taste of food, but also can play the role of sterilization. The heat treatment process involves energy consumption, food processing efficiency, operation complexity and many other aspects. So, finding a corresponding method is very important in the treatment of different food materials. Ohmic heating is a new heating technology in recent years, the basic principle is food materials as a part of the electric circuit, when the electric current passes through the food material, due to the inherent impedance characteristics of the food materials electricity directly within the food is converted into heat energy, so as to achieve the purpose of heating food. Ohmic heating has many advantages, such as fast heating speed, high energy conversion rate, uniform heating,precise control of heating quantity etc. The application of ohmic heating is very wide, it can heat the liquid food, at the same time can put fast and high temperature sterilization on solid and solid-liquid food. Ohmic heating technique research began relatively early in abroad,and continuous ohmic heating apparatus are being used successfully in USA, UK, and Japan. At present, the study of continuous ohmic heating devices of our country is in laboratory exploration. Related to the ohmic heating technique for the study of food quality is not many. So, further research for the effect of ohmic heating technology on food quality is very meaningful.This thesis mainly contains two aspects: The first part is to study the effects of ohmic heating on the soymilk lipoxygenase activity using self-made ohmic heating setup. The second is to simulate the ohmic heating process of soymilk with finite element analysis software. The main results are as follows:(1) In order to determine the content of lipoxygenase, The standard curve of lipoxygenase was determined by using lipoxygenase standard. By calculation, the lipoxygenase concentration of the raw milk( holland beans 12, bean water proportion 1∶10)was 0.15 mg/mL, and the activity was 2885 U.(2) In order to study the effect of different electric field conditions on the lipoxygenase in soybean milk, the ohmic heating device was used to carry out the ohmic heating treatment of soybean milk. Test results show that: In the heat preservation stage, the passivation of the lipoxygenase conformed to the first order kinetic equation, and the activity decreased with the prolonging of the holding time, and the passivation rate of the lipoxygenase activity gradually become slow.(3) The frequency of the power had effects on the activity of lipoxygenase in soybean milk, the higher frequency accelerated the passivation of lipoxygenase. While the power frequency was higher than 500 Hz, the power frequency change effect on lipoxygenase activity was not significant.(4) For the study of effect of ohmic heating on lipoxygenase activity in Soybean Milk,We heated soybean milk with the electric heating device, and compared with the traditional heating methods. Ensure the heating process of two kinds of heating methods consistent in the test process, to eliminate the influence of thermal effect. The study found that when the heating end temperature is the same, lipoxygenase activity in ohmic heating conditions in soybean milk were lower than conventional heating conditions. It can be concluded that the electric field can promote the passivation of lipoxygenase in soybean milk. The reason is that electric field acted on Fe3+ which is in the lipoxygenase activity center, resulting in changes of Fe ion status, so that lipoxygenase activity decreased.(5) The heating process of the static and continuous ohmic heating equipment is analysed with computer simulation technology.