Study On Detecting Dielectric Properties Of Food Material In Microwave Heating Process

Dielectric properties of food, in terms of dielectric constant and dielectric loss factor, represent the ability of absorption and conversion of electromagnetic within material. When the electric field strength, the size and the shape are in constant level, the dielectric properties are the key indexes impacting the food quality in microwave processing conditions. Therefore, the control of food microwave process based on the dielectric properties of material may promote the technical level of food processing industry and products quality. According to existing research results, the temperature, moisture content and frequency are the main factors affecting the dielectric properties of the food.Raspberry fruit was selected as the experimental material, a mathematical model of dielectric properties was developed as function of temperature and moisture content under2450MHz microwave frequency. The dielectric properties of the food material can be indirectly detected based on the temperature and moisture content in the microwave field, which provide an effective measurement for the analysis of dielectric parameters of raspberry puree under the food processing.STM32series micro-controller chip STM32F103RBT6of STMicroelectronics company was selected as the core controller of the system hardware and a optical fiber temperature measurement method was used to detect the temperature changes of the food material. Moisture prediction model was applied to calculate the moisture content with time under the microwave power and the pressure. It was applied C language to design the system software which included the main system program, A/D conversion, digital filtering, least squares method, calculation of the dielectric properties, the liquid crystal display and data storage subroutine.The detection system of the temperature and the dielectric parameters were verified which used dielectric properties of the detection system as the platform and raspberry fruit as the experimental material. The results showed that the system had stable measurement data of dielectric properties of raspberry puree which water ratio was84%and the heating-up period was120seconds in microwave power4.02kW, vacuum pressure60kPa microwave processing conditions. Compared with the maximum theoretical value of the dielectric properties, the dielectric constant and the dielectric loss factor of maximum measurement error of raspberry puree were2.58and1.77, respectively. Detection errors of the system were within the scope of the requirements and expected design goal was achieved.