The Research Of Detection Technology Of Water Activity In Foods Based On Peltier Effect

Foodborne disease is one of the problems of food security, which is an important factor inpublic health hazards. Having the spoiled food is the most common cause of foodbornediseases, and microbial contamination of food is the most important factor in deterioration offood. Microbial growth must rely on water. The water activity in foods is adopted to reflecthow much water of food can be used by microorganisms. The water activity is not only animportant index of food quality control, but also be the important parameter of food safetycontrol. Under certain conditions, to control the water activity in foods will embarrass thegrowth of microbes in food, and prevent the occurrence of deterioration of food.The national standard recommended methods are Conway dish diffusion and diffusion ofwater activity meter, which are used to determine the water activity in foods. The subject isfrom the focus of scientific and technological project of Henan Province (102102210124)"Intelligent Detector of water activity in agricultural products (foods)". By finding thecorrespondence among the dew point, equilibrium relative humidity and water activity, thesubject adopted detection principle of condensation dew point method to design the rapiddetection equipment of water activity in foods based on Peltier effect. The device chooses the32-bit new microcontroller as the core of detection system, and uses a Pt100to detect thetemperature. It adopted thermoelectric cooling as a cooling device and used smartintegration-improved digital PID to control the system. The device can achieve rapiddetection of water activity in foods and display the testing data.The main topics are as follows:(1)research the hardware circuit module of test-control system, including themicro-controller module, temperature measurement and control module, the condensationstate detection module and user interface module.(2)combined with temperature measurement principle of the bridge, study how toaccurately control the temperature of semiconductor cooling device, which is adopted toensure the measurement accuracy of dew point temperature to meet the detectionrequirements of water activity in foods.(3)discuss the application of how to use the optical detection in the measurement of thecondensation state, and do a lot of experiments to find the law of voltage value variation indetection circuit caused by the change of condensation.(4)according to the principle of the condensation dew point method, program the systemthat chooses LPC1114microcontroller as the core, including the micro-controllerinitialization procedures, human-machine interface program, temperature measurement andcontrol procedures, and integration-improved digital PID.The trial detection device, which was used to determine the water activity in foods, wasproduced. Experimental results showed that the device could determine the water activity infoods within5to10minutes, and the measurement and control of temperature could reach theaccuracy of0.1℃. The testing data of water activity were with the stability and goodrepeatability.