Studies On The Correlation Between The Quality And Dielectric Property Of Fired Food

As a kind of convenient processed foods, the fried food has become more and more favorite by consumers because of its unique taste and flavor. However, there will be a series of complex physical and chemical changes during high-temperature frying. These changes not only declined the nutritional value of food, change flavor, but also produced some toxic substances which are harmful to health. During the food storage and transportation process, water content, water activity and equilibrium relative humidity are significant to the stability of food storage, which is the common index for the stability of food storage.Based on the dielectric properties and electrical conductivity measurement, this research explored the best conditions for LCR under low frequency. The changes of quality indicators for soybean oil and fried food were measured during frying in different times, and fitting with the changes of dielectric constant, relative dielectric loss and electrical conductivity, in order to find a new real fast detection technology.Found out the change rules of dielectric properties adapted to temperature and frequency in 100-100 000 Hz using the LCR impedance instrument. The results shown that the certain correlation have between electrical parameters with frequency and temperature of soybean oil. The best measuring condition were 100 000 Hz and 20 ℃.The changes of acid value, iodine value, carbonyl group value and polar component for soybean oil were measured during frying in four days, and fitting with the changes of dielectric constant, relative dielectric loss and electrical conductivity. The results shown that, by the increasing frying times, the acid value, carbonyl group value, polar component, relative dielectric constant and electrical conductivity for soybean oil were increased, instead of iodine value decreased. The relative dielectric constant, relative dielectric loss, conductivity and quality index of soybean oil during frying showed good correlation, especially the relative dielectric constant, the correlation coefficients were almost greater than 0.98.It is feasible to inspect the quality of soybean oil using dielectric parameters, and significant practical value to evaluate rapidly the quality of frying oil with dielectric properties.Then, the quality and electrical conductivity were studied in the frying time. By the increase of frying time, the moisture content of the grass fish fillets reduced, oil content, hardness and chewiness all showed a trend of rising, color showed deepened. The existence of diaphragm in the fish has a certain influence in conductivity measurement. By measuring can be learned that the muscle membrane connecting fiber has a major influence on electrical conductivity of two different types of muscles. The electrical conductivity and quality index of grass fish fillets during frying showed good correlation, the correlation coefficients were almost greater than 0.95, show that it is feasible to inspect the quality of grass fish fillets using electrical conductivity.The adsorption and desorption equilibrium moisture contents of grass fish fillets at varying temperatures(25, 35, 45 and 55 ℃) and a relative humidity in the range of 11-85% were determined by the static method to analyze the effects of temperature and relative humidity on both equilibrium moisture contents. Different equilibrium moisture content curves were fitted according to the five mathematical equations of Smith、Peleg、Oswin and Henderson. The study found that, the grass fish fillets of moisture absorption and desorption equilibrium moisture content were both decreased by the rise of temperature under the same condition of water activity. From a composition of fitting accuracy, it was found that the modified Smith model was the most suitable to describe the moisture absorption equilibrium moisture content of grass fish fillets, and the modified Oswin model was the most suitable to describe the desorption equilibrium moisture content of grass fish fillets...