Abstract
The application of microwave heating to food processing, including microwave oven, have come into wide use because of their ability to heat and cook food quickly and conveniently. However, a problem that has arisen in microwave heating is uneven heating or non-uniform temperature distribution in the foods. To control the uneven heating, it is important to know the mechanism of heating and the role of the dielectric properties of food, because they determine the heat generation when the food is irradiated by the microwaves. First of all in this manuscript, the principle of the microwave heating and the role of water in the microwave heating are explained. Next, the influence of the water and salt content on the dielectric properties of food was described. Reduction of water content primarily changes the dielectric constant, whereas the addition of salt primarily changes the dielectric loss factor. Finally, the physical properties change according to the thawing of food was described. The thermal and dielectric properties of food vary with temperature in thawing process, and the great difference in dielectric properties between frozen state and thawed one can cause a problem in uniform thawing, that is known as runaway heating.
