Temperature Distribution in Foods

Microwave Heating of Foods Containing Starch (Part 2)

Abstract

Temperature distribution in spherical or cylindrical shaped foods or dielectrics heated in microwave oven was calculated on the condition that microwave was uniformly irradiated. When both the dielectric constant and the microwave power depth were large, temperature of the central portion of the sphere or the cylinder was observed to be higher than that of the circumference. Results of the calculation were demonstrated with fading patterns of iodine stained gelatinized starch in a beaker or in a cylindrical shaped vessel on microwave heating. The central portion dominantly faded regardless of the position of the vessel in the oven. On the other hand, when stained starch was put in a box on microwave heating, the central portion remained blue which conforms with the results of the calculation. Fading patterns of multimode of standing wave were observed in the case of thin depth of stained starch contained in a Petri dish or in a box. As an example of foods, water contents of inner and outer portions of mochi, a rice cake which was in a round shape on heating, were measured on microwave and conventional (electric heater radiation) heating. The water content of the inner portion of mochi decreased more rapidly than that of the outer portion on microwave heating, whereas the water content of the inner portion decreased only a little on conventional heating because of “case hardening” of mochi surface.