Dielectric Properties of Fish Flesh at Microwave Frequency

We investigated the dielectric properties of fish flesh samples, which are the most important parameter in microwave heating. Both raw and preheated samples were investigated since the microwave is used not only for heating, but also for reheating. The dielectric properties of three kinds of fish commonly consumed in Japan were measured from 10 degrees C to 90 degrees C, at 10 degrees C intervals. The influences of frequency, temperature, moisture content, lipid content, protein denaturation, and heat treatment on dielectric properties were examined. With increasing temperature, the dielectric constant of the raw samples decreased more sharply than that of the preheated samples, which was due to moisture loss during heating caused by protein denaturation. To investigate the influence of protein denaturation, Lichtenecker's formula was applied to estimate the dielectric properties of solid fish flesh. Results showed that the dielectric properties of fish flesh related to temperature were predictable by regression equations. Moisture content was the most important factor influencing the dielectric properties of the fish flesh samples during heating (reheating), while no significant effect was found to be directly caused by changes in the protein structure of fish flesh after denaturation.