Dielectric Properties of Foods at 3 GHz as Determined by a Cavity Perturbation Technique.

Abstract

A series of measurements of dielectric properties for food materials were made in the temperature range —20 to +60°C using the cavity perturbation technique described in the first paper of this series. Variables studied besides temperature were preparation technique, pretreatment and composition of the food materials. Results obtained were consistent, reproducible and in fair agreement with literature data available. For moist foods a very sharp rise in dielectric properties is seen during thawing, followed by a gradual decrease with further temperature increase, except for salted foods where a continued increase with temperature in loss factor was found. A clear positive correlation between water content and ε′_r was found but not for ε"_r. Dielectric properties decreased with increasing fat content, and loss factor increased with salt content. In general, freezing, short time frozen storage, thawing and rate of heating had little influence on the data determined, with the exception of thickened gravy without stabilizer. Penetration depths are presented as a function of ε′_r and ε"_r, and the practical significance of the data obtained are discussed.