The Frequency and Temperature Dependence of Dielectric Food Data As Determined By A Cavity Perturbation Technique*

Abstract

Earlier reported dielectric measurements of ours for a number of moist foodstuffs at 2800 MHz in the temperature range —20°C to +60°C have been extended to the frequencies of 450 and 900 MHz, using the same kind of measuring technique, The results have, throughout, been reproducible and in good agreement with literature data, where available. Good agreement is also demonstrated between our data and those using a different measuring technique. Within the frequency range studied, ε_r’ tends to increase and ε_r” increases significantly with falling frequency for most foods. In all cases dielectric data rise sharply with temperature during thawing. With continued temperature rise, ε_r’ decreases gently, while ε_r” increases at the two lower frequencies for foods in general and at all three frequencies for salty materials. Penetration depth increases with falling frequency at low to moderate temperatures, hut the difference between frequencies diminishes rapidly with rising temperature. The combined influence of frequency and temperature is such, that calculated temperature profiles for microwave cooking of food slabs showed no important difference between the frequencies.