Dielectric properties of potato puree in microwave frequency range as influenced by concentration and temperature

Abstract

Dielectric properties of potato flour-water dispersions (slurry) were measured in the frequency range of 500-2500 MHz by the open-ended coaxial probe method using a network analyzer as a function of concentration (10-25% w/w) and temperature (20-75oC). Both commercial and laboratory prepared samples of potato flours were used. Results indicated that the dielectric constant (') decreased with temperature and frequency while increased with concentration. The loss factor ('') increased with frequency and concentration; however, temperature showed mixed effect. Both ' and '' data in conventionally used microwave frequencies (915 and 2450 MHz) were studied as function of concentration and temperature for two sample types using a response surface methodology and found to follow 2nd order polynomial models. Temperature and concentration contributed significantly on dielectric spectra of potato slurry and the sample source had some effect. A change in ' and '' above 70oC could be attributed by starch gelatinization. Penetration depth (Dp) decreased with an increase in frequency and non-systematic with temperature. Addition of salt substantially reduced Dp of potato slurry.