Measuring frequency- and temperature-dependent permittivities of food materials

An open-ended coaxial-line probe was used with sample temperature control equipment designed for use with the probe to measure permittivities of some liquid, semisolid, and pulverized food materials as a function of frequency and temperature. Graphical data for the dielectric constant and loss factor of homogenized macaroni and cheese, ground whole-wheat flour, and apple juice illustrate the diverse frequency- and temperature-dependent behavior of food materials and the need for measurements when reliable permittivity data are required.