MEASURING FREQUENCY- AND TEMPERATURE-DEPENDENT PERMITTIVITIES OF FOOD MATERIALS

Authors: Nelson, Stuart; BARTLEY JR, PHILIP - OLD DOMINION UNIV, VA

Submitted to: IEEE Transactions on Instrumentation and Measurement
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2002
Publication Date: 12/1/2002
Citation: NELSON, S.O., BARTLEY JR, P.G. MEASURING FREQUENCY- AND TEMPERATURE-DEPENDENT PERMITTIVITIES OF FOOD MATERIALS. IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT. 2002. V. 51(4). P. 589-592.

Interpretive Summary: The electrical properties of materials known as dielectric properties, or permittivity, determine how materials interact with electromagnetic fields. For materials such as foods, these dielectric properties determine how rapidly foods will heat in a microwave oven. Knowledge about the dielectric properties of food materials is important in designing such products as dinners for preparation in microwave ovens and in considering other processes involving radio-frequency or microwave dielectric heating of food for preparation or for sterilization. These properties, which determine the behavior of the materials in dielectric heating processes, vary with the frequency of the applied electric fields and also with the temperature of the food materials. A technique was devised for measuring the dielectric properties of food materials at different frequencies and at different temperatures. It was then used to measure the dielectric properties of three different types of foods, a macaroni and cheese dinner preparation, ground whole wheat flour, and apple juice. The new data are presented, illustrating the diverse nature of the dielectric properties of foods and showing how they change with the frequency of the electric field applied and as the temperature of the foods change between freezing and boiling temperatures. The new data are important to engineers and scientists working on microwave food processing. They provide information useful in modeling the behavior of foods in these processes and in improving the processes and the quality of food products for the consumer.

Technical Abstract: 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.