Skip to main content
ARS Home » Research » Publications at this Location » Publication #120930
Title: FREQUENCY AND TEMPERATURE DEPENDENCE OF THE PERMITTIVITIES OF FOOD MATERIALS

Author
item Nelson, Stuart
item BARTLEY, JR., PHILIP - OLD DOMINION UNIVERSITY

Submitted to: Electromagnetic Wave Interaction with Water and Moist Substances Proceeding
Publication Type: Proceedings
Publication Acceptance Date: 3/15/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: The electrical characteristics of materials, known as dielectric properties or permittivities, determine the way the materials interact with electromagnetic fields. In microwave heating or cooking of food materials, these dielectric properties, are important because they determine how rapidly foods will heat. The dielectric properties vary with temperature, so information about the changes in these properties as foods heat up is also important. The dielectric properties of foods also vary with the frequency of the electromagnetic fields that are applied to foods. There are several different frequencies allocated for radio-frequency (RF) and microwave power applications, which include microwave cooking of foods and RF and microwave processing of materials. The choice of frequencies for such applications may therefore depend on the dielectric properties of the food or other materials to be processed. Specialized equipment is needed for measuring the dielectric properties of materials, especially, when variation with frequency and temperature are to be determined. A method for measuring the dielectric properties of food materials is described in this paper, and the dielectric properties of some different types of food measured over a range of frequencies and temperatures are presented. Food materials included a macaroni and cheese dinner, whey protein gel, ground whole wheat flour, and apple juice. Information on the dielectric properties of these food materials and their variation with frequency and with temperature will be useful to those working on applications of RF or microwave energy for cooking, sterilizing, or other processing of such foods. Improved and safer food products for the consumer will likely result from research and development of such new processes.

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, whey protein gel, 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.