FREQUENCY AND TEMPERATURE DEPENDENCE OF THE DIELECTRIC PROPERTIES OF FOOD MATERIALS

Authors: NELSON, STUART; BARTLEY JR, PHILIP - OLD DOMINION UNV, VA

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2002
Publication Date: 7/17/2002
Citation: NELSON, S.O., BARTLEY JR, P.G. FREQUENCY AND TEMPERATURE DEPENDENCE OF THE DIELECTRIC PROPERTIES OF FOOD MATERIALS. TRANSACTIONS OF THE AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS. 2002. 45(4). P. 1223-1227.

Interpretive Summary: The dielectric properties (electrical characteristics) of food materials are of interest not only because these properties determine the rate of heating in microwave ovens or in radio-frequency and microwave heating processes, but also because they can be used for rapid sensing of quality factors such as moisture content. Scientifically, the study of dielectric properties of materials and the behavior of these properties at different frequencies and different temperatures can be helpful in understanding the way in which water is bound to constituents in the foods and helps in understanding the nuances concerning the role of water in foods. A technique is described in the paper for measuring the dielectric properties of food materials over wide ranges of frequency of the applied electric fields and temperature of the food sample. Dielectric properties data are presented for such measurements of a macaroni and cheese dinner preparation, a whey protein gel, ground whole wheat, and apple juice. The resulting dielectric properties behavior, with respect to frequency and temperature, is compared for some of the food materials. An obvious conclusion is the need for measuring the dielectric properties of food materials when reliable data are needed, because the diverse behavior of the dielectric properties of different foods makes prediction of food behavior very difficult when it is exposed to radio-frequency and microwave heating. The new data will be helpful to food scientists working with microwave processing and to those preparing foods for the microwave food convenience market. The measurement technique described will also be useful to other scientists in the food microwave heating field.

Technical Abstract: An open-ended coaxial-line probe was used with network and impedance analyzers and a sample temperature control assembly, designed for use with the probe, to measure the dielectric properties of some food materials as a function of frequency and temperature. Graphical data for the dielectric constant and loss factor of a macaroni and cheese dinner preparation, whey protein gel, ground whole-wheat flour, and apple juice illustrate the diverse frequency- and temperature-dependent behavior of the dielectric properties of food materials.