Moisture influence on the dielectric behavior of foods

Authors: Nelson, Stuart; Trabelsi, Samir

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 3/28/2008
Publication Date: 6/21/2009
Citation: Nelson, S.O., Trabelsi, S. 2009. Moisture influence on the dielectric behavior of foods. ASABE Annual International Meeting.

Interpretive Summary: The electrical characteristics of materials known as dielectric properties determine the way in which materials interact with radio-frequency (RF) and microwave electric fields. For example these dielectric properties determine how rapidly foods will heat in a microwave oven. Another example is the use of the dielectric properties of grain for rapidly sensing their moisture content, i.e., the amount of water in the grain. This is possible because the moisture content is highly correlated with the dielectric properties of the grain. Dielectric properties of food materials also vary with the frequency of the RF and microwave electric fields applied to the materials as well as with changes in moisture content and temperature of the materials. These changes in the dielectric properties with frequency and temperature can be referred to as the dielectric behavior of the materials. Understanding the dielectric behavior of food materials is important in applications such as microwave heating of foods and in using RF and microwave instruments for measuring moisture content and other quality characteristics of such materials. The dielectric properties of several food materials have been measured as they depend on frequency of the electric fields and the moisture content and temperature of those food materials. In this paper, the dielectric behavior of those food materials is examined as it is related to the moisture content, or amount of water in the foods. Thus, measurements on food materials with a wide range of moisture contents, including wheat grain, fresh chicken breast meat, several kinds of fruit, and apple juice were considered in the study. Results of dielectric properties measurements for the foods, ranging from 11% to 90% moisture content, are presented graphically and their dielectric behavior with respect to moisture content is discussed in detail. The findings are of interest to scientists and engineers in the food industry and those designing equipment for microwave heating and instruments for rapidly and nondestructively detecting food quality characteristics. Thus, results of the research will be helpful in improving efficiency for producers and processors and in improving food products for consumers.

Technical Abstract: The importance of dielectric properties of food materials is discussed with respect to their influence on the heating of materials by radio-frequency and microwave energy and their use for rapid, nondestructive sensing of quality characteristics of such materials. Data are presented graphically showing the frequency and temperature dependence of the dielectric constant and loss factor of wheat, fresh chicken breast meat, several fresh fruits, and apple juice, representing food materials with a wide range of moisture content. The influence of moisture or water content on the dielectric behavior of these materials is discussed, and that behavior is explained in terms of dipolar relaxation and ionic conduction.