91C-24 |
Dielectric properties of food relevant to RF and microwave pasteurization/sterilization |
Y. WANG1, T. D. Wig1, J. Tang1, and L. M. Hallberg2. (1) Department of Biological Systems Engineering, Washington State University, PO Box 646120, Pullman, WA 99164-6120, (2) Advanced Processing and Packaging Team, Combat Feeding Program, Soldier Systems Center, U.S. Army Soldier and Biological Chemical Command, Kansas St., Natick, MD 01760-5018 When a food product is retorted to achieve commercial sterility and shelf-stability, the severe degradation of color, flavor, texture, and nutrients is unavoidable. Dielectric heating has potential to replace conventional retort for many heat sensitive foods because of a rapid and uniform heating by direct interaction of RF or microwave energy with the polar components in the food to generate frictional heat. To properly design an effective dielectric heating system it is desirable to determine the factors that affect the rate of heating and uniformity of electric field intensity in foods. The dielectric properties of foods are the principal parameters that determine the coupling and distribution of electromagnetic energy during RF and microwave processing. Those properties are often temperature dependent, and therefore, must be known over the full range of temperatures experienced by the product to allow accurate prediction of heating behavior. The objective of this research was to study the dielectric constants, loss factors, and penetration depths of whey protein gel, liquid whey protein mixture, macaroni noodles, cheese sauce, and macaroni and cheese over a temperature range from 20 to 121.1 °C at frequencies of 27, 40, 915, and 1800 MHz. The open-ended dielectric probe method along with a custom-built temperature-controlled test cell was used in this study. It was found dielectric constants of all measured samples increased at 27 MHz and 40 MHz radio frequencies, and decreased at 915 MHz and 1800 MHz microwave frequencies as temperature increased, while dielectric loss factors increased with temperature at all 4 frequencies. The penetration depths at radio frequency range were about 4 times as much as that at microwave frequencies. The measured dielectric properties will be of great use in developing dielectric heating processes, and for developing appropriate new food receipts most suited for dielectric heating. They should also allow accurate simulation of a dielectric heating to expedite the development of new heating apparatus and processes.
Session 91C, Food Engineering: Food process engineering
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