30D-1 |
The influence of temperature and frequency on dielectric properties of aqueous ionic and non-ionic solutions at radio frequencies, 1 - 30 MHz |
C. DEFELICE, Food Research Program, Agriculture and Agri-Food Canada, 93 Stone Road West, Guelph, ON NIG 5C9, Canada and P. Piyasena, Food Research Program, Food Research Program, Agriculture and Agri-Food Canada, 93 Stone Road West, Guelph, ON NIG 5C9, Canada. Radio Frequency (RF) heating is a promising technology for food applications. The important factors that influence RF heating are dielectric properties of food materials. However, data on dielectric properties in the RF range are limited. The two important parameters describe the dielectric properties of a material are the dielectric constant and the dielectric loss factor that are measured relative to vacuum and are defined as the relative dielectric constant and the relative dielectric loss factor respectively. The dielectric properties depend on the compositions of the food product with water and salt being the two primary components that have the most effect on the heating ability of the product. A study was undertaken to investigate the dielectric properties of solutions made up of different compositions of salt, sugar and malic acid (0.2, 0.4, 0.6, 0.8 and 1.0%) in water and 0.27% guar solution in the RF range of 1-30 MHz at 0 - 80°C. A precision LCR meter connected to a test cell, which was placed in a glycol-water bath, was used to measure these properties. The dielectric properties were found to be most affected by the salt with the relative dielectric constant values increasing with temperature (from 207 at 0°C to 4353 at 80°C at 27.2 MHz for 1% salt) and decreasing with frequency (from 203 at 5 MHz to 146 at 30 MHz at 80°C for 1% salt). The relative dielectric loss factor also increased with temperature from 656 at 0°C to 2714 at 80°C at 27.2 MHz for 1% salt and decreased with frequency from 12781 at 5 MHz to 8901 at 30 MHz at 80°C for 1% salt. Malic acid and sugar had a minor affect. Salt, malic acid and sugar in guar solution behaved comparable to those in water. Data obtained in this study could be used in developing models to predict temperature increases during RF heating of multi component liquid foods.
Session 30D, Food Engineering: Physical and chemical properties
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