Dielectric properties of grapes and sugar solutions at 2.45 GHz

Dielectric properties of grapes at 2.45 GHz were measured at moisture contents varying from 80 to 15% (wet basis) at temperatures ranging from 25-80 degrees C using the Open Ended Coaxial Transmission Line Technique. Both dielectric constant and loss factor decreased with decreasing moisture content. In low moisture samples these properties were found to be considerably influenced by higher temperatures. Dielectric properties of sugar solutions of varying concentrations (20-250% by weight in water) were also determined at different temperatures, and these values were compared to those of grapes of corresponding moisture concentration. Predictive models of the dieletric properties as functions of moisture content and temperature were generated using response surface methodology. The results are useful in estimating the volumetric heating of grapes by microwave energy, and these methods can be extended to sugar-based foods in general.