Dielectric Properties of Beans at Different Temperatures and Moisture Content in the Microwave Range

Abstract

Dielectric properties of common Mexican beans (Phaseolus vulgaris L.) were determined and analyzed at microwave frequencies (800-2500 MHz). The free-space transmission technique was employed for the measurements of three varieties ("Flor de mayo," "Bayo," and "Negro") with different moisture content (8.8-12.3%, w.b.) at 20, 30, 40, 50, and 60°C. The dielectric constant and loss factor of beans decreased with increasing frequency for a fixed temperature, and increased with increasing temperature at a fixed frequency. The dielectric constant increased with increasing moisture content, while the loss factor remained nearly constant. With these results, disinfestation or quality control measurements can be proposed for beans using microwaves.