Permittivity of Mixtures of Saponaria vaccaria and Ethanol–Water Solution for RF Heating Assisted Extraction of Saponins

Abstract

Saponins are used for the treatments of cancers and various infections. The use of radio frequency heating in extracting them from the mixture of particulate Saponaria vaccaria and ethanol-water solution has potentials in pharmaceutical and neutraceutical industries. This technique requires a thorough understanding of the dielectric properties of the mixtures. The dielectric properties of the mixtures were measured over the frequency ranging from 5 to 30 MHz using a computer-controlled precision LCR meter and a liquid test fixture. The effects of temperature, particle moisture content (MC), frequency, and ethanol concentration (EC) on the dielectric properties of the mixture and penetration depths were investigated at 13.56 and 27.12 MHz. The dielectric constants of the mixtures linearly increased with the particle MC and were more sensitive to it at higher EC of the solution. The dielectric loss factors increased with the particle moisture in somewhat quadratic fashion at 100% EC and linearly at 70%, 40%, and 10% ECs. The dielectric constant and the loss factor linearly increased with the temperature. The increments were more prominent at higher MCs and lower EC. The dielectric spectra of the mixtures monotonically decreased with increasing frequency. The dielectric constants and the dielectric loss factors dropped up to 33% and approximately 50%, respectively, when the frequency was increased from 5 to 10 MHz and then slowly decreased afterward. The penetration depths of the electromagnetic energy within the mixtures decreased with increasing frequency and ranged from 0.06 to 8.83 m at 27.12 MHz. Empirical, semiempirical, and theoretical models for the mixture dielectric properties were tested.