Effect of sonication on the dielectric constant of water and water + ethanol in ginger extraction

Abstract

The dielectric constant of solvents and solutes play important role to the extraction efficiency of a process through the ability of solutes to dissolve in solvent. The dielectric constant of water can be manipulated by introducing some external interventions such as temperature, entrainer and sonication. A lot of studies have been done on the effect of high temperature in decreasing the dielectric constant of water to 27 at 250oC [1, 2] to act as organic solvent. In this study, we are focusing on the lower temperature (25 – 55 oC) with ethanol as entrainer and sonication to decrease the dielectric constant of water. There were four major bioactive compounds from ginger extraction which were 6-gingerol, 8-gingerol, 10-gingerol and 6-shogaol. Those bioactive compounds were non-polar with slightly polar [3]. Distilled water and ethanol (95%, AR, J. Kollin Chemicals) were used to prepare the solvent mixtures. The dielectric constant of solvent was measured using Alpha TDR-5000 (Zadow Electronics, Germany) and the dielectric constant of solvent and ginger extraction was measured using Agilent 85070B dielectric probe with Network Analyzer (USA). The dielectric constant of distilled water decreases from 70.81 at 25oC to 66.10 at 55oC with sonication (28kHz, 100% power). Ethanol was added as the entrainer to decrease the dielectric constant of the solvent. As the percentage of ethanol increase from 5% to 30%, the dielectric constant also decreases. At 55oC, the dielectric constant of 5% ethanol in water was 66.10 and decreases as the percentage of ethanol increases to 30% with the dielectric constant of 58.29. The same trends were also shown as the temperature increases. Next, the polarities of water and water+ethanol with the present of ginger for ultrasonic extraction were studied. The results show different trends compared to without ginger presents which are almost the same trend as reported by [4]. The interaction of ginger with the solvent mixtures changed the dielectric constant of the mixtures. The dielectric constant of solvent mixtures and ginger lower than without ginger, but increased as the temperature increased. This can be explained by the solvation phenomena and disrupts the interaction between molecules in increasing the solubility and extraction efficiency.