Dynamics and Aggregate Structuring of Water Molecules in Edible Oil Analyzed by Dielectric Spectroscopy

Abstract

Dielectric measurements for 10wt % W/O emulsion samples prepared with various surfactant concentrations between 0 and 10wt % were carried out in the frequency range of 40Hz up to 20GHz at room temperature during 2 hours at 15-minute intervals. Three distinct relaxation processes such as an electrode polarization in the kHz region, an interfacial polarization originated from ion dynamics on the interface of water and oil in MHz region, and an orientation polarization of oil molecules in the 100MHz region were observed. The relaxation time and relaxation strength of the interfacial polarization increased with time. These time dependences of the relaxation time and strength become more moderate with increasing surfactant concentration. In addition, these time dependences also suggest increasing water-droplet size and reflect stability of the dispersion system. In this study, all measurements were carried out with a cell type electrode, in which the water content was considered to be larger at the bottom of electrode, and the ε∞ value can be an indicator of the water content. The 1% surfactant W/O emulsion samples did not show an increase in the water content, but the relaxation time for the interfacial polarization increased much. This is an evidence of increasing water-droplet size, because the relaxation time of interfacial polarization is considered to reflect spatial scale of interface of water droplets. These results indicate a change in the W/O emulsion structure with time by dielectric spectroscopy.