Dielectric properties of edible oils and fatty acids as a function of frequency, temperature, moisture and composition

Dielectric properties of 10 edible oils and 6 fatty acids were measured over the frequency range 100 Hz–1 MHz. The effects of temperature (20–45 °C), moisture content (0.02–0.31%), and fatty acid component on dielectric properties of oils were investigated. Results indicated that dielectric constant ε′ of the oils and fatty acids exhibited same frequency dependence, i.e., a general plateau from 100 Hz to 500 kHz and a decrease from 500 kHz to 1 MHz significantly (p < 0.05). The dielectric loss ε″ of the oils decreased with increasing frequency from 100 Hz to 13.2 kHz and then increased with increasing frequency. The ε′ of fatty acids increased with an increase in the number of double bonds or molecular chain length. The ε′ of oils were mainly affected by the C18 unsaturated fatty acids. Partial Least Squares (PLS) analysis provided reliable prediction of the main fatty acid components of oils. Both ε′ and ε′′ of oils decreased with increasing temperature. The ε′ of oil increased with increasing moisture content. The results obtained in this work could be useful for evaluating edible oil quality.