Dielectric Properties and Dipole Moment of Edible Oils Subjected to ‘Frying’ Thermal Treatment

• Published in: Foods Vol. 9; no. 7; p. 900
• Main Authors: Šegatin, Nataša, Pajk Žontar, Tanja, Poklar Ulrih, Nataša
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01-07-2020; MDPI
• Subjects: Absorption; Absorptivity; Accuracy; Dependence; Dielectric constant; Dielectric loss; Dielectric properties; Dielectric relaxation; dipole moment; Dipole moments; Edible fats and oils; Edible oils; Electric properties; Electrical conductivity; Electrical properties; Electrical resistivity; Evaluation; Fatty acids; Food science; Frequency ranges; Frying; Heat treatment; Lipids; Methods; Oils & fats; Onsager relationship; Oxidation; Parameters; Permittivity; Polarization; Refraction; Refractivity; Relaxation time; Vegetable oils; United Kingdom; United States > US; Japan; Germany
• DOI: 10.3390/foods9070900
• EISSN: 2304-8158

The dielectric properties of six refined edible oils with different fatty-acid compositions were determined for oils incubated at 180 °C up to 40 h. The oil degradation was evaluated by the dielectric dispersion and dielectric loss in the frequency range from 40 Hz to 2 MHz at 25 °C, refractive index, density, saponification number, and specific absorption coefficient at 232 and 268 nm. The dependence of the dielectric properties on frequency has been evaluated with Corach, Cole–Cole, and the universal power law models, giving the novel strategies for the interpretation of the dielectric spectra of thermally treated oils. The derived parameters—the dielectric constant, the electrical conductivity, the relaxation time τ and the exponents α, p, and n—are discussed with respect to the increased oxidation evidenced by specific absorption coefficients and polar products, as measured by the dielectric constant of the thermally treated oils. The specific refraction, specific polarization, orientation polarization, and dipole moment were determined using Lorenz–Lorentz, Debye and Onsager relationship. All above parameters obtained increased during the thermal treatment, except specific refraction, the electrical conductivity and the relaxation time. The dielectric constant-macroscopic parameter was compared with microscopic parameter polarization and dipole moment; the linear dependence was found to be R 2 = 0.971 .