Temperature dependence of refractive index and of electrical impedance of grape seed (Vitis vinifera, Vitis labrusca) oils extracted by Soxhlet and mechanical pressing


In this report, the temperature dependence of the refractive index and electric impedance of vegetable oil grape seeds extracted from Vitis vinifera (v. Cabernet) and Vitis labrusca (v. Bordo) are investigated by means of experimental techniques. The seeds were collected from wineries located in two cities in the south of Brazil. In both extraction methods, the seeds were dried at 40.0 °C and at 80.0 °C, respectively, before the oil extraction. From optical microscopy and refractometry results, one can see that the grape seed oil extracted by mechanical pressing shows a linear dependence between the refractive index and temperature and has no bire-fringent residues. From the fitting of the EIS (Electrical Impedance Spectroscopy) data, an equivalent electric circuit composed of a parallel RC in series with a resistor is proposed. The circuit model is in good agreement with the experimental data and provides the electrical permittivity of the vegetable oils investigated.