On the Effect of Copper on Characteristics of the Insulating Extra Virgin Olive Oil Under Thermal Aging

In this work, we study the thermal aging of a local extra virgin olive oil at 90°C up to 1200 h, in the presence and the absence of copper (Cu). Physical analyses of samples by FTIR and UV-Vis spectroscopy show that the thermal stress induced structural alteration of the oil, which is more pronounced in the presence of Cu. The relative permittivity as a function of heating time is a little higher in the presence of Cu. It shows a slight decrease, attributed to the elimination of some polar compounds during the thermal treatment, which are compensated by other polar products resulting from the aging process. The dielectric dissipation factor of samples in the presence of Cu slightly increases with the heating duration. This can be explained by an increased amount of charge carriers resulting from Cu contamination. The total acid number related to both types of samples, as another fingerprint of the structural alteration, is found to be responsive to the heat treatment, exhibiting a dramatic increase in the presence of Cu. This behavior is attributed to the oxidation and hydrolysis processes in promoting acidic products, which is further favored and catalyzed by Cu. We also observed that the kinematic viscosity of samples at 40°C increases as the heating duration increases. This fact is attributed to the increase of the molecular weight as a result of the polymerization process, which is disadvantaged in the presence of Cu.