Kinetic evaluation of non-isothermal crystallization of oxidized extra virgin olive oil

In this study, accelerated storage tests were carried out at 60 °C up to 20 weeks on three extra virgin olive oils (Evoos) with different total phenol contents and fatty acid compositions (named as EvooA, EvooB, and EvooC). Their oxidative statuses, evaluated by means of primary oxidation value and total phenolic content, were related to both the shapes of differential scanning calorimetry (DSC) cooling curves and thermal properties. DSC cooling curves were all deconvoluted as crystallization occurs in a quite narrow range, and the single steps are not well separated. The first deconvoluted DSC peak for the three samples tested, which occurs in the temperature interval between -45 °C and -30 °C, can probably be ascribable to the crystallization of tri-unsaturated triacylglycerols. A nonisothermal crystallization kinetic procedure, derived by the well-known isothermal Avrami equation, combined with the method of Ozawa, was applied to the first deconvoluted DSC peak only by processing the data related to this DSC peak. Results of the modified Avrami method were found in agreement with those of the Ozawa method. In particular, Avrami and Ozawa's exponents lie from 2 to 4 (being those of fresh samples always lower than those subjected to the accelerated oxidation test). Crystallization is relatively slow for fresh samples whereas after the first 4 weeks; it occurs faster in EvooB and EvooC. © Akadémiai Kiadó, Budapest, Hungary 2011.