Differential scanning calorimetry thermal properties and oxidative stability indices of microwave heated extra virgin olive oils

DSC employment for the assessment of the deterioration effect of microwave heating on vegetable oils, and on olive oils in particular, has been partially explored in literature. The aim of this work was to evaluate the potentiality of DSC to discriminate among microwaved extra virgin olive oils (EvOo from different olive cultivar and origin), according to changes on thermal properties (upon cooling and heating) and traditional oxidative stability indices (peroxide, p-anisidine and TOTOX values). An elevated value of lipid oxidation was reached by the most unsaturated EvOo sample (9.5 % of linoleic acid) at 6 min of microwave treatment. Free acidity significantly increased (0.42 %) only for the oil sample with the highest water content (874 mg kgoil-1) at the longest time of treatment. Crystallization enthalpies significantly decreased and the major exothermic peak shifted towards lower temperature, leading to enlargement of the transition range in all samples due to the formation of weak and mixed crystals among triacylglycerols and lipid degradation products. On the contrary, thermal properties upon heating appeared to similarly vary among samples. The analysis of DSC thermal properties upon cooling seemed to clearly discriminate among different EvOo samples after microwaving. The relation between changes of thermal properties and oxidation parameters should be further studied using additional oxidative stability indices on a larger set of oil samples, due to the complexity of EvOo composition.