Protective effect of hydroxytyrosol and rosemary extract in a comparative study of the oxidative stability of Echium oil.

The oxidative stability of Echium oil has been studied by two accelerated oxidation methodologies namely Rancimat and differential scanning calorimetry at selected temperatures in the range 50-110 °C. Kinetic analyses have provided Arrhenius parameters, oxidative stability indexes (OSI), temperature coefficients (t), Q and OSI at 20 °C (OSI) for both methodologies focussing on secondary and tertiary oxidation products. Peroxide, p-anisidine and polar compounds values have been measured to characterize from primary to tertiary oxidation products. In general, susceptibility of this oil to oxidation has been found to be larger than for other vegetable oils, according to the OSI values estimated by Rancimat and differential scanning calorimetry. However, the values of t and Q are found to be similar to those described for vegetable oils. In addition, a study of the influence of two antioxidants, namely hydroxytyrosol and rosemary extract on the oxidative stability of Echium oil has been carried out using both methodologies. Protective effects over oxidation by up to a threefold increase of OSI values have been found for both antioxidants at the highest dose utilized.