This work aims to apply isothermal calorimetry for the determination of the oxidative stability of bulk oils by deriving kinetic and thermodynamic parameters. The method consists of measuring the heat flow produced during the oxidation of the oils in the presence of oxygen. To this purpose, an oil was recovered from olive seeds, the solid waste derived from the transformation of olives, by using two different technologies: supercritical carbon dioxide and mechanical press. The oxidative stability of both extracted oils was then compared with commercial sunflower, soybean, corn, and rice oils. The kinetic and thermodynamic parameters, obtained from the analysis of isothermal calorimetry traces at 60 °C, allowed the calculation of the oxidizability index obtaining the following ranking: olive seeds by supercritical carbon dioxide (3.55 ± 0.4 × 10−3 (s/M)0.5) > sunflower (3.42 ± 0.8 × 10−3 (s/M)0.5) > olive seeds by mechanical press (3.07 ± 0.3 × 10−3 (s/M)0.5) > soybean (2.44 ± 0.6 × 10−3 (s/M)0.5) > corn (1.11 ± 0.4 × 10−3 (s/M)0.5) > rice oils (0.98 ± 0.4 × 10−3 (s/M)0.5). The results were then supported with the analysis of total phenolic content, antioxidant activity, fatty acid profile, and peroxide values. Overall, the findings of the present study support the use of isothermal calorimetry as a direct and non-invasive technique for determining the oxidizability of bulk oils.
Keywords: extraction technologies; isothermal calorimetry; oxidizability index; vegetable oils.