Determination of the oxidative stability of vegetable oils by Differential Scanning Calorimetry and Rancimat measurements

Samples of vegetable oils were oxidized at isothermal conditions in the cell of a Pressure Differential Scanning Calorimeter (PDSC) and in the Methrom Rancimat apparatus: The PDSC and Rancimat experiments were carried out at a temperature in the range of 90-160 degreesC. From resulting PDSC exotherms their times to reach the peak maximum (tau(PDSC)) were determined and used for the assessment of the oxidative stability of the samples. Similarly the measured Rancimat induction times (tau(Rancimat)) were used. As PDSC and Rancimat results were obtained at different temperatures the equations for temperature extrapolations of the tau(PDSC) and tau(Rancimat) values have been proposed. Using the Arrhenius type correlation between induction times and temperature and activated complex theory the reaction rate constants, activation energies, activation enthalpies and activation entropies for oils oxidation have been calculated.