Kinetics of commercial olive oil oxidation: Dynamic differential scanning calorimetry and Rancimat studies

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Abstract

Four samples of olive oil were oxidized under polythermal (dynamic) conditions in the cell of a normal-pressure differential scanning calorimeter (DSC) and in the Metrohm Rancimat apparatus. The DSC experiments were carried out in an oxygen flow atmosphere using different linearly programmed heating rates in the range of 4–20 °C/min. Through DSC exotherms, the extrapolated onset temperatures were determined and used for the assessment of the thermal-oxidative stabilities of the samples. Using the Ozawa-Flynn-Wall method and the Arrhenius equation, the activation energies (Ea), pre-exponential factors (Z) and reaction rate constants (k) for oil oxidation under DSC conditions were calculated. The Rancimat measurements of oxidation induction times were carried out under isothermal conditions in an air atmosphere at temperatures from 100 to 140 °C with intervals of 10 °C. Using the Arrhenius-type correlation between the inverse of the induction times and the absolute temperature of the measurements, Ea, Z, and k for oil oxidation under Rancimat conditions were calculated. The primary kinetic parameters derived from both methods were qualitatively consistent and they help to evaluate the oxidative stabilities of oils at increased temperatures.

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