Comparison of the oxidative stability of linseed (Linum usitatissimum L.) oil by pressure differential scanning calorimetry and Rancimat measurements

摘要

The aim of this study was to compare the oxidative stability of linseed oil using the pressure differential scanning calorimetry (PDSC) and Rancimat methods, and to determine the kinetic parameters of linseed oil oxidation. Five cold pressed linseed oils were oxidized at different temperatures under PDSC (90–140 °C) and Rancimat (70–140 °C) test conditions. The oxidative stability of the linseed oils was calculated based on induction times (PDSCτmax, Rancimat τon), the Arrhenius equation and activated complex theory, frequency factors (Z), the reaction rate coefficient (k) for all temperatures, activation energies (Ea), Q 10 numbers, activation enthalpies (∆H ⁺⁺), and activation entropies (∆S ⁺⁺). The PDSC method was more convenient for the determination of the induction time of linseed oils than the Rancimat method. During oxidation measurement by Rancimat method, the linseed oil polymerized, which affected the measurements. The reaction rate coefficient increased with rising temperature during measurement by both methods. The activation energy values of linseed oil oxidation using the PDSC and Rancimat methods ranged from 93.14 to 94.53 and 74.03 to 77.76 kJ mol⁻¹, respectively. The Q 10, ∆H ⁺⁺, and ∆S ⁺⁺ values for the analyzed linseed oils were between 2.11–2.13, 90.54–91.30 kJ mol⁻¹, −33.20 to −30.90 J mol K⁻¹ calculated by PDSC measurements, and 2.23–2.32, 71.03–74.76, −59.42 to −49.08 J mol K⁻¹ by Rancimat measurements, respectively.