Application of arrhenius kinetics to evaluate oxidative stability in vegetable oils by isothermal differential scanning calorimetry

Abstract

In this study, 10 different vegetable oils were oxidized at four different isothermal temperatures (383, 393, 403, and 413 K) in a differential scanning calorimeter (DSC). The protocol involved oxidizing vegetable oils in a DSC cell with oxygen flow. A rapid increase in evolved heat was observed with an exothermic heat flow appearing during initiation of the oxidation reaction. From this resulting exotherm, the onset of oxidation time (T o ) was determined graphically by the DSC instrument. In our experimental data, linear relationships were determined by extrapolation of the log (T o ) against isothermal temperature. The rates of lipid oxidation were highly correlated with temperature. In addition, based on the Arrhenius equation and activated complex theory, reaction rate constants (k), activation energies (E a ), activation enthalpies (∆H ‡ ), and activation entropies (∆S ‡ ) for oxidative stability of vegetable oils were calculated. The E a , ∆H ‡ , and ∆S ‡ for all vegetable oils ranged from 79 to −104 kJ mol −1 , from 76 to −101 kJ mol −1 , and from −99 to −20 J K −1 mol −1 , respectively. Based on the results obtained, differential scanning calorimetry appears to be a useful new instrumental method for kinetic analysis of lipid oxidation in vegetable oil.

Oxidative stability of camelina (Camelina sativa L.) oil using pressure differential scanning calorimetry and Rancimat method

“…s on values from Rancimat tests presented in Table 2 were higher from s max values obtained using the PDSC method for all temperatures tested. The reason for this may be the size of tested samples (3-4 mg for PDSC in comparison with 2.5 g for Rancimat tests), which is emphasized by Tan et al [18]. It could be also explained by the fact that oil in Rancimat tests is oxidized using air containing approx.…”

“…Several researchers [17,18,[30][31][32]35] compared results of oxidation stability obtained using DSC and traditional oxidative tests, such as Rancimat. However, no research concerning the application of PDSC technique and Rancimat test in the analysis of camelina oil oxidation kinetics was found.…”

“…The highest differences (s max ) are correlated with rapid increase in peroxides concentration (propagation of autooxidation). However, the Rancimat method evaluates later oxidation stage, the time (s on ) that elapses until secondary (volatile) reaction products appear [17,18].…”

“…3 and 4 are 99 % identical with results obtained during experiments. Due to such a high goodness of fit, using these charts, it is possible to determine induction times for temperatures, in which research was not conducted [16][17][18].…”

“…Metrohm Rancimat (Europe) test and OSI-oxidative stability index (USA)-are commonly applied for analysis of edible oils [16,17], however, they cannot always be successfully used to analyze cold-pressed oils, despite being useful in assessing refined oils. Studies on oil oxidation using the DSC technique, under both isothermal (constant operating temperature) and dynamic conditions (linear temperature growth), have been carried out so far [17][18][19][20]. Nevertheless, studies were mostly conducted on refined oils [17,20,21].…”