Kinetic and thermodynamic parameters of curcumin in edible oils with different degrees of unsaturation

Abstract

The antioxidant activity of curcumin (0.02-0.1%) was evaluated in olive, sesame, and safflower oils at 373, 383, and 393 K. The results were examined in contrast to the effects of tocopherol (0.1%) and BHT (0.02%), so that the inhibitory function of curcumin was evaluated comparatively. The activation energy of oxidation was determined for olive (82.94 kJ·mol-1), sesame (77.39 kJ·mol-1) and safflower oils (74.42 kJ·mol-1). Adding curcumin (0.1%) enhanced the activation energy by 26.26, 26.64, and 38.81% in the case of olive, safflower, and sesame oils, respectively. Based on Gibbs free energy, curcumin functioned more effectively in olive oil at 373 K (growth coefficient: 1.52%), compared to the action of the other two antioxidants, namely tocopherol (1.43%) and BHT (1.39%). The efficiency of curcumin was lower in oils which had a higher degree of polyunsaturation due to the disproportionation of the hydrogen-donating mechanism and the rate of free-radical formation in these oils.