Mathematical Models and Kinetic Parameters of the Oxidation of Leonotis nepetifolia Oil.

Abstract

The objective of this study was to evaluate the kinetic parameters of oxidation of Leonotis nepetifolia oil using mathematical models to determine its stability and shelf life. The oil was extracted by cold pressing and analyzed using the Rancimat method under a constant airflow of 15 L·h⁻¹ at temperatures of 100, 110, 120, 130, and 140 °C. Kinetic parameters were calculated by applying the Arrhenius equation and the activated complex theory. To estimate the oil’s shelf life, three mathematical models were used: logarithmic, exponential, and Malthusian, with model validation based on the coefficient of determination (R²). The results showed a decrease in the oxidative stability index with increasing temperature. The obtained values were Q10 = 2.22, activation energy (Ea) = 102.19 kJ·mol⁻¹, frequency factor (A) = 2.14·10¹² h⁻¹, enthalpy (ΔH) = 98.94 kJ, entropy (ΔS) = -19.53 J·K⁻¹, and Gibbs free energy (ΔG) = 106.59 kJ. The estimated shelf life was 6.22 years at 20 °C, 4.18 years at 25 °C, and 2.8 years at 30 °C. All three models showed excellent fit to the experimental data (R² = 0.999). These findings provide valuable insights into the oxidative stability and storage behavior of Leonotis nepetifolia oil, supporting its potential application in the food and cosmetic industries.