Oxidation kinetics of speck fat: Insights into its oxidizability and antioxidant efficiency of Salvia officinalis L. and Origanum vulgare L. ethanolic extracts

This study aimed to determine the oxidizability of speck fat and the efficiency of natural antioxidants extracted from sage (Salvia officinalis L.) and oregano (Origanum vulgare L.) in inhibiting its oxidation using isothermal calorimetry. The rate of radical initiation (R_i) was controlled using azobis(isobutyronitrile) (AIBN) (R_i = 4.0 ± 0.1 × 10⁻⁹ M/s) to accurately determine the kinetic parameters. Propagation rate constant (k_p) and oxidizability index (O.I.) for speck fat were found to be 6.88 ± 0.08 × 10⁻³ M^-1/2 s^-1/2 and 21.77 ± 0.20 M⁻¹ s⁻¹, respectively. In terms of antioxidant efficiency (A.E.), oregano extract exhibited (P < 0.05) greater value compared to sage extract. When compared to synthetic antioxidants, oregano extract did not report significant different A.E. values. Furthermore, the rate constant of inhibition (k_inh) for both the extracts was in the order of 10³ M⁻¹ s⁻¹. These findings highlight the potential of isothermal calorimetry to determine kinetic parameters from oxidation measurements for solid fats and the role of natural extracts in food preservation.