Kinetic-thermodynamic study of the oxidative stability of Arbequina olive oils flavored with lemon verbena essential oil

Arbequina extra-virgin olive oils were flavored with lemon verbena (Aloysia citrodora) essential oil (0.1-0.4%, w/w), being evaluated quality parameters (free acidity, peroxide value, UV-extinction coefficients), oxidative stability, antioxidant and total reducing capacity. The kinetic-thermodynamic nature of the lipid oxidation was evaluated by Rancimat (110-150 degrees C). The essential oil addition promoted the antioxidant and total reducing capacities but, unfortunately, increased primary and secondary related quality parameters. Moreover, flavoring decreased the oils' oxidative stability. The kinetic-thermodynamic data showed that unflavored oils had significantly lower oxidation reaction rates (0.055-0.06492 h(-1)), more negative temperature coefficient (-0.0268 degrees C-1), higher temperature acceleration factor (1.852), greater activation energy (82.7 kJ mol(-1)) and frequency factor (10.9 x 10(9) h(-1)), higher positive enthalpy of activation (79.4 kJmol(-1)), lower negative entropy of activation (-131.8 J mol(-1)K(-1)) and greater positive Gibbs free energy of activation (129.95-135.23 kJ mol(-1)), showing that oils' oxidation was negatively influenced by the essential oil incorporation. Overall, oxidation had a non-spontaneous, endothermic and endergonic nature. Finally, olive oils could be satisfactorily classified (principal component and linear discriminant analysis) according to the flavoring level, using quality-antioxidant-stability or kinetic-thermodynamic datasets. The latter showed a less predictive performance, although ensuring the full discrimination of unflavored from flavored oils.

Automated summary

The addition of lemon verbena essential oil to Arbequina extra-virgin olive oils improved antioxidant and total reducing capacities but also increased primary and secondary quality parameters. However, the essential oil incorporation negatively influenced the oxidation of oils, decreasing their oxidative stability. The study also showed that unflavored oils had significantly lower oxidation reaction rates and different thermodynamic properties compared to flavored oils.