Optimization of antioxidant combination of three Moroccan essential oils, and their effect in olive and argan oils under accelerated storage

This study examines the optimization of the antioxidant activity of Thymus serpyllum, Mentha pulegium, and Mentha piperita essential oils (EOs) and investigates the correlation between their chemical compositions and antioxidative properties, also the use of the optimal formula to preserve olive and argan oils— previously unexplored studies. Methodology: The major volatile constituents were determined by a GC-MS method, and antioxidant activities of the individual EOs, as well as their mixtures, were analyzed using a mixture design methodology. Furthermore, the efficacy of EO mixtures in mitigating oxidative deterioration in olive and argan oils during accelerated storage was evaluated. Among the tested EOs, T. serpyllum exhibited the highest antioxidant activity with an IC50 of 1.99 ± 0.85 µg/ml, followed by M. piperita with an IC50 equal to 2.86 ± 1.11 µg/ml. A ternary mixture composed of 39% T. serpyllum, 28% M. pulegium, and 33% M. piperita demonstrated enhanced antioxidant activity compared to the individual EOs (theoretical IC50 = 1.25 ± 0.07 µg/ml, and experimental one equal to 0.98 ± 0.27 µg/ml). Positive correlations were observed between antioxidant activity and key volatile constituents, including p-cymene, thymol, carvacrol, γ-terpinene, and linalool. Moreover, the optimized EO mixture effectively inhibited oxidative rancidity in olive and argan oils, exhibiting an efficacy comparable to that of butylated hydroxyanisole (BHA). The addition of the EO mixture to the olive oil delayed oxidation and we found only 7.50 ± 0.71 meq O2/kg on day 20. This value is close to that of olive oil with BHA, where the PI increased from 3.75 ± 0.35 meq O2/kg on day 1 to 6.00 ± 0.00 meq O2/kg on day 20. Argan oil with added EO mixture remained almost stable throughout the storage period and the PI only increased from 3.25 ± 0.35 to 4.00 ± 0.00 meq O2/kg. These findings underscore the potential of EOs, both individually and in combination, as natural antioxidants for food preservation. Their application may contribute to the development of more stable and health-conscious food products with enhanced consumer acceptability. However, further research is required to optimize their efficacy and address potential toxicity concerns.