Background: Combining various essential oils (EOs) for developing pharmaceutical formulations has been the focus of attention in recent years.
Objectives: This study aimed to determine the antioxidant effect of the combination of three Eos obtained from clove (Syzygium aromaticum L.), lemon peel (Citrus limon L.), and thyme (Thymus vulgaris L.) by using mixture design.
Methods: The EOs of lemon peel (EOL), clove (EOC), and thyme (EOT) as well as their combination were analyzed using a gas chromatograph with flame ionization detector (GC/FID). The antioxidant activities of the EOs from EOL, EOC, and EOT as well as their combination were measured adopting DPPH assay. The construction and statistical analysis of the experiment were designed using the NemrodW (LPRAI, version 2000) software.
Results: EOL, EOC, and EOT were found capable of neutralizing DPPH radical. EOC was distinguished by its strongest antiradical activity with IC50=15.02±0.02 µg/mL. EOT had an IC50=29.20±0.12 µg/mL while EOL had 188.69±0.95 µg/mL. The positive standard BHT was detected to be IC50=24±0.02 µg/ mL. The optimal, combinative mixture of essential oils may have been determined based on these isoresponse curves which allowed fixing the ideal combinations of ingredient in terms of quantity to obtain an EO mixture possessing appreciable and optimal antioxidant characteristics. The predicted antioxidant properties determined by the mixing plan model were retained and the experiments were carried out respecting the contents of proposed ingredients of 25.7% EOT, 32.3% EOL, and 41.9% EOC equivalent to 15.42 mg, 19.38 mg and 25.14 mg, respectively. This resulted in arriving at an essential oil mixture with an experimental IC50=11.023±0.145 µg/mL which was similar to those of the predicted antioxidant properties with an order of 10.907±0.212 µg/mL and a non-significant difference of P<0.05, based on which the validity of the proposed mixing plan model was determined. The combined EO was also found to be rich in eugenol (32.35±1.13%), thymol (25.49±0.03%), and limonene (21.30±0.02%).
Conclusion: Statistical planning and the development of utility profiles for mixtures of essential oils may have been used to predict the optimal composition as well as to determine their antioxidant profile.