Mixture Design as a Tool for Optimization of Antimicrobial Activity of Selected Essential Oils

The study aimed to use a statistical method of mixture design to optimize the antimicrobial activity of Tea Tree (<i>Melaleuca alternifolia</i>), Rosewood (<i>Aniba rosaeodora</i>), and Lavender (<i>Lavandula hybrida</i>) essential oils against <i>Escherichia coli</i> PCM 2057, <i>Listeria monocytogenes</i> PCM 2191, and <i>Rhodotorula mucilaginosa</i> EPSC001. The antimicrobial activity of used essential oils and their mixtures were evaluated by the disc diffusion method. Moreover, the antioxidant activity of tested essential oils was determined by the DPPH• and CUPRAC methods, and total phenolic content was measured using the Folin–Ciocalteu method. Tea tree essential oil was characterized by the highest total phenolic content (0.59 ± 0.05 mg GAE/g) followed by lavender oil (0.27 ± 0.05 mg GAE/g), and rosewood oil (0.11 ± 0.02 mg GAE/g). The first two oils also had similar antioxidant activity. Furthermore, essential oil from the tea tree exhibited the highest antimicrobial activity against tested microorganisms, and based on the mixture design approach, the aforementioned volatile oil participated in optimized mixtures in the greatest amount.