Study of the biological activity of essential oils-water mixtures

Abstract

This study aimed to investigate the biological activity of aqueous mixtures of two essential oils. The mixtures were prepared by mixing certain amounts of lavender and clove oils with distilled water at room temperature. In the case of lavender oil, a relatively clear saturated aqueous phase was obtained after mixing with an excess of the essential oil. The clove oil formed stable oil-in-water emulsions. The antibacterial activity of the samples was tested against two model bacterial strains. The growth of the Gram-negative Escherichia coli K12 and the Gram-positive Bacillus subtilis 3562 was determined in 96-well microplates. A more prominent inhibition activity against E. coli K12 strain compared to B. subtilis 3562 for both oil-water mixtures was observed. A disk diffusion test indicated growth inhibition by the lavender oil during the tests against the Gram-positive strain (zones of around 11.7 mm) while clove oil inhibited both bacteria (12 mm - B. subtilis 3562 and 13.66 mm - E. coli K12). The DPPH free radical method showed no antioxidant activity for the aqueous solution of lavender oil. The pure lavender oil exhibited negligible activity compared to the gallic acid reference solution, the clove essential oil, and its emulsion. A quantitative relationship between the content of cloves essential oil in the emulsion and its radical scavenging capacity was demonstrated.