Comparative Study on the Essential Oils Extracted from Tunisian Rosemary and Myrtle: Chemical Profiles, Quality, and Antimicrobial Activities

Rosemary (Rosmarinus officinalis L.) and myrtle (Myrtus communis L.) are perennial herbs, typical of the Tunisian flora, with an intense aromatic flavor. Their essential oils, obtained by hydro-distillation, were analyzed by gas chromatography coupled to mass spectrometry and by infrared Fourier transform spectrometry. In addition, these oils were assessed for their physicochemical properties as well as their antioxidant and antibacterial activities. The physicochemical characterization proved to be of good quality by analyzing pH, water content (%), density at 15 degrees C (g/cm3), and iodine values according to standard test methods. The study of the chemical composition allowed for the identification of 1,8-cineole (30%) and alpha-pinene (40.4%) as the main constituents of myrtle essential oil, while 1,8-cineole (37%), camphor (12.5%), and alpha-pinene (11.6%) were identified as principal components in rosemary essential oil. The evaluation of their antioxidant activities permitted to obtain the IC50 values, which ranged between 22.3 and 44.7 mu g/mL for DPPH and between 15.52 and 28.59 mu g/mL for ferrous chelating assay, for rosemary and myrtle essential oils, respectively, thus indicating that rosemary essential oil is the most effective antioxidant. Furthermore, the antibacterial activity of the essential oils was tested in vitro against eight bacterial strains by the disc diffusion method. The essential oils showed antibacterial effects on both Gram-positive and Gramnegative bacteria.