Effect of extraction methods on kinetic, chemical composition and antibacterial activities of Tunisian Thymus vulgaris. L. essential oil

ABSTRACT

The present study aims to compare two innovative extraction techniques: microwave-assisted hydrodistillation (MAHD) and solvent-free microwave extraction (SFME) through traditional extraction techniques: hydrodistillation (HD) and steam distillation (SD) for their efficiency in the extraction of the volatile compounds from Tunisian Thymus vulgaris leaves; the kinetic, yield, composition and antibacterial activities of the essential oil were assessed in vitro. Results show that the essential oils extracted by microwaves were quantitatively (yield) similar to those obtained through the conventional methods, but qualitatively, essential oils analysed by gas chromatography–mass spectrometry (GC–MS) presented 17, 11, 11 and 8 compounds obtained through SFME, MAHD, SD and HD, respectively, mostly consisting of carvacrol (89.24–41.17%), followed by γ-terpinene (11.37–1.37%) and para-cymene (27.95–2.05%). The essential oils were screened for antibacterial activity against 5 microorganisms. All essential oils obtained by studied extraction methods showed the same resistance against Gram (−) and Gram (+) bacteria. The SFME method gave the best results: rapid kinetic of extraction (30 min vs. 35 min for MAHD, 120 min for SD, and 180 min for HD), less energy saving and cleanest process.

KEYWORDS:

• Antibacterial activity
• essential oil
• microwave-assisted hydrodistillation
• solvent-free microwave extraction
• Thymus vulgaris leaves

Acknowledgements

The authors are grateful to Dr Noomen Moussa from the National School of Engineering of Gabes, Tunisia (ENIG), for the GC–MS analysis. The authors are also grateful to the anonymous referees and the editor for helpful comments on an earlier draft.

Declaration of interest

The authors declare that there are no conflicts of interest.