Optimization of Microwave Assisted Hydrodistillationon Chemical Compositions of the Essential Oils from the Aerial Parts of Thymus pubescens and Comparison with Conventional Hydrodistllation

Microwave assisted hydrodistillation (MAHD) was applied for the extraction of the essential oil from the aerial parts (tops) of Thymus pubescens. The MAHD method has been compared with conventional hydrodistillation (HD) technique, in terms of extraction time, yields and chemical compositions of the essential oils. The obtained results show similar chemical profiles for both methods. The extracted essential oils involved 14 components constituting 94.1 % and 96.3 % of the chemical profiles for the HD and MAHD methods, respectively. In the water distilled oil, carvacrol (30.3 %), thymol (27.1 %), alpha-terpineol (19.9 %), beta-caryo-phyllene (3.3 %) and geraniol (2.2 %) constitute most of the composition while in the oil separated using the MAHD approach, carvacrol (32.2 %), thymol (29.3% ), alpha-terpineol (18.5 %), beta-caryophyllene (2.9 %), linalool (2.3 %) and geraniol (2.2 %) contribute as dominant compounds. Based on the respective profiles, in all of the oils, oxygenated monoterpenes such as alcoholic and phenolic ones contribute as dominant compounds. Also, the effect of microwave powers was investigated on extraction of some major constituents of T. pubescens essential oils. Our results confirm that main oxygenated monoterpenes such as carvacrol, thymol and alpha-terpineol require an optimum microwave power and time to enhance their isolated contents and to save energy.