Comparison of ohmic-assisted hydrodistillation with traditional hydrodistillation for the extraction of essential oils from Thymus vulgaris L.

Ohmic-assisted hydrodistillation (OAHD) is an advanced hydrodistillation (HD) technique utilizing ohmic heating process and could be considered as a novel method for the extraction of essential oils. One of the major problems with traditional methods is long extraction time. OAHD of essential oils from the aerial parts of Thymus vulgaris L. (common thyme) was studied and the results were compared with those of the conventional HD. The results showed that OAHD method had the extraction time of 24.75 min while this value was about 1 h for HD. Scanning electron micrographs of thyme leaves showed a sudden eruption of essential oil glands and their surrounding area for OAHD samples. GC-MS analysis did not indicate any noticeable changes in the compounds of the essential oils obtained by OAHD in comparison with HD. Results of this study introduced OAHD as a green technology because of less energy required per ml of essential oil extraction. Industrial relevance: The quality and quantity of essential oils extracted from herbs and other raw materials are affected by the extraction method. In this research ohmic-assisted hydrodistillation (OAHD) was used as an advanced and novel hydrodistillation (HD) technique and compared with traditional hydrodistillation in extraction of essential oils from the aerial parts of Thymus vulgaris L. (common thyme). OAHD method was quicker, more economical and environmentally friendly than hydrodistillation method. The results of this study introduced OAHD as a green technology.