Efficiency of Ohmic assisted hydrodistillation for the extraction of essential oil from oregano (Origanum vulgare subsp. viride) spices

Abstract

Abstract The aim of this work was to investigate the effects of Ohmic heating-assisted hydrodistillation (OAHD), applied at different voltages (100, 150, and 200) V, on the qualitative and quantitative characteristics of extracted essential oil from oregano herb ( Origanum vulgare subsp. viride ), compared to a conventional hydrodistillation (HD) procedure. The compositions of the extracted essential oils (using OAHD and HD) were assessed using gas chromatography - mass spectrometry (GC–MS). A 2,2-diphenyl-1-picrylhydrazyl free radical (DPPH) method was applied in order to evaluate antioxidant activity. The antimicrobial activity as well as the minimum inhibitory concentration (MIC) values of the samples against Bacillus cereus, Escherichia coli O157:H7, Salmonella Typhimurium, Pseudomonas aeruginosa , and Staphylococcus aureus were determined. Among 50 identified compounds; thymol and 4-terpineol were the most abundant components independently of the technique used (OAHD or HD). No significant differences were observed between HD and OAHD (all voltages) methods in terms of extraction yields, and between HD and OAHD (at 100 V) in terms of antioxidant activity (the half inhibition concentration values (IC 50 ) were 33.4 μg/mL and 31.2 μg/mL, respectively). However, the extraction time was significantly reduced when OAHD extraction was used compared to HD. For the antimicrobial activity, the MIC values indicated higher inhibitory activities against S. aureus and B. cereus (with similar MIC values of 6.25 μg/mL) than P. aeruginosa (25 μg/mL). However, no significant influence was observed between the different applied voltages and the two extraction methods. OAHD could thus be used as “green” extraction method compared to HD. Industrial relevance The production of essential oils at industrial scale is mainly performed using conventional hydrodistillation method. However, the increasing need in applying more efficient and sustainable extraction processes has led researchers to evaluate new alternative non-conventional methods in order to replace the existing ones. Among non-conventional technologies applied to extract essential oils from plant materials, Ohmic-assisted hydrodistillation is of great potential. It allows reducing the extraction time compared to conventional hydrodistillation, which reduces significantly the energy consumption. The implementation of Ohmic-assisted hydrodistillation technology in essential oil producing industries is therefore of great importance.