Extraction of Essential Oils from Plants by Hydrodistillation with Pulsed Electric Fields (PEF) Pre-Treatment

Essential oils, EOs, are concentrated liquids with complex mixtures of volatile organic compounds that can be extracted from different plant materials. EOs have been used by humans throughout history due to their natural properties: from pleasant fragrances, to anti-bacterial/fungal activities. This work presents the impact of pulsed electric fields, PEF, application as a pre-treatment for the extraction of EOs from eucalyptus, rosemary, and thyme leaves. The initial PEF pre-treatment was first applied to eucalyptus and rosemary leaves two weeks after harvesting, with a 2 kV/cm electric field and a specific energy of approximately 10 kJ/kg, followed by EO extraction by hydrodistillation, HD, with distillation times of 30 and 60 min. The best results were obtained for PEF pre-treated samples and 30 min HD, exhibiting an increasing trend in the average extraction yield of approximately 17% and 11% for eucalyptus and rosemary, respectively, in comparison with no PEF applied. The composition of the EOs extracted from eucalyptus was analyzed for their total phenolic content, TPC, where PEF pre-treated samples showed a higher polyphenol extraction, reaching 30% for 30 min HD. Finally, the optimization of the PEF pre-treatment was also studied, for maximizing the quantity of EO extracted from dry thyme leaves, while aiming for a minimization of energy consumption, for different distillation times. For this study it was observed that, for this plant material, an electric field of 1 kV/cm with 0.4 kJ/kg and an HD time of 30 min, after PEF application, was able to achieve an extraction yield up to 40% higher than the conventional method.