Application of Cold Atmospheric Microplasma Pretreatment to Enhance Essential Oil Recovery from Laurel (Laurus nobilis L.) Leaves: Comparative Study of Extraction Methods

Comparative studies of essential oil recovery from cold atmospheric microplasma (CAmP)-pretreated laurel (Laurus nobilis L.) leaves were performed using hydrodistillation, steam distillation, hexane extraction and subcritical CO2 extraction. CAmP-pretreated and untreated laurel leaves were analyzed in terms of microstructural changes, extraction kinetics and the chemical composition of the recovered essential oil. CAmP pretreatment intensified laurel essential oil recovery through the formation of additional microchannels (>200 μm) in the leaf tissue. The pretreated capillary-porous structure reduced the diffusion barrier and increased the oil recovery rate in CAmP-pretreated samples. The extraction rate of CAmP-pretreated laurel leaves was 19–27.2% higher, while the total extraction time was reduced by up to 50% compared with the untreated control samples to obtain equal oil yield volume. CAmP pretreatment also affected the main chemical characteristics of laurel essential oil. The total quantative composition of the identified target-component fraction in oils from untreated samples decreased in the following order: subcritical CO2 extraction (90.5%) > hexane extraction (88.2%) > steam distillation (77.4%). A similar order was observed after CAmP pretreatment: subcritical CO2 extraction (95.8%) > hydrocarbon-solvent extraction (89.9%) > steam distillation (84.5%). These results indicate that CAMP can be used as a pretreatment step to increase the essential oil recovery rate and improve essential oil quality.