Essential oil extraction: critical appraisal of conventional and novel techniques

Essential oils have been valued for centuries by communities worldwide. These aromatic and volatile compounds possess antioxidant, antibacterial and anti-inflammatory properties. These therapeutic properties are primarily attributed to the presence of monoterpenes and sesquiterpenes. Further, these oils are utilized as valuable ingredients in the industrial sector. Extraction from plant materials is a fundamental aspect of natural product research. There has been driving continuous efforts to develop more efficient and sustainable extraction techniques. Consequently, several green extraction methods, including supercritical fluid, microwave, ultrasound-assisted extraction, pressurized liquid, and pulsed electric field extraction, have been developed. This review describes and discusses the various extraction methods used to obtain essential oils from various plant matrices. These include conventional methods, such as solvent extraction, steam distillation, and hydrodistillation. This review provides comprehensive comparison of some conventional and novel techniques, highlighting their operating principles, applications, advantages, limitations, and their influence on the chemical composition of essential oils. This comparison offers valuable guidance for selecting the most appropriate selection technique based on the desired application and extraction objectives. Studies discussed in this review suggest that novel techniques used for oil extraction provide higher extraction yields, improved recovery of bioactive compounds, and reduced degradation of thermolabile constituents. Future research should focus integration of green extraction technologies with novel food applications. This review also summarizes recent advances in the essential oil extraction. Moreover, this review uniquely incorporates sustainability metrics, including energy consumption, solvent usage, and carbon footprint, to compare essential oil extraction techniques. It also highlights the role of biorefinery approaches and green solvents to improve process efficiency, reduce environmental impact, and support the development of sustainable industrial applications. Graphical Abstract