Supercritical fluid extraction (SFE)
One of the alternative methods for extracting essential oils is
supercritical fluids. SFE is based on the use of solvents in their
supercritical state, meaning that they are exposed to temperatures and
pressures above their critical points. SCF have a unique property and
are between the liquid and gas phases, which depends on the pressure,
temperature and composition of the liquids [4, 6]. The most widely
used solvent for this extraction is carbon dioxide, CO2(figure 9). Because it has modest critical conditions
(Pc: 72.9 atm, and Tc: 31.2oC), unaggressive for heat sensitive compounds
[57], it has no any toxicity and is nonflammable, it is available in
high purity at low cost, it can be easily removed from the obtained
extract [58], No solvent remains in the final product [59] and
etc.
CO2 extracts show some of the properties of essential
oils and absolutes. Like essential oils, they have many beneficial
therapeutic properties and unlike absolutes, they are not extracted by
solvent and instead of chemical solvents, they are extracted using
CO2 gas under pressure and at room temperature.
In general, CO2 extracts has excellent quality and
better functional with biological activities [60] compared to
essential oil produced by hydro-distillation or liquid solvent [61,
62]. The high cost of capital and skills required in a supercritical
carbon dioxide extraction plant, as well as the wide range of
applications of this process, limit it except for large flavor
producers. rosemary, fennel and anise essential oils were obtained by
supercritical fluid extraction. The results showed that extraction of
supercritical fluids to obtain extracts is economically viable.
[63]. Supercritical CO2 extraction of essential oil
from lavender was performed by E. Reverchon [64]. This compound
showed 34.7% efficiency of the oil.