ABSTRACT
A substance is in a supercritical state when both its pressure and temperature are higher than its critical pressure and temperature. Supercritical fluids, due to their liquid-like density and gas-like viscosity, are very well suited for extraction of valuable substances from plant materials. The most frequently used supercritical solvent is supercritical carbon dioxide (SC-CO
) because of the following characteristic attributes:
Strong dependence of solvent properties on pressure and temperature, enabling wide control of solvent power in a broad range of operating conditions
Easy separation of extract from the solvent by depressurization provides a distinct separation of solute from solvent since CO
is gas at ambient conditions
High diffusivity of solutes in supercritical fluids and, consequently, high mass transfer rates
No traces of organic solvents in extracts Thermo-labile components are not exposed to high temperatures (critical
point temperature and pressure of CO
are 31.1C and 74 bars, respectively) No degradation of residual botanic material that can be used as foodstuff,
feedstuff, or as a source of substances insoluble in supercritical solvent
The main drawback of supercritical fluid extraction (SFE) is higher capital cost of the necessary high-pressure extraction equipment, compared to conventional extraction. Supercritical CO
is the solvent of choice in the SFE of bioactive components from plant materials. Since CO
is an environmentally friendly compound, it presents an alternative to hazardous traditional solvents. Though its solvent power for nonpolar compounds is lower than that of many organic solvents and it is even lower for the polar compounds (this disadvantage can be partially overcome by the addition of a polar modifier to the solvent), benefits of SC-CO
prevail. Besides the advantages mentioned above it is also inflammable, nonexplosive, cheap, and easily accessible. About 100 industrial plant materials using SC-CO
are onstream worldwide, most of them processing natural products for the food industry, nutraceuticals, or phytopharmaceuticals.
