Another technology in the extraction space is super­critical fluid extraction (SFE) whereby a solvent is subjected to temperature and pressure conditions to adjust the properties to those intermediate to a gas and liquid in a dedicated reactor setup. This in turn effects the solubilization of solutes in a matrix (Wenclawiak, 1992). The main supercritical solvent employed is carbon dioxide. Carbon dioxide (critical conditions: T = 30.9 °C and P = 73.8 bar) is cheap, envi­ronmentally friendly and has generally recognized as safe status from the US Food and Drug Administra­tion. Supercritical CO2 (SC-CO2) is also attractive because of its high diffusivity combined with its easily tunable solvent strength (Herrero et al., 2010).

However, due to its chemical nature, it possesses several polarity limitations. As mentioned previously, solvent polarity is particularly important when extracting polar solutes and when strong matrix inter­actions are present. To augment the process, organic solvents are commonly added to the carbon dioxide extracting fluid to alleviate the polarity limitations (Handa, 2008). CO2 is gaseous at room temperature and pressure, which makes recovery very simple and provides solvent-free products, i. e. once the liquid depressurizes, the CO2 returns to a gaseous state, and only the extracted products remain. SFE using CO2 can be operated at low temperatures, which allows the extraction and integrity preservation of thermolabile compounds (Mendiola et al., 2007).