5.4.3.1. Advantages and disadvantages of extraction with supercritical CO₂

The advantages in using supercritical CO₂ are largely of a “health and safety” and environmental nature and relate to increased unease about the presence of organic solvent residues in material for human consumption. However it is also well established in certain applications that the extracts obtained are more acceptable to taste panels than extracts obtained in other ways. This in turn probably relates to the closeness to which the extracted flavour resembles that in the original plant.

• It can be easily recycled

• Chemically inert. (However Lorn (1988), notes the presence of some acetates on the raspberry extract, obtained with supercritical CO₂)

• Non flammable

• Has good solvent characteristics for non-polar and slightly polar solutes.

• It is a “natural” substance, present in mineral waters and part of the life cycle

• It is easily removed from the product

• The dissolving power and selectively can be controlled by selection of suitable pressure/temperature combination

• It has a convenient critical temperature (31.04ºC). This enables extractions to be carried out at comparatively low temperature (often as low as 40 or 50ºC), decreasing the risk of damage of thermalabile compounds.

• Most of the volatile components, which tend to be lost in hydrodistillation, are present in the supercritical extracts [Martinez de La Ossa et al. (1991) and Vardag and Korner (1995)]. Partly because of this, extracts obtained in this way tend to have flavour and taste, which are well liked by tasty panels.

• Extraction of natural raw material with supercritical CO₂, allows the obtaining of extracts which flavour and taste are perfectly respected and reproducible

• The supercritical fluid ability to vaporise non-volatile components (at moderate temperatures) reduces the r energy spent, when comparing to distillation.

• Once the pressure excess in the equipment prevents oxygen entry while extraction occurs, oxidation reactions don’t happen

• The number of solvents possible to be used on supercritical extraction is superior of classic organic solvents

• Supercritical fluids have a superior selectivity although they have an inferior solvent power than classic organic solvents

• Supercritical extraction can be connected directly to a chromatograph, allowing analysis immediately after extraction.

Many examples of the extraction of aromatic herbs with liquid and with supercritical carbon dioxide are giving by Moyler (1984, 1994), Naik et al. (1989) and Meyer-Warnod (1984). In addition, the table below lists literature references to the extraction of several herbs and spices using liquid or supercritical carbon dioxide.