Limitations of Supercritical (CO2) Extraction

CO2 extraction vs traditional extraction.

CONs of CO2 extraction:

• Liquid CO2 behaves as a non-polar solvent, so extraction of polar compounds cannot be done properly; only non-polar and slightly polar organic compounds of low molecular weight are soluble in supercritical fluid
• Poorly extracted compounds include hydrocarbons, alcohols, aldehydes, acetones, esters, terpenes, carboxylic acids, some amino groups
• Substances that CO2 doesn’t extract at all (insoluble to supercritical) include sugars, proteins, polyphenols, tannins, waxes, inorganic salts, chlorophyll, carotenoids, citric acid, malic acid, high molecular weight compounds

• Cost is high and affects practicality due to the expense

References:

Essentials of Botanical Extraction: Principles and Applications By Subhash C. Mandal, Vivekananda Mandal, Anup Kumar Das

Flavours, their Encapsulation and Release. INSTITUTO SUPERIOR TÉCNICO TECHNICAL UNIVERSITY OF LISBON, PORTUGAL

Essential Oil Quality and Grades

Essential oils are by definition produced in one of two ways:

• Steam distillation (most herbs)
• Cold pressing (citrus and a few herbs)

These two methods produce a single grade of oil called an essential oil. If produced by solvent extraction, a different term is used, such as absolute oil or extract.

Different brands of essential oils made from the same species of plant made appropriately by either of the two methods listed above are by definition the same grade. Of course, like any botanical, the sensory qualities but not the basic chemistry of a species can change a bit depending on where it's grown, just as olives and grapes do, without affecting quality or grade.

There are three basic analytical tests to determine quality and identity of essential oils:

• Sensory testing performed by trained testers
• Infrared spectrum analysis (IR) that produces a chemical fingerprint of the oil
• Gas chromatography (GC) that produces a separation and quantification of individual chemical components in the oil

These techniques are used with all samples having to match strict specifications, official standards and reference samples to pass quality control before they can be sold by manufacturers following strict quality procedures. Reputable reference works used by oil chemists, such as the Guenther series, guide the testing.

If the original plant is edible then the essential oil is by definition food grade. Some examples are the citrus oils, peppermint, oregano, etc. If the plant is not edible then the oil is also not considered food grade; as with cedarwood, pennyroyal, or ylang ylang. Due to the small bottle size and the need for cautions, there is not typically a food label on these oils.

Much caution needs to be taken with these oils, as they are extremely concentrated and most can burn the skin and mouth if not diluted adequately, even if food grade. Don't swig them or apply undiluted to the skin if you don't know how to use the specific type of oil in question.