Commercial essential oil extraction methods

The traditional method of essential oil analysis is to extract the plant material by steam distillation or with solvent and then fractionally distil the oil or extract and isolate individual components by chromatographic techniques for subsequent identification by spectroscopic methods. At each step the odour of the fractions and isolates is assessed and those with the desired characteristics are investigated further. To answer the enquiry about the key odour components of broom absolute, first a sample of the absolute that is of an acceptable odour quality is obtained. The absolute is the alcoholic extract of the concrete, which is itself the solvent extract of the flowers of Spartium junceum, Spanish broom, often referred to by its French name Genet. The odour of any natural extract can vary according to the geographical origin and quality of the plant material, the time of year it is harvested and the extraction method used. If no sample of adequate quality is commercially available then the fresh flowers would be obtained from the plant and the extraction carried out in the laboratory. 

Steam distillation is the main commercial extraction procedure for the production of essential oils from almost any type of plant material. Solvent extraction is also used commercially and yields a resinoid, concrete or absolute according to the solvents and techniques used (see Chapter 4). Both steam distillation and solvent extraction are used on a laboratory scale to produce oils and extracts for analysis. Other methods of extraction, such as supercritical fluid extraction (SFE), which uses supercritical CO2 as the extraction solvent, are now being developed and used on both commercial and laboratory scales. The extracts produced by SFE may contain different materials from the steam-distilled oil because of the solvating power of C02 and the lower extraction temperature, which reduces thermal degradation. The C02 extract may therefore have an odour closer to that of the original material and may contain different fragrant compounds. The choice of extraction procedure depends on the nature and amount of material available, and the qualities desired in the extract. Solvent extraction is better suited to small sample amounts or volatile materi-... 

Methods using some type of atmospheric or reduced pressure steam distillation have been historically the most commonly used, and essential oils were (11) and are still frequently isolated this way on a commercial scale. The SDE or Likens Nickerson extraction method (12,13) was an extension of the Essential Oil industry s technique of cohobation where Ae condensed steam is separated fiom the volatile oil using a simple trap and returned to the still in order to minimize loss of water soluble volatiles. SDE had actually been described earlier in practical organic chemistry textbooks (14,15). The Likens Nickerson head though was simpler and easier to construct and control than the earlier organic chemist s version. Other versions of the head have been designed and used (2). 

Steam and steam/water distillation are the predominant extraction methods used. Other methods include solvent extraction, cold pressing, infusion, effleurage and water distillation. Distillation is a method that involves the evaporation and subsequent condensation of liquids in order to produce, refine and concentrate essential oils. High quality oils are distilled once only, while some commercial oils are purified by double or triple distillation methods. 

Three species of Echinacea are in medicinal use Echinacea ( .) purpurea E. angustifolia and . pallida. Depending on the species, the part of the plant (roots, herb) and the method of extraction (hydrophilic, lipophilic), the commercially available preparations of Echinacea contain varying concentrations of flavonoids, essential oils, polysaccharides, derivates of caffeic acid, polyacetylenes, alkylamides and alkaloids. Apart from a very few exceptions these preparations are not standardized in their content of any of these substances. The evidence available so far indicates that it is not a single component but the mixture of various groups of substances which is responsible for the observed immunomodulatory effects [5]. 

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