Essential oils are found in the roots, stems, leaves and flower of a plant. After processing procedures, they form a clear liquid or a yellow to amber colour.
Essential oils are hydrophobic phytochemicals made up of volatile organic compounds. These volatile compounds or aromas give the plant its distinctive fragrance. Although essential oils are fat soluble, they do not contain the fatty acids that are usually found in oils.
How are they produced?
Essential oils are produced by extraction or expression. The most commonly used form of extraction is steam distillation, in which steam passes through the plant material, causing the ‘oil sacs’ in the plant to rupture. The steam carries the recently ruptured oil as a vapour, and when the vapour is cooled the essential oil and water separate, usually with the essential oil floating to the top.
Another method of extraction for essential oil is expression, which is done cold and is a more mechanical process. Expression involves the fruit or plants being loaded into a drum, with thousands of spikes on the inside. As the drum starts revolving the spikes rupture the ‘oil sacks’ and the essential oils run out the side.
The molecular structure of the essential oil is similar to the structure of natural oils. They are similar in that they are based on the linking of carbon and hydrogen atoms chains but the similarities end there.
Most of the essential oil structures are rarely in chains but are more ring structures with a diverse range of sub groups called ‘functional groups’. As the name suggests the ‘functional groups’ coming off the carbon chain structure provide the benefits or properties that are often found in the essential oils. There are eight aromatic molecules defined by their functional group:
- Monoterpene Alcohols: which are antibacterial and antifungal
- Sesquiterpene Alcohols: which provide the anti-inflammatory, anti-viral properties
- Aldehydes: which are known for being a disinfectant and anti-inflammatory
- Esters: are known to cause antispasmodic and anti-inflammatory properties
- Ethers: have been found to be antimicrobial and antispasmodic
- Ketones: have been found to have regenerative properties to the skin.
- Oxides: Provide a stimulant and expectorant effect
- Phenols: are strongly antimicrobial and are known stimulants to the immune and nervous system
Due to the chemical nature of essential oils and the volatile aromas they possess, essential oils are thus quite susceptible to heat and evaporation which is one of their main limitations. Due to the hydrocarbons in essential oils, they don’t tend to succumb to hydrolytic rancidity, but if essential oils are stored incorrectly they can oxidase and deteriorate.
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