Essential oil
2007 Schools Wikipedia Selection. Related subjects: General Biology
| Plant oils | |
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| Types | |
| Vegetable fats | (list) |
| Essential oil | (list) |
| Macerated | ( list) |
| Uses | |
| Drying oil - Oil paint | |
| Cooking oil | |
| Fuel - Biodiesel | |
| Aromatherapy | |
| Components | |
| Saturated fat | |
| Monounsaturated fat | |
| Polyunsaturated fat | |
| Trans fat | |
An essential oil is a concentrated, hydrophobic liquid containing volatile aromatic compounds from plants. It is produced by distillation. Other extraction processes to obtain aromatic plant compounds include expression, or solvent extraction. Essential oils are used in perfumery, aromatherapy, cosmetics, incense, for flavoring food and drink, and to a lesser extent, in medicine and household cleaning products. They are valuable commodities to the fragrance and flavorant industries.
Essential oil is also known as volatile oil and ethereal oil. It may also be referred to as "oil of" the raw plant material from which it was extracted, such as oil of clove. The term essential is intended to indicate that the oil is the fragrant essence of the plant from which it is extracted and not in the more common sense of being indispensable. It is not to be confused with essential fatty acids.
Medical use of vegetable oils has a long and distinguished history. Many oils that are use medicinally are essential oils, which are distilled rather than pressed or otherwise extracted. Medical properties claimed by those who sell medicinal oils vary from skin treatments to remedies for cancer, and are often based on historical use of these oils for these purposes. Such claims are now subject to regulation in most countries, and have grown correspondingly more vague, to stay within these regulations.
Interest in such uses of essential oils has enjoyed a revival in recent decades, with the popularity of aromatherapy, in which oils are heated and volatilized.
Production
Distillation
Today, most common essential oils, such as lavender, peppermint, and eucalyptus, are distilled. Raw plant material, consisting of the flowers, leaves, wood, bark, roots, seeds, or peel, is put into an alembic (distillation apparatus) over water, As the water is heated the steam passes through the plant material, vaporizing the volatile compounds. The vapors flow through a coil where they condense back to liquid, which is then collected in the receiving vessel.
Most oils are distilled in a single process. One exception is Ylang-ylang ( Cananga odorata), which takes 22 hours to complete through a Fractional distillation.
The water recondensed from the distillation process is referred to as a hydrosol, hydrolat, herbal distillate or plant water essence, which may be sold as another fragrant product. Popular hydrosols are rose water, lavender water, lemon balm, clary sage and orange blossom water. The use of herbal distillates in cosmetics is increasing. Some plant hydrosols have unpleasant smells and are therefore not sold.
Expression
Most citrus peel oils are usually expressed mechanically, or cold-pressed. Due to the large quantities of oil in citrus peel and the relatively low cost to grow and harvest the raw materials, citrus-fruit oils are cheaper than most other essential oils. Lemon or sweet orange oils that are obtained as by-products of the commercial citrus industry are even cheaper.
Prior to the discovery of distillation, essential oils (EO) were extracted by pressing.
Solvent extraction
Most flowers contain very little volatile oil to undergo expression and their chemical components are too delicate and easily denatured by the high heat used in steam distillation. Instead, a solvent such as hexane or supercritical carbon dioxide is used to extract the oils. Extracts from hexane and other hydrophobic solvent are called concretes, which is mixture of essential oil, waxes, resins, and other lipophilic (oil soluble) plant material.
Although highly fragrant, concretes contain large quantities of non-fragrant waxes and resins. As such another solvent, often ethyl alcohol, which only dissolves the fragrant low-molecular weight compounds is used to extract the fragrant oil from the concrete. The alcohol is removed by a second distillation, leaving behind the absolute.
In supercritical fluid extraction, supercritical carbon dioxide is used as a solvent. This method has many benefits, including avoiding petrochemical residues in the product. It does not obtain an absolute directly. The supercritical carbon dioxide will extract both the waxes and the essential oils that make up the concrete. Subsequent processing with liquid carbon dioxide, achieved in the same extractor by merely lowering the extraction temperature, will separate the waxes from the essential oils. This lower temperature process prevents the decomposition and denaturing of compounds and provides for a superior product. When the extraction is complete, the pressure is reduced to ambient and the carbon dioxide reverts back to a gas, leaving no residue. Although supercritical carbon dioxide is also used for making decaffeinated coffee, the actual process is different.
Production quantities
Estimates of total production of essential oils are difficult to obtain. One estimate, compiled from data in 1989. 1990 and 1994 from various sources gives the following total production, in tonnes, of essential oils for which more than 1,000 tonnes were produced.
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Oil Tonnes Sweet orange 12,000 Mentha arvensis 4,800 Peppermint 3,200 Cedarwood 2,600 Lemon 2,300 Eucalyptus globulus 2,070 Litsea cubeba 2,000 Clove (leaf) 2,000 Spearmint 1,300
Essential oil use in aromatherapy
Aromatherapy is a form of herbal medicine, in which healing effects are ascribed to the aromatic compounds in essential oils and other plant extracts. Many common essential oils have medicinal properties that have been applied in folk medicine since ancient times and are still widely used today. For example, many essential oils have antiseptic properties, though some are stronger than others. In addition, many have an uplifting effect on the mind, though different essential oils have different properties.
Solvents
Essential oils are usually lipophilic compounds. It thus has been found that alcohols, such as methanol and ethanol (primarily 100% concentrations), or organic solvents, such as acetone, are the best diluents to be used for dilution. Water is not recommended as water and fats do not dissolve in one another, although oil dilution in water can be achieved at extremely low concentrations of oil, and depending on the viscosity of the oil.
Raw Materials
Essential oils are derived from various parts of plants. Some, like orange oil, are derived from any of several parts of the plant.
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Berries
- Allspice
- Juniper
Bark
- Cassia
- Cinnamon
- Camphor
- Cedar
- Rosewood
- Sandalwood
Rhizome
- Ginger
Leaves
- Basil
- Bay leaf
- Cinnamon
- Common sage
- Eucalyptus
- Lemon grass
- Melaleuca
- Oregano
- Patchouli
- Peppermint
- Pine
- Rosemary
- Spearmint
- Tea tree
- Thyme
- Wintergreen
Resin
- Frankincense
- Myrrh
Peel
- Bergamot
- Grapefruit
- Lemon
- Lime
- Orange
- Tangerine
Root
- Valerian
Rose oil
The most well-known essential oil is probably Rose oil, produced from Rosa damascena and Rosa centifolia. Steam-distilled rose oil is known as "rose otto" or "attar of roses" while oil which is solvent-extracted is known as "rose absolute".
Dangers
Because of their concentrated nature, EO's generally should not be applied directly to the skin in their undiluted or "neat" form. Some can cause severe irritation or provoke an allergic reaction. Instead, essential oil should be applied with a plants oils or other fats (carrier oil), such as olive, hazelnut, or any other "soft" oil. Common ratio of essential oil disbursed in a carrier oil is 0.5–3% (most less than 10%) and depends on its purpose. Some EO's including many of the citrus peel oils, are photosensitizers, increasing the skin's reaction to sunlight and making it more likely to burn.
Industrial users of essential oils should consult the material safety data sheets (MSDS) to determine the hazards and handling requirements of particular oils.
- Pesticide residues
There is some concern about pesticide residues in EO's, particularly those used therapeutically. For this reason, many practitioners of aromatherapy choose to buy organically produced oils.
- Ingestion
While some advocate the ingestion of essential oils for therapeutic purposes, this should never be done except under the supervision of a professional who is licensed to prescribe such treatment. Some very common EO's such as Eucalyptus are extremely toxic internally. Pharmacopoeia standards for medicinal oils should be heeded. EO's should always be kept out of the reach of children. Some oils can be toxic to some domestic animals, cats in particular. Owners must ensure that their pets do not come into contact with potentially harmful essential oils.
- Smoke
The smoke from burning essential oils may contain potential carcinogens, such as polycyclic aromatic hydrocarbons (PAHs). Essential oils are naturally high in volatile organic compounds (VOCs). The internal use of essential oils should be fully avoided during pregnancy without consulting with a licensed professional, as some can be abortifacients in dose 0.5–10 ml.
- Toxicology
LD50 of most EO or their main components are 0.5-10 g/kg (orally or skin test).