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Essential oil

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An essential oil is a concentrated, hydrophobic liquid containing volatile aromatic compounds extracted from plants. It may be produced by distillation, 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 . They are valuable commodities to the .

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.

Contents

Production

Prior to the discovery of distillation, essential oils (EO) were extracted by pressing, and this is still the case in cultures such as Egypt. Traditional Egyptian practice involves pressing the plant material, and then burying it in unglazed ceramic vessels in the desert for a period of months to drive out water, the water having a smaller molecular size diffuses through the ceramic vessels while the larger essential oils do not. The lotus oil in Tutankhamen's tomb, which retained its scent after 3000 years sealed in alabaster vessels, was pressed in this manner.

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 a holding vessel. The vessel is typically a florentine flask which has a spout at its bottom as well as in its middle. This flask allows essential oils which are lighter than water and float above it to be drained off using the middle spout, and allows heavier oils that sink below the water to be drained using the bottom spout.

Most oils are distilled in a single process. One exception is Ylang-ylang (Cananga odorata), which takes 22 hours to complete distillation. It is fractionally distilled, producing several grades (Ylang-Ylang "extra", I, II, III and "complete" in which the distillation is run from start to finish with no interruption).

The water recondensed from the distillation process is referred to as a hydrosol, hydrolat, or plant water essence, which may be sold as another fragrant product. Popular hydrosols are rose water, lavender water, and orange blossom water. Many 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.

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, since these solvents effect effectively remove all hydrophobic compounds in the raw material. The solvent is then removed by a lower temperature distillation process and reclaimed for re-use.

Although highly fragrant, concretes are too viscous and occasionally solid at room temperature due to high-molecular weight, non-fragrant waxes and resins that are present. 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. These types of essential oils, from plants such as jasmine and rose, are called absolutes.

In supercritical fluid extraction, high pressure carbon dioxide gas (up to 100 atm.) is used as a solvent. This method has many benefits. For one, it avoids petrochemical residues in the product. It also dissolves less of the non-fragrant waxes out of the raw material, thus allowing one to get the absolute directly without having to deal with a concrete. Finally, the lower temperature of the process and the chemical stability of the solvent prevents the fragrant compounds from decomposing or being denatured. This process is identical to one of the techniques for making decaffeinated coffee.

Production quantities

Main high-volume products - turpentine; orange and lemon (see orange oil), mint and citronella are essential oils. In ~2000, tonnes:

Rose oil

The most well-known essential oil is probably Rose oil (Rosa damascena, Rosa centifolia). Steam-distilled rose oil is know as rose 'otto' or 'attar of roses' while oil which is solvent-extracted is know as rose 'absolute'. Rose otto is usually dark olive-green in color and will form white crystals at normal room temperature which disappear when the oil is gently warmed. Rose absolute is a deep reddish brown with no crystals. It takes many pounds of rose petals to distill one ounce of essential oil. To mitigate the cost, some dishonest dealers will dilute rose oil with Geranium (Pelargonium graveolens) or Palmarosa (Cymbopogon martinii) EO's, both of which are rich in geraniol, the main constituent of rose oil. Some of these 'rose oils' are up to 90% geranium or palmarosa to 10% rose. This is referred to as extending the Rose fragrance. Sometimes rose oil is adulterated with other chemicals such as phenylethanol, which, although a natural component of rose oil, is usually artificially produced. This may be done to compensate for chemotype, e.g. Bulgarian distilled Rose oil is naturally low in phenylethanol, and Ukrainian or Russian Rose oil is naturally high in phenylethanol. Most Rose oil is produced in Bulgaria, Morocco and Turkey. Recently, China has begun producing Rose oil as well.

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.

Oils with standarized content of components (marked FCC, for Food Chemical Codex) have to contain X amount of certain aroma chemicals that normally occur in the oil. But there is no law that the chemicals cannot be added in synthetic form in order to meet the criteria established by the FCC for that oil. For instance, lemongrass essential oil has to contain 75% aldehyde to meet the FCC profile for that oil, but that aldehyde can come from a chemical refinery instead of from lemongrass. To say that FCC oils are "food grade" then makes them seem natural when in fact they are not necessarily so.

Undiluted essential oils suitable for aromatherapy are termed therapeutic grade, but in countries where the industry is not regulated, therapeutic grade is based on industry consensus and it not a regulatory category. Some unscrupulous providers take advantage of this situation to make misleading claims. Likewise, claims that an oil's purity is vetted by mass spectrometer or gas chromatography have limited value, since all such testing can do is show that various chemicals occur in the oil. Many of the chemicals that occur naturally in essential oils are manufactured by the perfume industry and are used to adulterate essential oils because they are cheaper. There is no way to distinguish between these synthetic additives and the naturally occurring chemicals. Consider that the most expensive oils are almost certainly adulterated.

The best instrument for determining whether an essential oil is adulterated is an educated nose. Many people can distinguish between natural and synthetic scents, but it takes experience.

Since essential oils are so potent, many can irritate the skin and can cause toxic reactions like liver damage and seizures unless diluted with a carrier oil. Fat plant oils (sweet almond oil, olive oil, hazelnut, rosehip seed, etc.) are examples of carrier oils.

Oils vary in price based on the amount of the harvest, the country of origin, the type of extraction used (steam distillation, CO2 extract, enfleurage), and how desirable the oil is. Indian Sandalwood is considered more desirable than Australian Sandalwood, based upon the aroma, and is twice as costly, mainly because the species that yields Indian Sandalwood essential oils is endangered. Organic and wild harvested essential oils also tend to be more expensive.

Popular uses

Solvents

Essential oils are usually lipophilic compounds so it 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, also 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.

Berries

Seeds

Bark

Wood

Rhizome

 Leaves

Resin

 Flowers

Peel

Dangers

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.

Toxical data: LD50 of most EO or their main components are 0.5-10 g/kg (orally or skin test).

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.

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.

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. [link]

References

Schnaubelt, Kurt. Advanced Aromatherapy: The Science of Essential Oil Therapy. Healing Arts Press, 1999. ISBN 0892817437

Sellar, Wanda. The Directory of Essential Oils Essex: The C.W.Daniel Company, Ltd. Reprint, 2001. ISBN 0 85207 346 1

Tisserand, Robert. Essential Oil Safety: A Guide for Health Care Professionals. Churchill Livingstone, 1995. ISBN 0443052603

See also

External links

 

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