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CHAPTER 7

ESSENTIAL OILS

DEFINITION

Essential oils are the concentrated aromatic oils of plant leaves, flowers, seeds, bark, roots and the rinds of some fruits. They evaporate on contact with air and are also known as volatile oils. They vary in strength but are always very potent and generally smell best when diluted. Essential oils obtained from trees are generally produced by a lengthy steam distillation process applied either to the resin, the chopped wood or the foliage and branch ends.

Essential oils have great many uses and may be obtained from either wild or cultivated plants. An estimated 3 000 essential oils are known of which approximately 300 are of commercial importance. The majority are obtained from agricultural plants but a number of oils are collected from wild sources including trees (Iqbal 1993). One commercial source of essential and fragrance oils lists over 50 different oils; 25 of which are used in cooking and over 20 are used in potpourri, crafting, cosmetics, massage, aromatherapy and other uses. Still other essential oils are used to repel insects and other arthropods that are pests of humans, livestock and pets (mosquitoes, fleas, ticks, etc.) (Thomas and Schumann 1992).
 

COMMERCIAL EXTRACTION METHODS

Removal of essential oils from plant material is accomplished by various methods, depending on the quality of the oil present and the stability of the aromatic constituents. The tendency of some constituents to undergo changes when subjected to high temperatures makes it necessary in some cases to use special methods of extraction to obtain the desired product without decomposition or alteration.

Four major methods of extraction are generally used:

In hydro distillation the plant material is in direct contact with water while in steam distillation, live steam is used. In water and steam distillation, both water and steam are used but the plant material is not in direct contact with water. In solvent extraction, the plant material is extracted with a solvent and then the oil is separated from the solvent. Each of these extraction methods can be carried out at reduced pressure, atmospheric pressure or excess pressure.

Before distillation, the plant material is often field cured, partially dried or disintegrated to some extent. This latter disintegration process, commonly referred to as comminution or size reduction, is used in the extraction or distillation of herbs or for their incorporation into food products. The reduction in particle size exposes as many oil glands as possible to the solvent or steam. It reduces the thickness of the plant material through which diffusion must occur, greatly increasing the rate of spread of vaporization and distillation of the essential oils (Thomas and Schumann 1992).
 

"CEDAR" OILS

Several members of the family Cupressaceae, which are important sources of essential oils, are commonly known as "cedars." These include members of the genera Cupressus, Juniperus and Thuja. The members of the genus Cedrus (family Pinaceae) are also known as "cedars" or "true cedars." Since the essential oils extracted from this group of trees are used for similar purposes, they will be discussed collectively in the following section.
 

Cedar leaf oil

Cedar leaf oil has been an item of commerce for over 100 years and is produced from the ends of branches and adherent foliage of the northern white cedar or arborvitae, Thuja occidentalis, and the western red cedar, Thuja plicata. According to one producer, this oil contains approximately 60 percent thujone a -thujone, b -thujone and fenchone). Cedar leaf oil is a common ingredient in pine and cedar blends that are used in room sprays, talcs and insecticides. This oil is also a component of embalming fluids, microscope slide slips, industrial cleaners, deodorants, pharmaceuticals, cleaning fluids, salves, liniments, perfumes, shoe polishes and soaps. One of the principal uses of cedar leaf oil is in the preparation of patent medicines such as cold-remedy salves, which help clear the nose and chest. Another use of this oil is to "re-odorize" sawdust which is in sawdust logs or instant fire logs.

The primary areas of production of cedar leaf oil have been north-eastern United States (New York, Vermont and, to a lesser degree, the Upper Peninsula of Michigan) and adjoining portions of Canada (eastern Quebec and south-eastern Ontario). Cedar leaf oil is also produced in British Colombia, Canada. Production of this oil has been a small industry controlled by local farmers who distil the oil in fairly crude equipment during times when they are not doing other farm work. In 1978, cedar leaf oil was selling at about US$21.00/kg. In 1984, an estimated 25 tonnes were produced in Canada and the United States (Thomas and Schumann 1992). One company, based in Quebec, Canada (Huiles Essentielles Branchex Ltd) produces about 4 500 kg of cedar leaf oil annually which it wholesales in 45 gallon drums. In January 1998, Cedar leaf oil retail price was US$7,87 for 1/3 oz. (see also at http://www.gritman.com/p169.htm for retail prices of this and other essential oils).

Essential oils from Juniperus and Cupressus

A number of essential oils are derived from the foliage, fruits and wood of various species of Juniperus and Cupressus world-wide. The oils distilled from the heartwood of Juniperus are used in the production of the majority of perfumes and colognes on the world market. More than 400 fragrances, or almost 60 percent of the fragrances produced, contain cedarwood oil (Anderson 1995). Several are important commodities in the international market.

Species
In the United States, essential oils are presently harvested from two species of Juniperus: the eastern red cedar, J. virginiana, of the eastern states and the Ashe juniper, J. ashei, a tree found in portions of Arkansas, Missouri, Oklahoma and Texas. The latter species is often referred to as J. mexicana; however, according to Little (1979), this taxonomic designation is not valid.

The oil harvested from J. virginiana is known in the essential oils trade as Virginian cedarwood oil or Cedarwood oil Virginiana and is recovered through the process of partial pressure steam distillation of sawdust, wood shavings, old stumps and chipped logs, materials which would otherwise be considered waste. Waste products from cedar furniture manufacturing plants are a prime source of material for extraction of this oil. Most production today comes from the state of North Carolina, United States, although at least one processor in Texas (Texarome Inc) also manufactures this oil. Virginia cedarwood oil is widely used in the fragrance industry in soaps, air fresheners, floor polishes, and sanitation supplies. It is also used in deodorants, insecticides (see textbox), mothproof bags, and janitorial supplies. In addition, a large percentage of this oil is used as a starting material for cedrol and cedryl acetate (Thomas and Schumann 1982).

The oil harvested from J. ashei is known as Texas cedarwood oil. This oil has different uses and does not compete with the Virginia cedarwood oil. The chemical composition of the two oils is similar, but Texas cedarwood oil is used almost exclusively as feedstock for the manufacture of chemical derivatives whereas Virginia cedarwood oil is used primarily in fragrance formulas. Unlike the Virginia cedarwood oil, the Texas cedarwood oil is not a by-product of the furniture industry. This tree is felled by ranchers to clear land for grazing. Cedar trees and stumps from these land-clearing operations are sold to distillation plants. Approximately 70 to 80 percent of this oil is used for cedrol isolation and subsequent acetylation (Thomas and Schumann 1982).

In China, Chinese cedarwood oil is extracted primarily from Cupressus funebris, a small tree or shrub that is found in Guizhou, Gansu and Sichuan Provinces. Other species used for production of this oil include Juniperus chinensis, J. formosana and J. vulgaris (Coppen 1995). This oil competes with the Virginian and Texas cedarwood oils and generally sells for a lower price. Price data given by Thomas and Schumann (1982) indicate that the price for Texas cedarwood oil was about US$6.05/kg while the lower grade Chinese oil was being offered in New York at US$3.74/kg. Mid-1997 spot prices (New York) for the three oils were US$4.60/kg (Chinese), US$15.20/kg (Virginian) and US$8.60/kg (Texas).

Commercial juniper berry oil is produced from the berries of Juniperus communis by steam distillation of the crushed, dried or partially dried berries. The spent berries from gin production (see Chapter 8) are generally used for this purpose. Juniper berry essential oil contains mainly the terpenes pinene, myrcene, sabinene and limonene. This oil is a watery white or very pale yellow, mobile oil, having a fresh, yet warm, rich balsamic woody sweet and pine needle like odour and is used in aftershave fragrances and other perfumery products (Good Scents Company 1996).

Oil of Savin is obtained by distilling the fresh leaves and shoots of J. sabiniana, a Mediterranean species. This oil is a powerful diuretic and has been used as an abortifacient (Hora 1981).

Destructive distillation of the wood of J. oxycedrus, another species indigenous to Mediterranean Europe and the Near East yields Oil of Cade or Juniper tar oil. Rectified Cade oil is a clear orange- brown to dark-brown oily liquid with an intense tar like, smoky phenolic odour. Its use in perfumery is limited to situations where a smoky, leathery, woody phenolic, dry and warm note is required (e.g. scented notepaper, leather products, pine for menís fragrances, etc.). Cade oil has certain disinfectant properties that allow it to be used in soap perfumes. Cade oil is also occasionally used to impart a smoky flavour to meat and seafood (Good Scents Company 1997). This oil has been used for treatment of skin diseases, especially psoriasis but is now largely replaced by coal tar derivatives (Hora 1981).
 


CEDARWOOD OIL - A NATURAL PESTICIDE?

Cedarwood oil is under investigation as a natural pesticide or repellent. The wood of several species of Juniperus, especially J. virginiana, is known to be decay resistant. Fences made from cedarwood posts are still sound after several decades of use. Cedar chests are known to be safe places to store woollen articles and protect them from the ravages of cloth moth larvae. Extracts from the wood of Juniperus recurva in Nepal have also been shown to have insecticidal properties (Adams 1993). Recent laboratory studies by USDA Forest Service indicate that cedarwood oil and perhaps cedar leaf oil may be effective termiticides when absorbed into other woods (Adams et al.1988). Numerous herbal and pet shampoos and natural repellents contain cedarwood oil as an active ingredient (Anderson 1995).

An essential oil is extracted from the heartwood of Juniperus macrocarpa, on a limited scale, in Yugoslavia where it is an ingredient of soap perfumes, detergents and disinfectants (Good Scents Company 1997). At one time, cedarwood oil was extracted from the wood of Juniperus procera, a tree indigenous to Kenya and other eastern African countries. This is no longer done because commercial timber harvesting of natural forests of this tree has been suspended in Kenya where the most extensive forests of this tree are found.

In addition to Juniperus ashei and J. virginiana, other North American species of Juniperus are potential future sources of cedarwood oils. Adams (1987) investigated cedarwood oil yields from 11 North American species of Juniperus with widespread distributions and significant biomass by steam distillation. He found that cedarwood oil yields from two species, J. erythrocarpa and J. scopulorumcompared favourably with those of J. ashei and J. virginiana. J. erythrocarpa is a multi-stemmed tree that occurs from west Texas to New Mexico and Arizona. J. scopulorum is a common tree of the Rocky Mountain region and is closely related to J. virginiana. He concluded that neither species would be competitive with the primary North American cedarwood oil producing species but could possibly support small, local distillation facilities.

Production standards
International (ISO) standards exist for both the Texas and Virginia cedarwood oils. For the former, the alcohol content, expressed as cedrol and in the range of 35-48 percent, is specified with a minimum cedrol content of 20 percent. For the Virginia cedarwood oil, a maximum cedrol content of 14 percent is stipulated. In the United States, recent FMA standards have replaced older EOA standards and are available for Chinese, Texas and Virginia cedarwood oils. These standards specify that for the Texas and Virginia oils the alcohols content (cedrol and related isomers) must range between 25-42 percent for the Texas oil and between 18-38 percent for the Virginia oil. The Chinese oil must have a minimum alcohol content of 8 percent (Coppen 1995).

Production and international trade
World-wide production statistics for the major essential oils of Cedrus (see following section), Cupressus and Juniperus are reported by Lawrence (1985) for the year 1984 (Table 7.1) and indicate a total production of about 2 117 tonnes.

Three of the oils discussed in this section: Chinese cedarwood oil, Texas cedarwood oil and Virginiana cedarwood oil are traded internationally in substantial volumes. According to Coppen (1995), Western Europe, Japan and the United States are the major markets for these oils. The United States utilizes much of its Texas and Virginia cedarwood oils and also imports a significant quantity of Chinese cedarwood oil (320-400 tonnes/year). Japan imports about 170 tonnes of cedarwood oils, mostly from the United States. In Europe, the primary demand is for Chinese cedarwood oil.
 


Table 7.1
Global production of major essential oils from
Cedrus, Cupressus and Juniperus - 1984
 
 
Country
Source of essential oil
Production (Tonnes)
China

India

Kenya

Morocco

USA
 

TOTAL

Cupressus funibris

Cedrus deodara

Juniperus procera

Cedrus atlantica

Juniperus ashei
Juniperus virginiana

450

20

0

7

1400
240

2117

Source: Lawrence (1985).

Essential oils from Cedrus spp.

The genus Cedrus contains four species distributed across Northern Africa, the Near East and the Indian subcontinent and is part of the family Pinaceae (Vidakovic 1991). The essential oils derived from these trees are often considered as substitutes or alternatives to essential oils produced from members of the conifer family Cupressaceae. For this reason, they are discussed with the cedar oils.

In Morocco, the wood of Cedrus atlantica is steam distilled to obtain an essential oil that has a lasting balsamic odour. It is used for scenting of soaps and for fixing of odours. Medicinal uses of this oil include external and internal treatments against bronchitis, tuberculosis, skin diseases and gonorrhoea.

Destructive distillation of C. deodara wood yields a thick tar-like oil. In India, this is used for rubbing on inflated hides commonly used for crossing rivers. It is also a remedy for ulcers and eruptions for mange in horses and sore feet in cattle. This oil is also used to some extent for cremations (Maheshwari and Chhaya Biswas 1970).

Steam distillation of C. deodara wood yields a reddish-brown oil with a characteristic balsamic odour due to the presence of p - methyl - D3 - tetrahydroacetophenone and steam distillation of sawdust yields a pale yellow oil with a pleasant odour and is designated as Himalayan cedarwood oil. The residue, which remains after the distillation of the oil, can be used as a fuel that burns without giving a sooty flame. This oil has been found to be an effective substitute for cedarwood oil from Juniperus virginiana which had been imported into India for manufacture of perfume, scenting soaps, room sprays, disinfectants, etc. It is also used as a tissue-clearing agent in animal and plant histological work and for use with oil emersion lenses. This oil is also suitable for detailed cellular examinations of sections under an oil immersion lens (Maheshwari and Chhaya Biswas 1970).

Production of Himalayan cedarwood oil began in India during the late 1950s (Coppen 1995a) when the Kashmir State drug industry undertook large-scale production of Himalayan cedarwood oil which is now used in large quantities in perfumery and soap industries in place of cedarwood oil Virginiana (Maheshwari and Chhaya Biswas 1970). Twenty years later, production was estimated to be 25 tonnes per year with most of the product being consumed domestically (Coppen 1995a).

In Nepal, an essential oil extracted from the foliage of Cedrus deodara is massaged regularly on affected parts to relieve rheumatic pain (Bhattarai 1992). In the state of Uttar Pradesh, India, oil extracted from the heartwood of C. deodara is used as an insect repellent. It is smeared on the bodies of domestic animals to repel fleas and lice (Singh et al. 1990).
 

ESSENTIAL OILS FROM THE PINACEAE

Several species of the genus Abies, a group of trees well known for their aromatic foliage (Tang Shui Lui 1971) are sources of fragrant essential oils. Most of these oils are extracted from the foliage and are pale yellow to colourless liquids. Balsam fir oil, or fir needle essential oil is a product of A. balsamea, a tree found in eastern Canada and adjoining portions of the United States. This oil is extracted from the foliage by steam distillation. It has a pleasant, fresh, turpentine-like odour and is highly volatile and is used in air fresheners and disinfectants. Huiles Essentielles Branchex Ltd of Quebec, Canada, produces about 4 500 kg of balsam fir oil annually.

Fir Siberian oil is steam distilled from the foliage of A. sibirica, a component of the boreal forests of Siberia and is an ingredient in air fresheners and inhalants. An essential oil is water or steam distilled from the crushed cones of A. alba. This oil is produced in Austria, Germany, Switzerland and Yugoslavia but only on a modest scale. It has a fresh, sweet odour said to resemble bitter orange oil and is used in colognes. In France, an essential oil known as essence de sapin is extracted by volatile solvent extraction from the needles of A. alba. This oil has a fruity balsamic odour that is said to recall the fragrance of a fir forest and is used in bath preparations and leather products (Good Scents Company 1997). Distillation of the foliage of Abies pindrow, a western Himalayan species, yields a pale yellow, aromatic oil with a balsamic odour, which is locally important for scenting soaps, deodorants, disinfectants and inhalants.

Several essential oils are distilled from Pinus spp. These oils are steams distilled from the fresh twigs and needles that have a sweet, evergreen aroma. Pine Norway oil is extracted from Pinus sylvestris, a tree widely distributed across Europe and Siberia. This oil is almost colourless, mobile and has a strong turpentine-like balsamic odour. The dryout characteristic of this oil is of particular interest because there is no odour left on a blotter after 24 hours. It is used primarily in room fresheners, disinfectants, soaps, detergents and vaporizer liquids. Pine mountain oil is a product of the steam distillation of foliage and twigs of Pinus montana, a high elevation European pine. This watery white oil has a slightly spicy odour said to resemble juniper berry oil and is somewhat unique among pine oils in this regard. Mountain pine oil is used in perfumes but can be irritating (Good Scents Company 1997).

Another use for pine oil is in aromatherapy. Pine oil is used in saunas, steam baths and massages to ease the pain of sore muscles.

In Northern Europe, pine oil distillation takes place from spring through winter. The needles and branch tips are gathered when forests are thinned or mature trees are harvested for timber. The mountain forests of the Tyrol area of Austria have a reputation for producing the finest pine oils. Production is not enough to meet world-wide demand, however. Consequently, pine essential oil comes from a variety of locations in Europe and Russia.

Hemlock oil, also known as spruce oil,is steam distilled from the foliage and twigs of the eastern hemlock, Tsuga canadensis, a tree widely distributed across eastern Canada and the United States. The oil is pale yellow or almost colourless and has a pleasant, balsamic, fresh odour with a sweet and slightly fruity cast. This oil is used for room spray perfumes, bath preparations, air fresheners, disinfectants, detergents and other household products (Good Scents Company 1997).

OTHER ESSENTIAL OILS FROM CONIFERS

Sandarac resin produced from Tetraclinis articulata, a small conifer found in Malta, North Africa and Spain, is the source of an essential oil known as sandarac oil. It can be obtained either from steam distillation of sandarac resin or, because the resin acids are soluble in aqueous potassium hydroxide, it can be isolated from a neutralized alcoholic solution of sandarac. The alcohol is evaporated and the alkaline solution is extracted with ethyl ether. After removal of the ether, a small amount of essential oil remains, unaffected by exposure to high distillation temperatures. Sandarac oil is a pale yellow or almost colourless mobile liquid of a turpentine- like, fresh resinous and slightly balsamic odour, which is used as a fixative in woody perfumes, pine fragrances, incense or oriental bases (Good Scents Company 1997).

Araucaria wood oil is steam distilled from the wood of a small tree, Neocallitropsis araucariodes (Synonym Callitropsis araucariodes). This tree is a member of the family Cupressaceae and is endemic to New Caledonia (Vidakovic 1991). The oil is grainy, pale yellow to olive green in colour with a delicate, woody, rich and sweet floral odour. It is used in perfumes (Good Scents Company 1997).

_____________________
16/. Data provided by Huiles Essentielles Branchex Ltd, Quebec, Canada, via the World Wide Web. (http://www.belin.qc.ca/branchex/branchex.htm).
17/. Information provided by Texarome Inc, Leaky, Texas, USA via the World Wide Web.
18/. Information provided by Frontier Cooperative Herbs via the World Wide Web.
19/. Extraction of cedarwood oil in Kenya ended when timber harvesting operations in natural forests was no longer permitted.
20/. Data provided by Dr. M.P. Shiva, Centre of Minor Forest Products, Dehra Dun, India.
21/. Data obtained from Frontier Cooperative Herbs via the World Wide Web

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