Volatile Oils (Etheral oil/Essential Oil)
•Volatile or essential oils, as their name implies, are volatile in steam.
•They differ entirely in both chemical and physical properties from fixed oils.
•They are secreted in oil cells, in secretion ducts or cavities or in glandular hairs.
•They are frequently associated with other substances such as gums and resins and themselves tend to resinify on exposure to air.
Production & uses Of Volatile Oil
The total annual production of volatile oil is estimated to be in the region of 45,000 tonnes worth approximately US$700 million.
There are about 100 commercially valuable volatile oils directly derived from plants.
Volatile Oils are used for their therapeutic action,for flavouring (ex-oil of lemon),in perfumery (ex-oil of rose) or as starting material for the synthesis of other compounds (ex-oil of turpentine).
•For therapeutic purposes they are administered as inhalations (e.g. eucalyptus oil), orally (e.g. peppermint oil), as gargles and mouthwashes (e.g. thymol) and transdermally (many essential oils including those of lavender, rosemary and bergamot are employed in the practice of aromatherapy).
•Those oils with a high phenol content, e.g. clove and thyme have antiseptic properties, whereas others are used as carminatives. Oils showing antispasmodic activity, and much used in popular medicine
•Volatile or essential oils, as their name implies, are volatile in steam.
•They differ entirely in both chemical and physical properties from fixed oils.
•They are secreted in oil cells, in secretion ducts or cavities or in glandular hairs.
•They are frequently associated with other substances such as gums and resins and themselves tend to resinify on exposure to air.
Production & uses Of Volatile Oil
The total annual production of volatile oil is estimated to be in the region of 45,000 tonnes worth approximately US$700 million.
There are about 100 commercially valuable volatile oils directly derived from plants.
Volatile Oils are used for their therapeutic action,for flavouring (ex-oil of lemon),in perfumery (ex-oil of rose) or as starting material for the synthesis of other compounds (ex-oil of turpentine).
•For therapeutic purposes they are administered as inhalations (e.g. eucalyptus oil), orally (e.g. peppermint oil), as gargles and mouthwashes (e.g. thymol) and transdermally (many essential oils including those of lavender, rosemary and bergamot are employed in the practice of aromatherapy).
•Those oils with a high phenol content, e.g. clove and thyme have antiseptic properties, whereas others are used as carminatives. Oils showing antispasmodic activity, and much used in popular medicine
Volatile oils are secreted in special structures like duct cells, schizogenous or lysogenous glands, trichomes and vittae etc. These are commonly found in the families like:
Labiatae: e.g. Oscimum sanctum, Mentha
Zingiberaceae: e.g. Cardamom, Ginger
Umbelliferae: e.g. Coriander, Fennel, Caraway, Cumin
Myrtaceae: e.g. Clove, Eucalyptus
Lauraceae: e.g. Cinnamon
Graminae: e.g. Lemon grass
Composition Of Volatile Oil
•Volatile oils are generally mixtures of hydrocarbons and oxygenated compounds derived from these hydrocarbons.
•The odour and taste of volatile oils is mainly determined by these oxygenated constituents, which are to some extent soluble in water but more soluble in alcohol.
•Practically all volatile oils consist of chemical mixtures that are often quite complex; they vary widely in chemical composition.
•Almost any type of organic compound may be found in volatile oils (hydrocarbons, alcohols, ketones, aldehydes, ethers, oxides, esters, and others). “usually volatile oils are classified according to the type of organic compounds”.
•It is not uncommon for a volatile oil to contain over 200 components, and often the trace constituents are essential to the odor and flavor. The absence of even one component may change the aroma.
Biosynthesis
•Chemical constituents of volatile oils may be divided into 2 broad classes, based on their biosynthetic origin:
1.Terpene derivatives formed via the acetate-mevalonic acid pathway.
2.Aromatic compounds formed via the shikimic acid-phenylpropanoid route.
Terpene derivatives
Aromatic Compounds
Physical property
•Although volatile oils differ greatly in their chemical constitution, they have a number of physical properties in common:
1.They possess characteristic odors.
2.They are characterized by high refractive indices.
3.Most of them are optically active.
4.Their density is generally lower than that of water (the essential oils of sassafras, clove, or cinnamon are the exceptions).
•As a rule, volatile oils are immiscible with water, but they are sufficiently soluble to impart their odor to water. The aromatic waters are dependent on this slight solubility.
Chemical Test
1.Thin section of drug on treatment with alcoholic solution of Sudan Red -III develops red color in the presence of volatile oils.
2.Thin section of drug is treated with tincture of alkana, which produces red color that indicates the presence of volatile oils in natural drugs.
Difference Between Volatile oils And Fixed Oils
•Several points of differentiation exist between volatile oils and fixed oils.
1.Volatile oils can be distilled from their natural sources.
2.Volatile oils do not consist of glyceryl esters of fatty acids. Hence, they do not leave a permanent grease spot on paper and cannot be saponified with alkalies.
3.Volatile oils do not become rancid as do the fixed oils, but instead, on exposure to light and air, they oxidize.
Isolation
1.Expression method: By this method generally oil of fruit are separated by crushing like citrus
and lemon.
2.Steam distillation/hydro distillation: Usually the volatile oil, which is less affected by heat, is isolated by this method. In this method plant material is either macerated with H2O or directly passed with steam and the essential oil obtained in distillate is extracted with organic volatile solvent like petroleum ether.
3.Solvent extraction: This is very widely used extraction method in perfume industry for the production of volatile oil using lipid solvent like ether or benzene. This is very economical as there are very less deterioration of volatile oil and solvent is distilled off.
4.Enflurage method/adsorption on purified fat: This is very old method and still used now days generally flowers petals are strain on the surface of a glass plate having a layer a purified fat and maintained at temperature of 50 oC. The petals are kept in contact with fat for few days their wax is separated, digested with ethanol and cooled at 20 oC to remove fat. The alcohol is then removed by distillation under reduced pressure.
5.Supercritical fluid method: At certain critical pressure and temperature the gasses behaves like a liquid, which diffuse well through solids and acts as good solvent. The gasses like CO2 are chemically inert, non-inflammable, nontoxic, easy to eliminate, selective, readily available and do not cause any hydrolysis or rearrangement of component to be extracted. Hence, in spite of high cost this method is enormously spreading for supercritical fluid to liquid-liquid extraction. Now days this method is used for production of decaffeinated coffea, nicotinless tobacco products and terpenless oils.
Use of Drugs containing Essential Oil
•Pharmacy
•Perfumery
•Food technology
•Miscellaneous industries (as starting materials for the synthesis of the active principles of medicines, vitamins, and fragrances).