Chemically, essential oils are a complex mixture of hydrocarbons, alcohols and carbonyl compounds. They are volatile aromatic compounds extracted from aromatic plants. Often terpenes are the most found hydrocarbons and the least found are sesquiterpenes. They are usually concentrated in the bark, flowers, rhizome and seeds of plants. These oils are unrelated to edible oils. They are flammable and soluble in alcohol and ether, but insoluble in water. Obtaining the essential oils occurs from the vegetable tissue by steam drag.


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Extraction of essential oils

Extraction can be performed mechanically or by distillation procedures.  The separation of crude extract and individual components can be done through fractional distillation at reduced haste, crystallization or chromatography. The solvents used are hexane, methylene chloride, acetone, water, vegetable oils and liquid CO2. Subsequently the solvents are removed by distillation. What defines the fact that an extract is an essential oil is the process of obtaining, not its chemical composition. An orange blossom essential oil (neroli essential oil) is obtained by hydro distillation (or steam drag) and contains volatile components. An orange essential oil, obtained by pressing the fruit, followed by centrifugation, contains volatile components (terpenes, esters, aldehydes), but also contains waxes, pigments and flavonoids, among other classes of nonvolatile constituents. Thus, the definition of essential oil is not limited only to the volatility of its composition.

Characteristics of essential oils

– Essential oils for commercial use are mostly a mixture of monoterpene and sesquiterpene hydrocarbons.

– Citrus oil: Citrus fruits orange, lemon, tangerine etc. have a high concentration of essential oil (>3.0%), being commercially obtained as a by-product of juice production. In pressing oil and juice are extracted together and the oil is removed by centrifugation. This oil is widely used in the food, cosmetic and pharmaceutical industry, paints, insecticides, rubbers and veterinary products. Its composition is a mixture of terpenes, sesquiterpenes and oxygenated compounds (aldehydes, acetone, acids, esters, phenols). In industry, terpenes are reduced by a process called desterpenation, with the intention of concentrating the components responsible for the aroma and improving product instability.

– Orange oil: Obtained by cold pressing of the peel, it has a content above 90% limonene.

– Lemon oil: Obtained by cold pressing of the peel, it has terpenes as the main component. The limonene content reaches 75% of the total oil. Its odor differentiates it by the presence of citral (neral and geranial).  Limonene is very sensitive to oxidation.

– Aniz oil: Obtained from dried seeds and consisting essentially of anetole (trans-1-p-methoxyphenol-propien).

– Fennel oil: Obtained from seeds has as main components the carvone and limonene.

– Mint oil: Obtained by dry leaves and stalks, it has as main component the cyclic oxygenated monoterpenes menthel and menth name, being the menthel responsible for flavor and refreshing odor.

– Rosemary oil: Obtained by rosemary leaves, it is widely used in the perfumery industry.

References

– ARAUJO, Julio Maria A. Chemical food.- Sc
ielo: “Phytotherapy in today’s world-
Costa, A.F. Pharmacognosy. Lisbon, Calouste Gulbenkian Foundation, 1977, volume I

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