METHODS EMPLOYED TO OBTAIN VOLATILE OILS

Volatile oils are usually obtained by following different methods, depending upon the conditions of the plant material.

1. DISTILLATION:

a. Water distillation.

b. Water steam distillation.

c. Steam distillation.

2. Expression:

3. Enfleurage method.

4. Enzymatic hydrolysis.

5. Solvent extraction.

6. Destructive distillation.

1. DISTILLATION:

a. Water distillation:

This method is applied to plant material where there is no chance of injuries by boiling. Turpentine oil is obtained by this method. The material is placed in distillation chamber along with water and subjected to heat until volatile matter, both water and oil is condensed in the condensing chamber. This is a special type of receiver having two outlets; one at the bottom and other at the top. If volatile oil is heavier than water, it is separated from below. If it’s lighter than water, it is separated from upper outlet.

b. Water and steam distillation:

This method is employed when there is chance of destruction of volatile oil by boiling, or it is obtained from dry of fresh substance.

In case of dried material e.g. cinnamon or clove, the drug is ground and then covered with a layer of water. Steam is passed through the macerated mixture. Because the oil could be impaired by direct heating, the steam is generated else where and us piped into the container holding the drug.

The oily layer of the condensed distillate is separated from the aqueous layer.

c. Direct steam distillation:

This method is applied to fresh plants drugs e.g. peppermint or spearmint etc. The crop is cut and placed directly into a metal distillation tank on a truck bed. The truck is driven to distilling tank. The plant material is still green and contains considerable natural moisture, therefore maceration is necessary.

Steam is forced through the fresh herb which carries the droplets through a vapour pipe attached at the top of the tank to the condensing chamber.

During steam distillation certain components of a volatile oil tends to hydrolyze, where as other constituents the high temperature decomposes. In order to avoid it, the diffusion rate of steam and water through plant membrane should be highest as to keep the hydrolysis and decomposition at a minimum.

d. Destructive distillation:

Destructive distillation is a mean of obtaining empyreumatic oils.

When the wood or resin of membrane of the Pinaceae is heated without access of air, decomposition takes place and a no of volatile components are driven off. The resultant mass is charcoal. The condensed volatile matter usually separated into two layers.

An aqueous layer containing wood naphtha (methyl alcohol) and pyroligenous acid (crude acetic).

Other layer is tarry liquid in the form of pine tar, Juniper tar, or other tars depending upon the wood introduced.

This dry distillation is usually conducted in retorts and if the wood is chipped or coarsely ground and the heat applied rapidly the yield of tar represents about 10% of the wood used.

2. EXPRESSION AND ECUELLE METHOD:

Mostly the citrus oil is obtained by this method. This is a mechanical method in which fruits are rolled over a trough lined with sharp projections just long enough to penetrate the oil glands present in the fruits.

The droplets are collected in trough and finally separated. This method is used avoid the decomposition of volatile oils, which will necessarily take place by any other distillation method.

3. ENZYMATIC HYDROLYSIS:

Glycosidic volatile oils like bitter almond, mustard oil is obtained by enzymatic hydrolysis of glycosides. In bitter almond seeds amygdalin is acted upon by enzyme emulsin resulting in a mixture of constituents from which the volatile oil may be distilled with steam. In black mustard seeds the glycoside, sinigrin is hydrolysed by the enzyme myrosin with the product of volatile mustard oil.

4. ENFLEURAGE:

This method is especially used for those volatile oils, which are present in such a part which is very small and also liable to decomposition on distillation. In this case odourless and bland fixed oil or fat is spread in a thin layer on glass plates. The part of plant from which V.O has to be extracted say for example flower petal is placed in the fat or fixed oil for some time until its fragrance is removed as the oil or fat will absorb it. Then the petal is removed from the fixed oil or fat and is subjected to extraction with alcohol. This method not in practice as it is tedious and time consuming.

5. EXTRACTION BY SOLVENT:

This is very costly method and is mostly used in perfume industry. The parts containing volatile oil are extracted directly by one of the organic solvents and they are then separated.