Extraction (Preparation of Volatile Oils)

2.6.1.3 Extraction 

The extraction process is particularly useful for such plant sources which either contain very small amount of volatile oils or the oil contents are extremely succeptible to decomposition by the exposure to steam. In such cases the recovery of volatile oils is not commercially feasible.

Examples: Volatile oils obtained from various flowers like Jasmine (Jasminum officinale Linn. Ver grandiflorum Bailey: family – Oleaceae); Sweat violet (Violaodorata Linn, family – Violaceae);

Gardenia (Gardenia lucida Roxb., family – Rubiaceae); Acacia (Acacia farnesiana Willd., family–Leguminosae); Narcissus (Narcissus tazetta Linn., family –Amaryllidaceae); and Mimosa (Mimosa pudia Linn., family – Leguminosae).

In general, the extraction of volatile oil from natural sources is carried out by two different methods, namely:

(i) Extraction with volatile solvents e.g., Hexane, Benzene and

(ii) Extraction with non-volatile solvents e.g., Tallow, Lard, Olive oil

These two extraction processes shall be discussed briefly in the sections that follows:

2.6.1.3.1 Extraction with Volatile Solvents The plant material containing the volatile oil is usually extracted with a low boiling volatile solvent, such as n-hexane, benzene, petroleum ether etc., either by adopting the method of hot continuous extraction (Soxhlet extraction) or by percolation.

The resulting volatile oil containing solvent is removed under reduced pressure when the volatile oil will remain in the flask.

Advantages There are several advantages of this process, namely:

1. It is possible to maintain an uniform temperature (usually 50oC) during most of these extractions which ultimately ensures the retention of a more intense and natural fragrance which otherwise cannot be achieved by distillation (perhaps due to chemical degradation of constitutents).

2. Floral Concretes: The ultimate concentrated and purified volatile oils are collectively designated as ‘floral concretes’. In actual practice, these floral concretes represent an admixture of natural odoriferous components of flowers, plant waxes, colour pigments and certain albuminous material. Hence, most of them are solid in consistency and partly soluble in 95% alcohol.

2.6.1.3.2 Extraction with Non-Volatile Solvents This process is usually employed for the

preparation of the finest brands of perfume oil i.e., the natural flower oils. In this instance, the volatile oil content usually present in the fresh plant sources eg., flower petals, is so scanty that oil removal is not commercially viable by any other methods. Grassein Southern France, is the wellknown centre for the extraction of flower volatile oil in the world.

There are three methods that are used for the extraction of volatile oils from flowers with nonvolatile solvents, namely:

(i) Enfleurage Method,

(ii) Pneumatic Method, and

(iii) Meceration Method.

These methods would be described briefly as under.

(a) Enfleurage Method: A thick layer of molten lard and tallow (beef fat) is applied on either surfaces of pre-cleaned glass plates that are securedly placed in a covered wooden frame (or the chasis) Each glass plate is liberally sprinkled with fresh flower petals to cover its top surface only. These plates are now stacked one over the other and enclosed in the wooden frame, whereby each layer of the flower shall be enclosed between two layers of the fat. Such batteries of loaded plates are allowed to remain for 24hours, after which the flowers are removed and recharged with fresh lots. This very process is repeated religiously for several weeks till the fatty layers appear to be fully saturated with the essential oils of the flowers or until a certain desired concentration of it is accomplished.

Example: Jasmine flowers—The whole process lasts nearly seventy days.

The flowers are subsequently removed (defleurage) and the fat is separated carefully and stirred with absolute alcohol. The latter will dissolve the volatile oil portion thereby leaving the former undissolved in alcohol. The alcoholic extract is reasonably chilled and filtered to get rid off any traces of residual fat. Three successive extraction procedures are repeated so as to affect the complete recovery of volatile oil and the resulting solution is employed as such in the perfume industry and is commonly termed as the ‘Tripple Extract’.

The volatile oil may be recovered from the ‘Triple Extract’ by anyone of the following methods, namely: first, fractional distillation under vacuum at 0^oC; secondly, evaporation under vacuum at 0^oC; thirdly, the alcoholic extract is diluted with water and saturated with NaCl, when the oil will seaparate with the retention of fresh natural ordour.

(b) Pneumatic Method: The basic principle of this method is very much like the ‘enfleurage method’. In this particular instance, the current of warm-air is made to pass through the flowers , and the subsequent air loaded with suspended volatile oil particles is then routed through a fine spray of molten fat in a closed chamber wherein the volatile oil gets absorbed promptly, and

(c) Maceration Method: The fresh flower petals are gently and carefully heated in molten fat (lard, tallow, or fixed oil), stirred frequently until complete exhaustion takes place. The flowers are then strained, squeezed and the exuded fat is returned to the main bulk of the fat, unless and until a desired concentration is achieved. The volatile oil containing fat is allowed to cool and is recovered by three successive extractions with absolute alcohol.

Source:Pharmacognosy And Pharmacobiotechnology By Ashutosh Kar