Different methods of secondary metabolite, essential oil extraction and estimation
Distillation, as the most important process for obtaining essential oils, needs
attention first. It may be defined as the "separation of the components of a mixture of two
or more liquids by virtue of differences in their vapour pressure"
(i) Water Distillation
When this method is employed, the material to be distilled comes in direct contact
with the boiling water. It may float on the water or be completely immersed, depending
on its specific gravity. The water is boiled by application of heat by any of the usual
methods, i.e., direct fire, steam jacket, closed steam coil, etc. Through this method,
powdered materials like almond and others like rose petals and orange blossoms are
Disadvantages of Water Distillation
1. If the temperature is high, there will be browning of the essential oil.
2. In this method, certain compounds like esters are partly hydrolyzed.
3. It requires a greater number of stills, more space and more fuel.
4. It demands considerable experience and familiarity to successfully use this method.
(ii) Water and Steam Distillation
In this case, the plant material is supported on a perforated grid or screen inserted
at some distance above the bottom of the still, and the lower part of the still is filled with
water to a level below the grid. The water is heated. The typical features of this method
are: first, that the steam is always fully saturated, wet and never super-heated; second,
that the plant material 'is in contact with the steam only and not with the boiling water.
This method gives best results with materials like seeds and roots.
Disadvantages of Water and Steam Distillation
1. To obtain the best results, it is necessary that the charge should be in homogenous
2. If the material is extremely wet, it results in lumping or agglomeration of the charge.
3. It takes a comparatively long time for distillation.