Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

4 HYDROLYTIC MACERATION, EXPRESSION AND COLD FAT EXTRACTION
of solvent through the powdered drug. The rate of extraction depends upon
the following:
• The rate of transport of solvent into the mass to be leached.
• The rate of solubilization of soluble constituents into solvent.
• The rate of transport of solute out of the insoluble material
and from the surface of the insoluble material into the solution.
In the process of maceration, the powered solid material is
placed in a closed vessel (to prevent evaporation) and the chosen solvent
(menstruum) is added. It is allowed to stand for a long time (varying from
hours to days) with occasional shaking. Suffi cient time is allowed for the
menstruum to diffuse through the cell wall to solubilize the constituent
present in the cells and for the resulting solution to diffuse out. The process
takes place only by molecular diffusion. After the desired time, the
liquid is strained off; the solid residue (marc) is pressed to recover as
much solvent as possible. When the menstruum is water and the period
of maceration is long, a small quantity of alcohol may be added to prevent
microbial growth.
Cold maceration of crushed grapes is done at room temperature
before the onset of fermentation. In this process, the skin and seeds
are permitted to soak for one to two days prior to the initiation of fermentation
to get more aqueous extraction without the effect of ethanol on grape
cells. In certain cases, hydrolysis is done with a suitable agent (enzyme)
prior to maceration, e.g. maceration of wine. The quality of wine is judged
by its appearance, color, aroma, taste (mouth feel) and fl avor. Grape-derived
aroma and fl avor precursors exist partially as non-volatile, sugar-bound glycosides.
Hydrolysis modifi es sensory attributes and potentially enhances
wine quality. Flavored aglycones potentially affect the wine quality after hydrolysis.
Cell wall-degrading enzymes help in the release of grape aroma,
when cold maceration prior to fermentation has been carried out.
4.3 Expression Extraction of Essential Oils
Most essential oils are isolated from the respective plant parts
by the process of hydrodistillation or steam distillation. A few essential oils
such as those present in the citrus fruit peel can be, and in large part are,
obtained by pressing, which yields a product of superior quality. The long
action of heat with boiling water affects some thermolabile constituents
which may decompose due to hydrolysis, polymerization and resinifi cation.
Therefore, the essential oil obtained by distillation does not represent the
natural oil as it originally occurred in the plant material. In such plant materials,
essential oil is extracted by the process of expression or solvent
extraction.
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