Extraction Technologies For Medicinal And Aromatic Plants - Unido

EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS
d) In case of hot extraction, higher than required temperature
should be avoided. Some glycosides are likely to
break upon continuous exposure to higher temperature.
e) Standardization of time of extraction is important, as:
Insuffi cient time means incomplete extraction.
If the extraction time is longer, unwanted constituents
may also be extracted. For example, if tea is boiled
for too long, tannins are extracted which impart astringency
to the fi nal preparation.
f) The number of extractions required for complete extraction
is as important as the duration of each extraction.
vii) The quality of water or menstruum used should be specifi ed
and controlled.
viii) Concentration and drying procedures should ensure the safety
and stability of the active constituents. Drying under reduced
pressure (e.g. using a Rotavapor) is widely used. Lyophilization,
although expensive, is increasingly employed.
ix) The design and material of fabrication of the extractor are
also to be taken into consideration.
x) Analytical parameters of the fi nal extract, such as TLC and
HPLC fi ngerprints, should be documented to monitor the
quality of different batches of the extracts.
1.2.2 Steps Involved in the Extraction of Medicinal Plants
In order to extract medicinal ingredients from plant material,
the following sequential steps are involved:
1. Size reduction
2. Extraction
3. Filtration
4. Concentration
5. Drying
1.2.2.1 Size Reduction
The dried plant material is disintegrated by feeding it into a
hammer mill or a disc pulverizer which has built-in sieves. The particle size
is controlled by varying the speed of the rotor clearance between the hammers
and the lining of the grinder and also by varying the opening of the
discharge of the mill. Usually, the plant material is reduced to a size between
30 and 40 mesh, but this can be changed if the need arises. The
objective for powdering the plant material is to rupture its organ, tissue and
cell structures so that its medicinal ingredients are exposed to the extraction
solvent. Furthermore, size reduction maximizes the surface area, which
in turn enhances the mass transfer of active principle from plant material
to the solvent. The 30-40 mesh size is optimal, while smaller particles may
become slimy during extraction and create diffi culty during fi ltration.
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