Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS
5
Decoction and Hot Continuous
Extraction Techniques
Abstract
S. Tandon and S. Rane
The chapter describes the techniques, parameters and equipment used for the extraction
of plants by decoction and hot continuous extraction. Principles, mechanisms,
merits and demerits of conventional solvent extraction and accelerated solvent extraction
are also discussed.
5.1 Introduction
Of the traditional methods of extraction of medicinal plant material
for making an aqueous extract, decoction is one of the most described.
Decoction is a water-based preparation to extract active compounds from
medicinal plant materials. In this process, the liquid preparation is made
by boiling the plant material with water. Decoction differs from infusion in
that the latter is not actively boiled. Decoction is the method of choice
when working with tough and fi brous plants, barks and roots and with plants
that have water-soluble chemicals. The plant material is generally broken
into small pieces or powdered. Different methods have been described for
the preparation of decoctions. In the Ayurvedic method, traditionally known
as kwatha, the crude drug in form of yavakuta (small pieces) is placed in
earthen pots or tinned copper vessels with clay on the outside. Water is
added and the pot is heated on a fi re. If the material is soft, four times water
is used per 1 part drug; if the drug is moderately hard, eight times water is
used and if the drug is very hard, sixteen times water is recommended. The
mixture is then boiled on low fl ame until it is reduced to one-fourth starting
volume, in case of soft drugs, and one-eighth in case of moderately or very
hard drugs. The extract is then cooled and strained, and the fi ltrate is collected
in clean vessels.
5.2 Solid-liquid Extraction Process
Solid-liquid extraction is one of the most widely used unit
operations in the medicinal and aromatic plant industry. One example of
solid-liquid extraction is the solvent extraction of herbs. This process, also
referred to as leaching, is a separation technique that is often employed
to remove a solute from a solid mixture with the help of a solvent. The insoluble
solid may be colossal and permeable; more often it is particulate
and the particles may be openly porous, cellular with selectively permeable
cell walls, or surface-activated. The stream of solids being leached and the
accompanying liquid are known as the underfl ow. The solid content of the
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