Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

5 DECOCTION AND HOT CONTINUOUS EXTRACTION TECHNIQUES
stream is called marc. The stream of liquid containing the leached solute is
known as the overfl ow.
5.3 Process Parameters Affecting Solid-liquid
Extraction
The following parameters generally affect the rate of solid-liquid
extraction (leaching):
• Post-harvest processing
• Matrix characteristics
• Choice of solvent
• Method of contact
• Temperature of extraction
• Number of washes
• Condition for extraction (e.g. agitation)
5.3.1 Post-harvest Processing
After harvesting, most herbs have a moisture content of
60%-80% and cannot be stored without drying. Otherwise, important compounds
can breakdown or micro-organisms may contaminate the material.
Drying of the herbs in shade in a thin layer is generally preferred. Some
medicinal plants, like pyrethrum, lose their active constituents if exposed to
direct sun light for a long period. For drying large quantities of plant material,
a hot air drying oven is used where material can be placed on a large
number of trays stacked over each other. Oven temperature must be kept
at a safe level so as not to damage the active constituents of the medicinal
plant.
5.3.2 Matrix Characteristics
Knowledge of the matrix characteristics of the carrier solid is
important to determine whether it needs prior treatment to make the solute
more associable to the solvent. Grinding of plant material means mechanically
breaking down leaves, roots, seeds, or other parts of a plant into small
units, ranging from large course fragments to fi ne powder.
Solute may exist in the inert solids in a variety of ways:
1. On the surface of the solid,
2. Surrounded by a matrix of inert material, Chemically combined,
or inside the cells.
Solute adhering to the solid surface is readily removable by
solvent. When the solute exists in pores surrounded by a matrix of inert
material, the solvent has to diffuse to the interior of the solid to capture the
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