Page 24 - Medicinal Plants_PharmD general

Drying is the most common and fundamental method for post-
harvest preservation of medicinal plants. The method of drying is selected
depending on the type of chemical constituents in the plant. Different
methods of drying are:

1. Natural Drying

(a) Sun-Drying
In case of natural drying, it may be either direct sun-drying or in
the shed. If the natural colour of the drug (digitalis, clove, senna)
and the volatile principles of the drug (peppermint) are to be
retained, drying in the shed is preferred. If the contents of the
drugs are quite stable to the temperature and sunlight, the drugs
can be dried directly in sunshine (gum acacia, seeds and fruits).

(b) Air drying
Materials are dried with unheated forced air, taking advantage of
its natural drying potential. The process is slow and weather-
dependent, so a wise strategy "fan off-fan on" must be devised
considering the following conditions: Air temperature, relative
humidity and moisture content and temperature of the material
being dried.

2. Mechanical (Artificial) Drying

Drying by mechanical and artificial means includes (a) oven drying;
i.e. tray-drying; (b) vacuum drying, (c) microwave vacuum drying (d)
spray drying and (e) freeze drying

(a) Oven (tray) drying (Figure 3a)

The drugs which do not contain volatile oils and are quite stable to
heat or which need deactivation of enzymes are dried in tray dryers.
In this process, hot air of the desired temperature is circulated

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