Page 25 - Medicinal Plants_PharmD general

through the dryers and this facilitates the removal of water content
of the drugs. Belladonna roots, cinchona bark, tea and raspberry
leaves and gums are dried by this method.

(b) Vacuum drying (Figure 3b)
The hygroscopic drugs which are sensitive to higher temperature are
dried by this process, e.g. Tannic acid and digitalis leaves. The
moisture present in a substance, usually a wet solid, is removed by
means of creating a vacuum. With the help of vacuum pumps, the
pressure is reduced around the substance to be dried. This decreases
the boiling point of water inside that product and thereby increases
the rate of evaporation significantly.

(c) Microwave vacuum drying (Figure 3c)
Microwave energy combined with a vacuum environment for rapid
low temperature dehydration to produce high quality products.

(d) Spray drying (Figure 3d)
Few drugs which are highly sensitive to atmospheric conditions and
also, to the temperature of vacuum drying are dried by spray drying
method. Examples are papaya latex, pectin, tannins, etc. It is a
method of producing a dry powder from a liquid by rapidly drying
with a hot gas. This is the preferred method of drying of many
thermally-sensitive materials. Air is the heated drying medium used;
however, if the liquid is a flammable solvent such as ethanol or the
product is oxygen-sensitive then nitrogen is used.

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