Extraction Technologies For Medicinal And Aromatic Plants - Unido

3.7 Infusion
3.7.1 General Considerations
EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS
Infusions are dilute solutions containing the readily soluble
constituents of crude drugs. Formerly, fresh infusions, prepared by macerating
the drug for a short period in cold or boiling water, were used and diluted
to eight volumes but, now, infusions are usually prepared by diluting one
volume of a concentrated infusion to ten volumes with water. Concentrated
infusions are prepared by a modifi ed percolation or maceration process.
After dilution with water, concentrated infusions resemble in potency and
aroma the corresponding fresh infusion. Infusions are liable to fungal and
bacterial growth, and it is necessary to dispense them within 12 h of their
preparation.
3.7.2 General Method for Preparing Fresh Infusions
The coarsely powdered crude drug (50 g) is moistened, in a
suitable vessel with a cover, with 50 ml cold water and is allowed to stand
for 15 min. Then, 900 ml boiling water is added, and the vessel is covered
tightly and allowed to stand for 30 min. The mixture is strained and enough
water is passed to make the infusion measure 1000 ml. Some drugs are
supplied (accurately weighed) in muslin bags for preparing specifi c amounts
of infusion and as such are used for infusion preparation. If the activity of
the infusion is affected by the heat of the boiling water, cold water should be
used. As fresh infusions do not keep well, they should be made extemporaneously
and in small quantities at the time of use.
3.7.3 Preparation of Concentrated Infusions
The offi cial monographs also recognize certain “concentrated
infusions” in which 25% alcohol is added during or after the infusion process
and then diluted as per pharmacopoeial (offi cial) requirement. Concentrated
infusions are especially prepared in cases in which the active and desirable
principles of drug are equally soluble in water and in the menstruum used
for both concentrates and infusions.
3.8 Evaporation
One quality-relevant parameter is the evaporation of the eluate
from the soft extract. The state of art is cautious vacuum evaporation, in
which evaporation temperatures do not exceed 55° C. The temperature in
relation to the evaporation time is of special importance for quality of this
step, especially if the extract contains volatile or thermolabile constituents.
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