Agriculture Reference
In-Depth Information
Fig. 3.8
Structure of glycyrrhizic acid.
Glycyrrhiza glabra is a tall leguminous shrub, the roots of which are
harvested from the wild. Previously, three of the 14 varieties were commercially
important, namely typica grown in southern and central Europe, glandulifera
from central and southern Russia, and violacea grown in Iran and Iraq (Isbrucker
and Burdock 2006). Spain and Turkey are also in the trade. Recently, due to
over-harvesting, Iran has lost signifi cance as a major supplier and China is
now the principal world source, although other species are grown there, namely
G. uralensis and G. pallidifl ora , both somewhat smaller, related plants. Concerned
about desertifi cation, Chinese authorities have begun to restrict licences for both
root collection and the export of liquorice extracts. Prices have moved signifi cantly
upwards in 2010 and are bordering on levels where cultivation is economical.
Techniques for extraction of active components from the root generally include
initial comminution of the root and extraction with hot water and steam. The
primary extract may be concentrated to a paste and cast into blocks or sticks, or
dried to a powder. This crude form contains 10-25% glycyrrhizin.
Commercial processors typically further treat the primary extract with acid to
precipitate glycyrrhizic acid. This is treated with ammonia or other alkalis to
render it soluble. Ammoniated glycyrrhizin is the most common salt, a product of
intense sweetness which possesses the characteristic liquorice fl avour, albeit at
reduced intensity. This may be further refi ned by solvent extraction and separation
techniques to monoammonium glycyrrhizinate.
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Physico-chemical properties
Crude extracts of glycyrrhizin are tan and purifi ed materials are white. Glycyrrhizic
acid is reported as being only sparingly soluble. Ammoniated glycyrrhizin is more
soluble, but there are confl icting reports of the solubility of monoammonium
glycyrrhizinate. For example Hartung (1979) says it dissolves to the extent of
1-2% in water, while Cook (1979) claims only 0.1% at 20°C. The potassium-
magnesium-calcium salt is claimed to dissolve to a solution that is 35% or more
in water (Hartung 1979).
There seem to be no quantitative data on stability in solution published. Use in
acid beverages (below pH 4.5) is diffi cult because of the tendency for the free acid
to precipitate.
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