The application of natural hydrocolloids to foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 186

major growing regions of Sudan. This has led to dramatic fl uctuations in price and
an increased interest in fi nding alternative hydrocolloids with the desired
functionality. Modifi ed starches have been developed to replace gum arabic's
emulsifying function in fl avour oil emulsions for beverages, but these do not meet
the natural hydrocolloid criteria. Starches and other gums (typically pectin,
gelatin or agar), usually in blends, have been more successful in partially or
completely replacing gum arabic in confectionery, but care has to be taken to
ensure that de-mixing does not occur due to incompatibility between the various
hydrocolloids.

8.3.6 Gum karaya and gum tragacanth
Although gum arabic is by far the most important plant exudate, there are other
natural exudate gums in use in the food industry, which have been used for
centuries in their local markets.
Tragacanth is collected from the Astragalus gummifer and Astragalus
microcephalus shrubs grown mainly in arid regions of Iran and Turkey. Gum is
produced by incisions in the lower stem and root. The exudate is allowed to dry
on the shrub before collection and is produced in two forms - ribbons and fl akes.
After collection, the gum is graded and milled to a powder. The best grades
produce the highest viscosity gum, with the least solution colour, and the lowest
microbiological contamination. In practice, most food applications use mixed
ribbon or fl ake grades to give the required viscosity.
Tragacanth is a complex branched polysaccharide consisting of two main
fractions. The major fraction (known as bassorin or tragacanth acid) is not soluble
but swells in water to form a gel. The second fraction (tragacanthin) is water-
soluble. Like gum arabic, tragacanth contains a small amount of protein (1-4%),
which may be involved in its emulsifying properties.
Tragacanth is an effective thickener, giving high viscosity at low concentrations.
It is unusual in that it possesses both thickening and emulsifying properties.
Add to this its excellent acid stability (down to pH 2) makes it ideal for use in
the production of dressings, both pourable and spoonable. However, cost and
quality considerations have meant that xanthan has mostly replaced gum
tragacanth in these applications. Tragacanth improves the handling and sheeting
properties of icing, so is commonly used in confectionery icing. It is the traditional
binder for sugarcraft icing, used to create edible cake decorations such as
fl owers.
Karaya gum is another tree exudate, this time collected from Sterculia urens , a
large bushy tree. The main growing areas are India and West Africa. Incisions are
made in the bark of the tree, the gum exudate is allowed to dry before collecting,
sorting by colour and then milling to a powder. Different grades are classifi ed by
colour, particle size and viscosity.
Karaya gum is a branched anionic polysaccharide used as a thickener (cold
water swelling, in a similar fashion to starch). It has good acid stability and is a
useful thickener since it does not have the 'gummy' texture associated with many

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