The application of natural hydrocolloids to foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 184

heating can be used during food processing to produce thermally stable gels.
These gels are insoluble in water (even boiling water) and can be retorted.
The high molecular weight of konjac accounts for the gum's high viscosity in
solution, making it a good thickener for food products. However, its relatively
high cost means that konjac gum is rarely used for its thickening properties alone.
However, konjac acts synergistically with xanthan to give an increased viscosity.
At higher levels of konjac, a thermally reversible, strong, elastic gel will be
formed with xanthan. These gels are very freeze-thaw stable and have low
syneresis. Such gels can also be formed with mixtures of konjac and carrageenan
(showing stronger synergy than carrageenan and LBG). The texture of the gel can
be changed by varying the gum ratio.
Noodles made from konjac are a traditional food in Asia. They are made by
heating glucomannan solutions with limewater to form a thermally stable gel,
which is cut into thin strips and used as a meal component. This thermally
stable gel is also used in meat, seafood and vegetarian products for moisture
binding and texture control. Konjac gum is used in conjunction with carrageenan
in table jellies and aspics to give the desired fi rm but elastic texture. Its good
freeze-thaw stability and control of ice crystal growth makes it a popular gum
for use in surimi, and also ice cream and other frozen desserts. Like other
hydrocolloids, it is a good thickener and stabiliser for some beverages (for
example juice drinks), sauces and dressings. It is widely used in the applications
described above in Asia.
Konjac is approved for use in all the major countries in the world, though there
was an unfortunate episode soon after its approval in Europe. Konjac is used in
the production of fruit jelly confectionery cups, a very popular product in Asia.
However, it was alleged that there were incidents of children choking on them in
the UK, due to their specifi c shape and not necessarily due to the presence of
konjac gum, which resulted in an import ban in 2004 (EC 2004). Konjac is
permitted as a food additive in general foodstuffs in Europe, but with an
amendment to prevent its use in jelly confectionery.
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8.3.5 Gum arabic
There are three tree exudates gums used in the food industry - acacia (gum arabic),
tragacanth and karaya. Acacia gum is the most widely used. Gum arabic is the
gummy exudate produced by Acacia Senegal and Acacia Seyal trees, which grow
widely across the Sahelian belt of Africa, particularly from Senegal to Somalia
(Williams and Phillips 2009b). Gum production is stimulated by making a
transverse incision in the bark of the trunk and peeling off a strip of bark. The gum
exudes into pale yellow/orange balls the size of a tennis ball, which harden rapidly
by evaporation. These balls are collected by hand, cleaned of any loose detritus,
and sorted according to colour and size. Mechanical grinding is used to break up
the balls of gum to speed up dissolution in water, which is the next stage. After
removing any insoluble material by fi ltration, the solution is pasteurised and then
spray or roller dried.