Gum Karaya is the dried
exudate of the Sterculia Urens tree of the Sterculiaceae
family. This large and bushy deciduous tree is found in
the dry deciduous forests of the Indian Peninsula, the
rocky hills of Madhya Pradesh and Bihar and the
sub-Himalayan tract in northern India. The tree is
leafless in the cold season; young leaves sprout in the
The best quality gum is collected during April, May and
June i.e. in summer. During this time, as the weather
gets warmer the yield increases. The gum collected
during the monsoons has low viscosity. In September,
after the monsoon, the collection cycle is repeated.
This yield usually gives less viscous solutions than the
gum collected in summer.
Incision on the trunkThe locals tap the trees by making
incisions upto one square foot in dimension on the
trunk. The gum begins to exude immediately and the
exudation continues for several days. The maximum amount
of exudation occurs within the first 24 hours. The gum
is in the form of huge irregular tears. The tears are
picked by the locals who sell the same to the forest
contractors registered with the Trifed. In the state of
Andhra Pradesh, the purchases of raw Gum Karaya are
centralized through the state owned Girijan Co-operative
Then the gum is sold to Gum Karaya associate shippers
like Krystal Colloids Pvt. Ltd. who process the lots after basic
tests for the swell index. Bark and other contaminants
are first removed. The tears are then broken up and the
fragments are sorted into grades on the basis of colour
and adhering bark.
The grades and their technical specifications are as
AT 1 %
with slight gray cast
Gum Karaya occurs naturally as a complex, partially
acetylated, branched polysaccharide of high molecular
weight. It contains about 37% uronic acid residues and
approximately 8% acetyl groups. The gum has a peculiar
property of splitting off free acetic acid and this loss
is loosely correlated with the particle size. Karaya is
a calcium and magnesium salt, with a central chain of D-galactose,
L-rhamnose and D-galacturonic acid units, with some side
chains containing D-glucuronic acid.
Although designated as a water- soluble gum, Karaya is
one of the least soluble of the exudation gums. A gum
particle placed in water does not dissolve but absorbs
water and swells to many times its original size. The
particle size influences the type of the dispersion
obtainable. A coarse granulated Karaya yields a
discontinuous, grainy dispersion; a finely powdered gum
yields an apparently homogenous dispersion. In dilute
solutions of Gum Karaya, the viscosity increases
linearly with concentrations up to about 0.5%,
thereafter Karaya dispersions behave as non-Newtonian
solutions. At concentrations above 2-3% Gum Karaya forms
thick, non-flowing pastes resembling spreadable gels.
Heating under pressure gives smooth, homogenous
solutions at concentrations as high as 18-20%. Heating
Gum Karaya dispersions increases the solubility but
results in permanently lower viscosities. The pH of a
normal 1% dispersion is 4.6. Electrolytes such as
sodium, calcium and aluminium chlorides and aluminium
sulphate cause a viscosity drop as well as excessive
acid or alkali. Higher viscosities and pH stability over
a wider range can be obtained by hydrating the gum prior
to pH adjustment. At pHs above 7, the dispersion is
transformed into a ropy, stringy mucilage. In dry form,
Karaya loses viscosity in storage, especially under high
heat and humidity with the rate of loss being more for
powdered material as compared to granules. To minimise
this, storage under colder temperatures is advised. The
viscosity loss of Karaya dispersions in storage can be
minimised by the addition of preservatives like
benzoates, sorbates, phenols and related compounds.
Following are some of the applications of Gum Karaya :
Used in dental adhesive products.
Used as a bulk laxative
As an adhesive for ostomy rings
It is used as a stabilizer for dairy products and frozen
It is used as an acid resistant stabilizer for sherbets,
fruit ices and similar low pH products.
It is used in stabilizing packaged whipped cream
products, meringue toppings and aerated dairy foods.
is also used to prevent syneresis and improve the
spreadability characteristics of cheese spreads.
It is a good emulsion stabilizer for French style salad
It is used as a binder for making low calorie
dough-based products such as pasta, bread and other
It is very effective in preparation of special
quick-cooking farina cereals.
It is used in ground meat products as it provides good
water holding and binding properties to yield finished
In the paper industry, it is used in the manufacture of
long fibered, light weight papers.