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Gum Karaya 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 hot season. 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.
Then the gum is sold to Gum Karaya associate shippers like Krystal Colloids 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 follows: -
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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. APPLICATIONS:
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