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.

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 Society.


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 follows :
 




GRADE/SPEC. COLOUR BFOM VISCOSITY AT 1 %
HPS White 0.5 % max >1200 cps
No.1 White with slight gray cast 0.75% max >1000 cps
No.2 Light tan 2% max >800 cps
No.3 Tan 3% max >700 cps


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: 

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 desserts.

  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.

  It is also used to prevent syneresis and improve the spreadability characteristics of cheese spreads.

  It is a good emulsion stabilizer for French style salad dressings.

  It is used as a binder for making low calorie dough-based products such as pasta, bread and other bakery products.

  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 products.

  In the paper industry, it is used in the manufacture of long fibered, light weight papers.
 

 

 

 

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