Gum karaya is the dried exudates 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 best quality gum is collected during Arpil, may and june i.e in summer .During this time as the weather 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 solution than the gum collected in summer. The local tap the tree by making incisions upto one square foot in dimension on the trunk.The gum begans to excude immediately and the excudation continous for several days. The maximum amount of excudation occours with in the first 24hrs. The gum is in the form of huge irregular tears.The tears are picked by locals who sell the same to the Registered Forest Contractors.Then the gum is sold to the Gum karaya Associates like Adinath Gum Industries. who process the lots after basic tests. Bark and other contaminants are first removed, the tears are then broken up and the fragments are sorted into grades on the basic of colours.
Karaya is a calcium and magnesium salt, with a central chain of D- galactose, L- rhamnose, D- galacturonic acid units, with sum side chains containing D- glucuronic acid.Although designated as a water soluble gum , Karaya is one of the least soluble. A gum particle placed in water doesnot dissolvebut absorbs waters and swells many times its original size.The particle size influence the type of the dispertion obtainable. A coarse granulated karaya yield a discontinuous,grainy dispersion, a finely powdered gum yield an apparently homogenous dispersion. In dilute solution of Gum Karaya , the viscosity increases linearly with concentration upto about 0.5 %, thereafter karaya dispersions behave as non-Newtonian solution. At concentration above 2-3 % gum karaya forms thick, non flowing pastes resembling speedable gel. Heating under pressure give smooth, homogenous solution at concentration as high as 18-20 % . Heating gum karaya dispersions increases the solubility, but results in permanently lower viscosities. In dry forms, karaya loses viscosity in storage, especially under high heat & humidity with the rate of loss being more for powdered material as compare to granules. The viscosity lost of karaya dispersion in storage can be minimized by addition of preservative like benzoates, sorbates, phenols & related compounds.
APPLICATIONS OF GUM KARAYA
1.Used in dental adhesive products.
2.It is used as a stabilizer for dairy products & frozen desserts.
3.It is used as binder for making low calorie dough-based product as pasta, bread & other bakery products.
4.It is used ion ground meat products as it provides good water holding & binding property to yield finished products.
5.In the paper industry it is used in manufacture of long fibred, light weight papers.
6.It is used in textile printing operations as a thickening agent for the dye in direct colour printing on cotton fabrics.