Page 15 - Physicochemical properties of Indian plant gums- IINRG, Ranchi

Karaya gum (Sferculia urens)

General Information

Karaya gum also known as Indian tragacanth. is the dried exudate from the tree
urens. It is also known as Katira gum or Kullu gum in the trade. The tree Sterculia urms
is common in India in the tropical deciduous forests mostly in dry and rocky areas. Major
areas producing gum karaya are M.P., Andhra Pradesh, Maharashha, Orissa, Rajasthan,
Tamil Nadu and Mysore. The best quality gum is collected during April-June j.e. before
commencement of monsoon. As the weather becomes warrnet the gum leld and quality
improves. Collection may be repeated after the monsoons in September, although this gum
may be darker in color and lower in viscosity. When trees are incised or blazed, gum begins
to flow immediately, and exudation continues for several days. The maximum amount of
exudation occurs within the first 24hr. The yield ofthe gum from matured trees is estimated
at 1 to 4.5 kg per tree per season. The average tree can be tapped five times during the
lifetime.

In the natural state, the gum is in inegularly shaped pieces, sometimes of worm like
appearance. They are white or pinkish-brown il colour and generally striated. The gum,
especially when fresh, may have an acetous odour.
Physico-chemical properties

Chemical nature: Itispartiallyacetylatedcomplexpolysaccharide.Itcontainsapproximately

80% acetyl groups and around 37olo uronic acid residues with acid number varying from 17.4
to 22.7. Partial acid hydrolysis gives D-galactose, L-rhamnose (6-deoxy-L-mannose) and
Dgalacturonic acid along with the aldobiouronic acids [2-O-(a-D-galactopyranosyluronic
acid)-L-rhamnose, and 4-O-(o-D-galactopyranosyluronic acid)-D-galactosel and acidic
risaccharide [O-(a-D-glucopyranosyluronic acid)-(1--+3)-(p-D-galactopyranosyluronic
acid)-( I ---+2)-L-rhamnose]. The proportions ofvarious components ate 430lo D-galactouronic
acid,l3%oD-galactose and 15% L-rhamnose. Methylation and hydrolysis studies show that
D-galacturonic acid and L-rhamnose units are branch points in polysaccharide structure.
The molecular structure is still incompletely known.

Molecular weight: The molecular weight ofkaraya gum is 9,500,000. It was determined by
rhe Svedberg ultracenhifuge method and calculated by Svedberg's formula for which the
determination of sedimentation constants. (s), diffirsion constants (D), and partial specific
volumes (V) were made.
Swelling behaviour & Viscosity: It forms viscous mucilage at low concentrations and the
swelling behaviour is caused by the presence of acetyl groups. Chemical deacetylation
6mugh an alkali treatment results in a water-soluble gum. Dilute solution properties of
taraya gum were studied using size-exclusion chromatography, static and dynamic light
scattering and viscosity experiments. The native acetylated karaya gum assumes a rather