ISHS Acta Horticulturae 108: International Cashew Symposium
THE STRUCTURE OF THE GUM OF ANACARDIUM OCCIDENTALE |
| Authors: | S. BOSE, M. BISWAS |
| Abstract:
The gum from the cashewnut tree occurs in the form of pale yellow to reddish stalactic masses. In cold water it swells up into a jelly like mass but dissolves rapidly when heated. Due to its insecticidal and good adhesive properties, the gum finds extensive application in book binding. An electrophoretically pure acidic polysaccharide, [ œ ] D22 + 18.03°, M.W. 6.412 x 104, has been isolated from this gum. Its structure has been elucidated from immunochemical reactions, hydrolysis under different conditions, methylation, and periodate oxidation studies. Complete acid hydrolysis shows that cashew gum is built up of D-galactose, L-arabinose, D - galacturonic acid and L-rhamnose (in traces). Cross reactions with different anti-sera confirm the presence of non-reducing galactose units reinforced in some cases with L-rhamnose residues in the gum. Autohydrolysis of the gum generates a degraded gum, M.W. 23250, which upon graded hydrolysis furnishes an aldobiouronic acid the structure of which has been established as 6–0- (  - D - galactopyranosyl uronic acid) - D - galactose.
Finally, the structures of degraded and natural cashew gums have been settled from the result of methylation, periodate oxidation followed by Smith degradation experiments.
Degraded cashew gum is a branched chain polysaccharide and its repeating unit consists of a 1 * 3 linked galactan main chain to which are attached galactose residues by 6 * 1 linkages as side chains.
Every alternate galactose residue constituting the branch carries aldobiouronic acid moieties also joined by 6 * 1 linkage.
The natural cashew gum differs from the degraded gum with respect to the size of the main galactan chain and in the number of auxilliary chains.
In addition, the natural gum carries a side chain L-Araf (1 * 3) L-Arap (1….attached to a galactose moiety of one of the auxilliary chains). The D.P. values of the degraded and natural cashew gum, as calculated from the molecular weights, were found to be 17 and 13, respectively.
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