STRUCTURE AND SOLUTION PROPERTIES OF TAMARIND-SEED POLYSACCHARIDE

The major polysaccharide in tamarind seed is a galactoxyloglucan for which the ratios galactose:xylose:glucose are 1:2.25:2.8. A minor polysaccharide (2-3%) contains branched (1 --> 5)-alpha-L-arabinofuranan and unbranched (1 --> 4)-beta-D-galactopyranan features. Small-angle X-ray scattering experiments gave values for the cross-sectional radius of the polymer in aqueous solution that were typical of single-stranded molecules. Marked stiffness of the chain (C infinity 110) was deduced from static light-scattering studies and is ascribed partially to the restriction of the motion of the (1 --> 4)-beta-D-glucan backbone by its extensive (approximately 80%) glycosylation. The rigidity of the polymer caused significant draining effects, which heavily influenced the hydrodynamic behaviour. The dependence of ''zero-shear'' viscosity on concentration was used to characterise ''dilute'' and ''semi-dilute'' concentration regimes. The marked dependence on concentration in the ''semi-dilute'' region was similar to that for other stiff neutral polysaccharide systems, ascribed to ''hyper-entanglements'', and it is suggested that these may have arisen through a tenuous alignment of stiffened chains.