SOLUTION PROPERTIES OF PECTIN POLYSACCHARIDES .2. CONFORMATION AND MOLECULAR-SIZE OF HIGH GALACTURONIC ACID CONTENT ISOLATED PECTIN CHAINS

The solution properties of flax pectins and commercial pectins with high galacturonic acid content (AGA > 80%) were studied by low-angle laser-light scattering (LALLS), viscosity and Size Exclusion Chromatography (SEC) experiments performed in 0.2 M aq. NaCl. LALLS data were strongly affected by the presence of a small amount of high molecular weight superstructures. Molecularly dispersed pectin solutions could be obtained after complete removal of these high molecular weight particles by various procedures. The conformation of isolated pectin chains has been determined from the relationship between molecular weight, M(w), [eta] and the distribution coefficient (K(d)) measured on the Sephacryl 200/0.2 M NaCl chromatographic system. Analysis of the results, combined with a set of literature data, in terms of the known theories for rods and worm-like chains, gave values of 67 angstrom and 6 angstrom for the persistence length and the hydrodynamic diameter, respectively, of pectin in 0.2 M NaCl. These results suggest that pectin with a high galacturonate content behaves in NaCl solution like an extended coil with a similar conformation to the alginate chain.