The effect of the degree of esterification on the hydrodynamic properties of citrus pectin

Estimation of the influence of the degree of esterification on the hydrodynamic properties of citrus pectins provides a simple demonstration of how chemical variation can influence structural properties of polysaccharides. Five citrus pectins with average degree of esterification 77.8, 65.0, 53.9, 37.8 and 27.9%, respectively were studied using capillary viscometry, sedimentation velocity, sedimentation equilibrium and size exclusion chromatography coupled to multi-angle laser light scattering (SEC-MALLS). Molecular weights (weight average) for all five pectin samples were within the range 190 000 ± 30 000 g/mol as confirmed by the independent techniques of sedimentation equilibrium and SEC-MALLS. Estimates for the conformation dependent Wales-van Holde (k(s)/[η]) and frictional (f/f0) ratios from the hydrodynamic data clearly indicates increasing chain stiffness with decreasing degree of esterification. It appears that both steric and electrostatic interactions are important in these conformational changes. (C) 2000 Elsevier Science Ltd.