ION COMPLEXATION OF BIOPOLYMERS - MACROMOLECULAR STRUCTURE AND VISCOELASTIC PROPERTIES OF GELS

The effect of charge density and solvent conditions have been explored on sodium pectinate - calcium system undergoing gelation. Viscosity and shear modulus were determined respectively before and after the transition. More than 55% of sugar residues need to be charged to build a network. The amount of calcium required increases dramatically with the decrease of pH and ionic strength. Pectins in salt - free solutions are rapidly connected by calcium ions but the crosslink density remains lower than in NaCl-rich solutions. Small angle X-ray scattering indicates that the junction zones may be viewed as rod-like cylinders whose cross - section radius increases from 3 to 6 and 8 angstrom when the ratio R = 2 (Ca2+)/(COO-) changes from 0 to 0.5 and 0.75.