An example of ionic complexation in biopolymers: The pectin‐calcium system

摘要: The calcium‐induced gelation of low methoxyl pectin has been studied by small‐angle X‐ray and neutron scattering and mechanical spectroscopy. Whilst neutron scattering indicates little polymer conformational change as calcium becomes bounded, the X‐ray data are consistent with junction zones viewed as rod like cylinders whose cross section radius increases from 0.3 to 0.8 nm with the amount of calcium added. Near the sol‐gel transition the results of oscillatory shear measurements agree very well with the prediction of the percolation model. On fully set gels, the mechanical spectrum allow to point out that cross‐links in these gels may be considered as permanent. The magnitude of the equilibrium shear modulus obtained from these dynamic mechanical analysis increases with calcium and pectin concentration and with the ionic strength. Generally solvent expulsion occurs when the above three …