Properties of amidated pectins. II. Polyelectrolyte behavior and calcium binding of amidated pectins and amidated pectic acids

The intrinsic pK values, as well as the free fractions of sodium and calcium counterions, were determined on salt‐free solutions of amidated pectinates and amidated pectates. The apparent pK values were non dependent of the degree of amidation but only to the effective charge density of the pectic polymers and an unique value of 2.9 ± 0.1 was found for the intrinsic pK value. The results obtained by conductimetry and with (sodium and calcium) specific electrodes showed a blockwise distribution of amide and acid groups in amidated pectates and a blockwise distribution of amide groups and a rather statistical distribution of acid groups in amidated pectinates.