Gelation of pectinic acids in the presence of calcium counterions

Pectins are polysaccharides which are able to gel in the presence of calcium ions if their degree of esterification is lower than 40%. From a purified pectin, a de‐esterification was carried out by alkali and by enzymes in order to obtain samples with a different charge density and esterification pattern (random or blockwise distribution of carboxylic acid sites). The pectin‐calcium interactions were studied in a dilute solution of calcium pectinates by conductimetry. If the concentration of highly charged polymer is increased, a multichain association can occur: the same process is observed with dilute solutions (cp≤10‐3 eq. 1−1) but in the presence of an excess of calcium ions. This first step of the gelation was followed by light scattering and by viscometry. The gelling system can be described by a power law including a critical ratio (equivalent concentration of calcium ions/pectin carboxylic sites) and quasi‐critical exponents. The values of these critical parameters have been discussed as a function of charge density of the pectins, their esterification pattern, their concentration, and the nature of the divalent counterion.