Effect of polymeric cosolutes on calcium pectinate gelation. Part 2. Dextrans and inulin

In a continuation of the work reported in the preceding paper, the effect of chicory root inulin (M_r≈4.5 kD) and branched dextrans of M_r 67, 464 and 2000 kD on gelation of low methoxy pectin (DE 31; 2.0 wt%; pH≈2.9–3.0) on cooling from 90 to 5 °C in the presence of stoichiometric Ca²⁺ has been characterised by low amplitude oscillatory measurements of G′ and G″. As found for other polymeric cosolutes studied previously (oxidised starch, potato maltodextrin, guar gum and locust bean gum), increasing concentrations of dextran or inulin caused a progressive increase of G′ and G″ in the solution state at 90 °C (attributed to segregative interactions promoting formation of calcium-mediated ‘egg-box’ junctions between pectin chains) and a progressive reduction in final moduli at 5 °C (attributed to excessive association of calcium pectinate into large aggregated bundles), with cooling curves crossing those for calcium pectinate alone at 55 °C. For the dextran samples, the ability to promote initial association of pectin chains at high temperature decreased with increasing molecular weight (i.e. with the smallest molecules having the greatest effect, as was also found for guar gum), but the reduction in final modulus on completion of cooling to 5 °C became more pronounced. By the criterion of the decrease in the change in log G′ during cooling, the three dextran samples studied seem roughly comparable in their overall effectiveness in promoting self-association of pectin, with inulin having a substantially smaller effect. Both materials, however, are less effective than the partially depolymerised starches and galactomannans studied previously. It is tentatively suggested that this may be associated with the flexibility introduced by the presence of three single bonds in the predominant glycosidic linkages of both dextran and inulin.