Co-gelation of calcium pectinate with potato maltodextrin. Part 1. Network formation on cooling

Small deformation oscillatory measurements of storage and loss moduli (Gʹ and Gʹʹ) have been used to explore the effect of segregative interactions in gelling mixtures of calcium pectinate (DE 31.1; stoichiometric Ca2+) and potato maltodextrin. Solutions were prepared at 90°C and gelled by cooling to 5°C at a rate of 1°C/min. Two different methods of sample preparation were used, which gave very different rheology at high temperature, but had little effect on the networks formed on cooling. In most of the experiments, the pectin concentration was held constant at 2.0 wt% and the concentration of maltodextrin was varied between 0 and 25 wt%. The moduli at 30°C, before the onset of gelation of maltodextrin, decreased steeply with increasing maltodextrin concentration, consistent with a collapse of the calcium pectinate network structure by formation of large aggregates in response to segregative interactions between the two polymers. At high concentrations of maltodextrin, network collapse could be seen directly as sharp drops in modulus during cooling. The final moduli at 5° C showed a similar reduction at maltodextrin concentrations up to ~12.5 wt%, but increased steeply at higher concentrations, due to gelation of maltodextrin. In a converse series of experiments, where maltodextrin concentration was held fixed at 20 wt% and the concentration of calcium pectinate was varied between 0 and 3.0 wt%, the observed moduli of the calcium pectinate networks immediately before gelation of the maltodextrin component were virtually independent of pectin concentration, consistent with the concept of a solubility product for unaggregated pectin chains proposed in the preceding study of gelation of calcium pectinate in the presence of oxidised starch. These qualitative interpretations are consolidated by quantitative analyses reported in the following paper.