Co-gelation of calcium pectinate with potato maltodextrin. Part 2. Analysis of co-gel moduli

The experimental moduli reported in the preceding paper for co-gels of calcium pectinate (DE 31.1; stoichiometric Ca2+) with potato maltodextrin have been analysed using the procedures and assumptions developed for mixtures of calcium pectinate with oxidised starch. In outline, part of the calcium pectinate was assumed to be "precipitated" into a dispersed phase in response to segregative interactions between the two polymers, with the residual concentration of unprecipitated ("free") pectin being controlled by a solubility product K, defined as the maltodextrin concentration multiplied by the square of the concentration of free pectin, and with the phase volume of dispersed particles being directly proportional to the amount precipitated (constant of proportionality, k). The modulus of the continuous matrix was estimated by simple addition of the individual contributions from maltodextrin and free pectin, derived from standard calibration curves, and calculated values of co-gel moduli were obtained using the Takayanagi isostress blending law in the limiting form for an infinitely hard filler. Best-fitting values of K=2.8 and k=0.059 were identified by least-squares minimisation of the overall difference between observed and calculated values of log Gʹ at 5°C for mixtures incorporating 2.0 wt% calcium pectinate prepared by two different procedures and measured 100 and 400 min after the start of cooling from 90°C at 1°C/min, with maltodextrin concentrations in the range 0¯25 wt% (100 min values) or 0¯17.5 wt% (400 min), and for 20 wt% maltodextrin with 0¯3.0 wt% calcium pectinate (100 min values for one method of preparation). The fits to all five data sets were virtually within experimental error. The best-fitting value of k is almost identical to the value obtained for mixtures of calcium pectinate with oxidised starch (0.059 in comparison with 0.061), consistent with collapse of calcium pectinate network structure to a fixed concentration of ~17 wt% in both systems.