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 calc ium pectinate (DE 31.1; stoichiometric Ca2+) with potato maltodextrin have been analysed using the procedures and assumptions developed for mixtures o f calcium pectinate with oxidised starch. In outline, part of the calcium p ectinate was assumed to be "precipitated" into a dispersed phase in respons e to segregative interactions between the two polymers, with the residual c oncentration of unprecipitated ("free") pectin being controlled by a solubi lity product K, defined as the maltodextrin concentration multiplied by the square of the concentration of free pectin, and with the phase volume of d ispersed particles being directly proportional to the amount precipitated ( constant of proportionality, k). The modulus of the continuous matrix was e stimated by simple addition of the individual contributions from maltodextr in and free pectin, derived from standard calibration curves, and calculate d values of co-gel moduli were obtained using the Takayanagi isostress blen ding law in the limiting form for an infinitely hard filler. Best fitting v alues of K = 2.8 and k = 0.059 were identified by least-squares minimisatio n of the overall difference between observed and calculated values of log G ' at 5 degrees C for mixtures incorporating 2.0 wt% calcium pectinate prepa red by two different procedures and measured 100 and 400 min after the star t of cooling from 90 degrees C at 1 degrees C/min, with maltodextrin concen trations in the range 0-25 wt% (100 min values) or 0-17.5 wt% (400 min), an d 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 virtual ly within experimental error. The best-fitting value of k is almost identic al to the value obtained for mixtures of calcium pectinate with oxidised st arch (0.059 in comparison with 0.061), consistent with collapse of calcium pectinate network structure to a fixed concentration of similar to 17 wt% i n both systems. (C) 2000 Elsevier Science Ltd. All rights reserved.