Shear modulus-concentration relationships for low DE pectin-calcium gels In the temperature range 20-85 degrees C

Gelation of solutions of a DE 35% sodium pectinate (pH 7.4 in 0.2 mol/dm(3) NaCl) by addition of calcium chloride (fixed stoichiometric ratio R = 0.4) was followed by oscillatory mechanical spectroscopy. Shear modulus values (G') attained after an appropriately long cure time (and at a particular temperature) were analysed as a function of concentration using a previously described computer approach based on cascade theory. Modulus-concentration data obtained by taking 'slices' through gel 'meltdown' curves, generated from 20 degrees C gels by steady heating, were also treated in this way. Parameters from the cascade theory, when expressed in terms of temperature, led to estimates for the cross-linking enthalpy and entropy, and to the suggestion that 'a', the non-ideal front factor, though close to unity, was a function of the ratio of concentration to critical concentration, i.e. C/C-o.