The effect of depolymerised guar gum on the stability of skim milk

We studied the interactions between casein micelles and (depolymerised) gua r gum, degraded by heating its aqueous solutions at low pH. The guar sample s were characterised by a combination of size-exclusion chromatography and light scattering, which yielded the distribution of molar mass and correspo nding radius of gyration. The relation between molar mass and radius of gyr ation showed that guar can be described as a random coil. Mixing guar gum w ith casein micelles led to a phase separation. This phase separation origin ates from a depletion interaction leading to an effective attraction betwee n the casein micelles by non-adsorbing guar. The polymer concentration at t he phase boundary increases with decreasing guar chain length. Vrij's theor y for depletion interaction was used to calculate the phase boundary from t he size of the casein micelles and the size and molar mass of the guar samp les. The theory of Vrij predicts the trends for the phase boundary with res pect to the molar mass dependence as found experimentally. (C) 2000 Elsevie r Science Ltd. All rights reserved.