PHASE-BEHAVIOR AND RHEOLOGY OF MIXED POLYMER SYSTEMS CONTAINING STARCH

Studies have been undertaken to monitor the phase behaviour of potato maltodextrin (PMD) in admixture with locust bean gum, gum arabic and carboxymethyl cellulose. Two phase liquid separation occurred at low total polymer concentrations for PMD/locust bean gum mixtures and the threshold concentration in water was similar to 3.5 and 2.8 wt% in 0.1 mol/dm(3) NaCl. Very much higher concentrations were required for the PMD/gum arabic system (threshold concentration in water >47 and 16 wt% in 0.1 mol/dm(3) NaCl. Carboxymethyl cellulose only induced phase separation if electrolyte was added and the threshold concentration was 10.8 wt%. The rheological properties of PMD were greatly influenced by the addition of gum arabic. At low additions, the storage modulus (G') was greatly enhanced, while at higher additions, corresponding to compositions in the two phase region of the phase diagram, lower values of G' were obtained. The rate of PMD gelation followed first order kinetics and the rate constant increased with increasing gum arabic concentration.