PHASE-EQUILIBRIA AND GELATION IN GELATIN MALTODEXTRIN SYSTEMS .2. POLYMER INCOMPATIBILITY IN SOLUTION

The effect of thermodynamic incompatibility in mixed solutions of gelatin and Paselli maltodextrins SA-6 and SA-2 has been studied at a temperature (45-degrees-C) where the individual polymers are stable as disordered coils. Concentrated mixtures of SA-6 and gelatin showed classic phase separation into two co-existing liquid layers, with compositions lying along a well-defined binodal. On decreasing SA-6 concentration below the binodal, however, a substantial proportion (up to 60%) of the maltodextrin was precipitated, with normal single-phase solutions occurring only at much lower concentrations of both polymers. SA-2 showed a more extreme version of the same behaviour, with precipitation of up to 100% of the maltodextrin and no evidence of co-existing liquid phases at any accessible concentrations. In both cases, the amount of maltodextrin precipitated was proportional to the square of its initial concentration and to the first power of gelatin concentration, indicating that gelatin drives self-association and aggregation of maltodextrin when both polymers are present in a single liquid phase. H-1 NMR showed the precipitated maltodextrin to be higher in molecular weight and in degree of branching than the material remaining in solution, and particle-size analysis indicated that the volume of the individual maltodextrin particles increased linearly with the total mass precipitated.