Phase state of aqueous gelatin-polysaccharide (1)-polysaccharide (2) systems.

Optical microscopy, ultracentrifugation, phase analysis and turbidimetric titration methods were used to study phase state and phase equilibria of quaternary water-gelatin-pectin-dextran system in the absence of salts and at pH higher than the isoionic point. It was found that these systems are two-phase ones, contrary to the single-phase behaviour of the ternary water-gelatin-pectin and water-gelatin-dextran systems under the same conditions. The observed phase separation is the result of incompatibility of gelatin with pectin, dextran molecules being distributed practically uniformly between coexisting phases. This phenomenon is rather typical for many water-gelatin-polysaccharide-1-polysaccharide-2 systems under the conditions when all the pairs of biopolymers are compatible. The high compatibility of gelatin with pectin or dextran in the ternary systems under given conditions is due to the formation of weakly bonded interpolymer complexes. The incompatibility of gelatin with pectin in the presence of dextran can be explained by the blockage of the reactive gelatin groups due to their competitive interactions with dextran.