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

Optical microscopy, ultracentrifugation, phase analysis and turbidimetric t itration methods were used to study phase state and phase equilibria of qua ternary water - gelatin-pectin-dextran system in the absence of salts and a t pH higher than the isoionic point. It was found that these systems are tw o-phase ones, contrary to the single-phase behaviour of the ternary water-g elatin-pectin and water-gelatin-dextran systems under the same conditions. The observed phase separation is the result of incompatibility of gelatin w ith pectin, dextran molecules being distributed practically uniformly betwe en coexisting phases. This phenomenon is rather typical for many water-gela tin-polysaccharide-1-polysaccharide-2 systems tinder the conditions when al l the pairs of biopolymers are compatible. The high compatibility of gelati n with pectin or dextran in the ternary systems under given conditions is d ue to the formation of weakly bonded interpolymer complexes. The incompatib ility of gelatin with pectin in the presence of dextran can be explained by the blockage of the reactive gelatin groups due to their competitive inter actions with dextran. (C) 2001 Elsevier Science BN. All rights reserved.