PHASE-EQUILIBRIA AND GELATION IN GELATIN MALTODEXTRIN SYSTEMS .3. PHASE-SEPARATION IN MIXED GELS

Co-gels of potato maltodextrin Paselli SA-6 with gelatin were prepared by rapid quenching of mixed solutions from 90-degrees-C. At fixed set ting temperature and fixed concentration of gelatin, the time required to form a self-supporting network showed an initial steady decrease w ith increasing concentration of SA-6 (as expected from polymer exclusi on), but then increased dramatically before again decreasing. The inte rpretation of this behaviour as phase inversion from a gelatin-continu ous network with SA-6 inclusions to a (more slowly-forming) SA-6 netwo rk with gelatin inclusions was confirmed by differential scanning calo rimetry (showing both components melting separately, with no evidence of specific interaction), mechanical spectroscopy (showing that the mi xed gel network was destroyed completely by melting of the gelatin com ponent at low concentrations of SA-6, but only weakened at SA-6 concen trations above the inversion point) and by fight microscopy (showing t he expected changes in distribution of the two polymers). In similar s tudies using the faster-gelling potato maltodextrin Paselli SA-2, micr oscopy and gel-melting profiles again showed phase-inversion from a ge latin-continuous network at low concentrations of SA-2 to a maltodextr in-continuous network at higher concentrations. Inversion, however, oc curred at a lower concentration of maltodextrin than in the gelatin/SA -6 systems, and the accompanying change in gelation rate was confined to a sharp decrease in the dependence of gel-time on SA-2 concentratio n.