TEMPERATURE-COMPOSITION PHASE-DIAGRAM AND GEL PROPERTIES OF THE GELATIN-STARCH-WATER SYSTEM

The gelatin-starch-water system has been studied at different temperat ures, at a total biopolymer concentration of 5.0 wt%. The weight ratio s (W) of gelatin/starch used were 9:1, 8:2..... 2:8, 1:9, with pH valu es between 5.82 (at W = 9:1) and 6.50 (at W = 1:9). The systems were c haracterized theologically and by turbidity measurements to construct a phase diagram in the temperature (T) and composition (W) variables. The T-W quadrant consists of three regions: a single-phase solutions r egion (A) and regions of complete and incomplete phase separation (B a nd C, respectively). The system in region C is a gel. Region B, lying between A and C, corresponds to two co-existing liquid phases. The tra nsition from A to C (obtained by cooling the system at constant W) inv olves crossing region B. The properties of the resulting gels depend o n the rate of this intersection. Gels formed on rapid cooling have an even distribution of turbidity, whereas slow cooling gives two gel lay ers of different turbidity. The gelation temperature and gel strength of the mixed systems are dominated by the gelatin component, with no i ndication of network formation by starch. Copyright (C) 1996 Elsevier Science Ltd.