MIXED GELS OF GELATIN AND WHEY PROTEINS, FORMED BY COMBINING TEMPERATURE AND HIGH-PRESSURE

Mixed and pure gels of gelatin and whey protein concentrate (WPC) were formed by using temperature and high pressure simultaneously Combinin g these gel formation methods enables the two polymer networks to set at the same time. The microstructure of the gels was studied by means of light microscopy and transmission electron microscopy, and the rheo logical properties by means of dynamic oscillatory measurements and te nsile tests. The pH values investigated were 5.4, 6.8 and 7.5. The iso electric point of the WPC is around pH 5.2 and that of gelatin between pH 7.5 and 9. At pH 5.4, the mixed gel formed a phase-separated syste m, with a gelatin continuous network and spherical inclusions of the W PC. The storage modulus (G) of the mixed gel was similar to that of a pure gelatin gel. At pH 6.8, the mixed gel formed a phase-separated sy stem, composed of an aggregated network and a phase with fine strands. The aggregated network proved to be made up of both gelatin and WPC, and the fine strands were formed of gelatin. The mixed gel at pH 6.8 s howed a high G compared with the pure gels, which decreased significan tly when the gelatin phase melted. At PH 7.5 the mixed gel was compose d of one single aggregated network, in which gelatin and WPC were homo geneously distributed. rt was impossible to distinguish the gelatin fr om the WPC in the mixed network. The mixed gel at pH 7.5 showed a sign ificantly higher G than the pure gels As the gelatin phase was melted out for the mixed gel, a large decrease in G was observed. The pure ge latin gels, formed by a temperature decrease under high pressure, prov ed to be pH-dependent, showing an increase in aggregation as the pH in creased from 5.4 to 7.5. A fine-stranded, transparent gelatin gel was formed at PH 5.4, while an aggregated, opaque gel was formed at pH 7.5 . The stress at fracture for the gelatin gels decreased as the aggrega tion, and consequently the pore size, increased.