Fine-stranded mixed gels of whey proteins and gelatin

Rheological properties of mixed and pure gels of gelatin and whey protein concentrate (WPC) have been investigated by means of tensile tests and dynamic oscillatory measurements. The microstructure of the system has been evaluated by transmission electron microscopy. The pH values chosen are within the range where the WPC forms a fine-stranded network structure, i. e. pH 7.5 and 3.0. When the ratio between the polymers was varied at pH 7.5, a shift in rheological properties was observed. The shift took place around 10% WPC addition to 3% gelatin. Below the shift, the mixed gels followed the behaviour of gelatin, and above, they followed the behaviour of WPC. Gel formation studies showed that the components gel individually, suggesting a phase-separation of the polymers. The gel formation of the WPC was independent of the presence of gelatin, while that of gelatin was shown to be dependent on the presence of WPC. At concentrations below the shift the mixed gels were remeltable and the system was interpreted as gelatin-continuous. At concentrations above the shift, the microstructure of the mixed gels suggested that a phase-separated, bicontinuous system was formed. The WPC network structure seemed to be unchanged in the presence of gelatin. No microstructural phase inversion took place. At pH 3.0 the gel formation of the WPC was strongly affected by the presence of gelatin, i.e. a stronger gel with an earlier gel point was formed. The microstructure of the system showed that an inhomogeneous, aggregated mixed gel, containing large pores, was formed.