Microstructure and rheology design in protein–protein–polysaccharide composites

The microstructure and rheology of protein–protein–polysaccharide composites were explored, with wheat or soy protein used to modulate the microstructure and rheological properties of both gelatin and gelatin + starch gels. The extent of phase separation typically associated with protein–polysaccharide mixtures was greatly curtailed in the presence of either plant-based protein. The negatively-charged soy protein generally increased the elastic modulus of the gelatin + starch gels whereas the positively-charged wheat protein decreased it. Unique rheological behaviour was observed when both starch and 6 wt% plant-based protein were present, as the phase-separated gels became soft and flowable. Microstructurally, addition of soy protein to gelatin led to the presence of coacervates whereas the wheat protein aggregated within the continuous gelatin phase. In gelatin + soy + starch mixtures, the gelatin and soy remained mixed as the continuous phase and starch existed as the discontinuous phase. In gelatin + wheat + starch mixtures, a complex multiple phase-separated microstructure was evident as the three biopolymers appeared distinct. Overall, these results demonstrated that plant-based proteins may be used as structure modifiers to generate novel phase-separated gels with diverse rheological properties.