Effects of globular protein type and concentration on the physical properties and flow behaviors of oil-in-water emulsions stabilized by micellar casein–globular protein mixtures

• At high protein-to-oil ratio, the globular protein type and concentration have little effect on the size of droplet formation.
• The mixture of micellar casein isolate and whey protein concentrate causes droplet flocculation.
• The globular protein type and concentration determine the functional properties of mixed protein emulsion.
• Increased of globular protein content in protein mixture containing caseins reduces the heat stability.
• The initial heating pH have an impact on the creaming stability and shear flow behavior.

The influence of different globular protein sources (soy, pea and whey proteins), casein-to-globular protein ratios (6:4 and 4:6), and initial heating pH values (6.6, 6.9 and 7.2) on the heat stability, creaming stability, and flow behavior of mixed protein stabilized emulsions (10% w/w protein and 10% w/w oil) was studied. Fine emulsions in the nanometric range (<300 nm) were formed and the emulsification was not significantly affected by the globular protein sources and mixed micellar casein–globular protein ratios. Flocculation was observed after homogenization when whey proteins were present in the micellar casein–globular protein mixtures, which may have been caused by a bridging-type droplet flocculation with a mean particle size of up to 10 μm. Furthermore, the higher the whey protein content, the more extensive the droplet flocculation. Heat treatment at 90 °C for 15 min generally decreased the heat stability and resulted in more shear-thinning behaviors of the mixed protein-stabilized emulsions. Those changes were mainly attributed to the denaturation and aggregation of globular proteins. Of the three globular proteins, the soy proteins gave the highest heat stability in combination with micellar caseins. This work also showed that the extent of heat-induced destabilization was dependent on the pH value during initial heating, denaturation temperature, concentration and inherent mineral contents of the globular proteins. Particle size distribution, microstructure and rheological measurements showed strong correlations with heat stability.

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