Interfacial properties, thin film stability and foam stability of casein micelle dispersions.

Foam stability of casein micelle dispersions (CMDs) strongly depends on aggregate size. To elucidate the underlying mechanism, the role of interfacial and thin film properties was investigated. CMDs were prepared at 4°C and 20°C, designated as CMD and CMD. At equal protein concentrations, foam stability of CMD (with casein micelle aggregates) was markedly higher than CMD (without aggregates). Although the elastic modulus of CMD was twice as that of CMD at 0.005Hz, the protein adsorbed amount was slightly higher for CMD than for CMD, which indicated a slight difference in interfacial composition of the air/water interface. Non-linear surface dilatational rheology showed minor differences between mechanical properties of air/water interfaces stabilized by two CMDs. These differences in interfacial properties could not explain the large difference in foam stability between two CMDs. Thin film analysis showed that films made with CMD drained to a more homogeneous film compared to films stabilized by CMD. Large casein micelle aggregates trapped in the thin film of CMD made the film more heterogeneous. The rupture time of thin films was significantly longer for CMD (>1h) than for CMD (<600s) at equal protein concentration. After homogenization, which broke down the aggregates, the thin films of CMD became much more homogeneous, and both the rupture time of thin films and foam stability decreased significantly. In conclusion, the increased stability of foam prepared with CMD appears to be the result of entrapment of casein micelle aggregates in the liquid films of the foam.