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 degrees C and 20 degrees C, designated as CMD4 degrees C and CMD20 degrees C. At equal protein concentrations, foam stability of CMD4 degrees C (with casein micelle aggregates) was markedly higher than CMD20 degrees C (without aggregates). Although the elastic modulus of CMD4 degrees C was twice as that of CMD20 degrees C at 0.005 Hz, the protein adsorbed amount was slightly higher for CMD20 degrees C than for CMD4 degrees C, 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 CMD20 degrees C drained to a more homogeneous film compared to films stabilized by CMD4 degrees C. Large casein micelle aggregates trapped in the thin film of CMD4 degrees C made the film more heterogeneous. The rupture time of thin films was significantly longer for CMD4 degrees C (>1 h) than for CMD20 degrees C (<600s) at equal protein concentration. After homogenization, which broke down the aggregates, the thin films of CMD4 degrees C 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 CMD4 degrees C appears to be the result of entrapment of casein micelle aggregates in the liquid films of the foam. (C) 2016 Elsevier B.V. All rights reserved.