Multiscale approach to characterize bulk, surface and foaming behavior of casein micelles as a function of alkalinisation

• Structural state of casein micelles significantly depends on pH value.
• Structural modifications were reflected in bulk, interfacial and foaming properties.
• Interfacial dilatational properties correlate with adsorption rate.
• Highest foam stability accompanied by maxima in interfacial dilatational properties.
• Maximum foam stability for most voluminous casein micelles.

Caseins display the major protein fraction in milk, and thus, significantly impact on milk's techno-functional properties such as foaming. As the micellar structure is mainly stabilized by hydrophobic as well as electrostatic forces, a gradual increase in pH value from 6.0 to 11.0 induced pronounced structural modifications. In consequence of alkalinisation, micelle size and composition changed. This had an impact on the solution properties such as turbidity. Furthermore, interfacial characteristics, e.g. surface pressure evolution and surface dilatational properties were affected. Different situations occurred regarding interfacial covering, which was also reflected in the resulting foam structures. The highest foam stability was obtained for pH 9.0. At this pH, highly voluminous casein micelles combined with a considerable amount of serum casein formed maximal viscoelastic surface layers. Micelle dissociation reduced viscoelasticity as well as foam stability, whilst drainage increased.

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