Effect of processing conditions on the foaming behavior of casein micelle dispersions

Summary

Various studies indicated that the foaming properties of milk are strongly influenced by the composition of the milk as well as the conditions applied during processing [1]. However, the role of surface and bulk components in complex food systems like milk on foam formation and stability is still not well understood. For example, it often happens that a certain batch of milk does not
foam properly while others do, even if they are processed in the same way. It is still unclear what causes this and how it can be solved. Previous studies indicated that casein micelles play an important role in the stability of milk foams. Therefore, we studied, at 20°C, the foaming behavior, interfacial, and thin film properties of casein micelle dispersions (CMD) that were initially prepared
at different temperatures (4 and 20°C). CMD prepared at 4°C, with more agregates of casein micelles and β-casein in the serum, resulted in much more stable foams than CMD prepared at 20°C. We investigated the linear and nonlinear surface rheology of air/water interface stabilized by CMD at different frequency and strain. Large deformation surface rheology analyzed by Lissajous
plots showed significant strain hardening in compression and a yielding behavior of the interfacial structure when the interface is expanded. The frequency dependence of the dilatational modulus is significantly different between CMD’s prepared at 4 and 20°C, and at low frequencies the modulus of the CMD prepared at 4°C is about two times higher than the modulus of the CMD
prepared at 20°C. This correlates well with the observed higher stability of the according foams.
Atomic force microscopy was conducted to study the structure of the air/water interface of CMD. Thin film structure and stability were also investigated. By analyzing correlations between the findings obtained with these experiments and foaming behavior, we assessed the role of processing conditions on the stability of CMD foams.