Rennet-induced aggregation of milk containing homogenized fat globules. Effect of interacting and non-interacting fat globules observed using diffusing wave spectroscopy

The dynamics of the interactions between casein micelles and oil droplets during rennet-induced gelation were described using rheology and diffusing wave spectroscopy. Two different colloidal states were obtained by preparing WPI-stabilized oil droplets in either milk serum or low ionic strength buffer: flocculated and non-flocculated. These two colloidal states strongly affected the diffusion of the non-interacting droplets in the gel and the elasticity of the protein network. In homogenized milk, the droplets interact with the protein network and play a structuring role, causing an increased elastic modulus. However, after displacement of the protein from the interface using Tween 20, the interpretation of the rheological data would lead to incorrect conclusions without light scattering measurements. This work demonstrated that an in-depth understanding of the colloidal properties of the oil droplets is necessary to fine-tune the interactions between these particles and the casein matrix in dairy gels.