USANS and SANS investigations on the coagulation of commercial bovine milk: Microstructures induced by calf and fungal rennet.

Coagulation of milk is a fundamental process in the manufacture of dairy products. Under the enzymatic action of rennet, casein micelles form aggregates resulting in a fractal gel network. There are few studies of microstructures using scattering techniques resulting from rennet coagulation in commercial milk in its native state. Here we employ ultra-small angle neutron scattering (USANS) and small angle neutron scattering (SANS) covering the scattering q -vector range of 5 × 10 - 5 < q < 2 × 10 - 2 Å - 1 and the fractal cylinder model to study fractal structures and sizes resulting from calf and fungal rennet-induced coagulation of commercial skim and whole milk. We report evidence of aggregation with fractal properties analogous to that of swollen, randomly-branched polymers. Calf rennet resulted in a larger fractal dimension in skim compared to whole milk. In milk coagulated by fungal M. miehei , the randomly-branched polymer-like structures had a slightly larger fractal dimension of 2.5 and the structural unit was smaller. These measurements provide an important foundation for continuing study of the structure of commercial cheese with scattering techniques. Image 1 • Commercial milk coagulation with ultra-small and small angle neutron scattering. • Microstructure modelled by fractal cylinders predicted by simulation. • Fat globules have little effect on the gel fractal dimensions. • With fungal rennet, fractal dimension increases, object size decreases. • Time-dependent behaviour of fractal microstructure growth. [ABSTRACT FROM AUTHOR]