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

Abstract

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<2×10-2Å-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.