Functional properties of bovine milk protein isolate and associated enzymatic hydrolysates

The nitrogen solubility (pH 2.0-8.0), heat stability (pH 6.2-7.4) and viscosity (pH 6.2-7.4) properties of bovine milk protein isolate (MPI) and its Flavourzyme™, Neutrase™ and Protamex™ enzymatic hydrolysates were studied. Gel permeation chromatography indicated digestion of individual milk proteins in all hydrolysates. MPI had low solubility at pH 4.0-5.0; however, hydrolysis with all enzymes significantly increased solubility between pH 4.0-7.0. MPI was highly heat stable at 140 °C above pH 6.8 (>10 min). All hydrolysates coagulated within 64 s at 140 °C between pH 6.2-7.4. All hydrolysates displayed increased apparent viscosities upon exposure to simulated high temperature short time (HTST) heating and cooling conditions between pH 6.2-7.4. The results demonstrate that enzymatic hydrolysis of MPI increased protein solubility; however, the heat stability was reduced. The apparent viscosity was lower than the control at ambient temperature and increased at 90 °C.