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.