Kinetics of milk coagulation: I. The kinetics of kappa casein hydrolysis in the presence of enzyme deactivation

The kinetics of the primary phase of the enzymatic coagulation of milk, i.e., kappa-casein hydrolysis, was investigated in the presence and in the absence of concurrent enzyme deactivation processes. For conditions under which the enzyme is stable, the rate of hydrolysis can be described by Michaelis-Menten kinetics, as has been reported by previous investigators. A mathematical model, experimental data, and parameter estimates are provided for kappa-casein hydrolysis in the presence of concurrent deactivation of enzyme. The model accurately describes the experimental results when porcine pepsin was used as the renneting enzyme. The model and the experimental results indicate that samples of milk treated under conditions where deactivation of enzyme is significant can have fractional conversions of kappa-casein ranging from zero to unity and yet contain no active enzyme at the termination of the treatment.