Kinetic evidence for steric destabilization of casein by rennet enzyme activity

Abstract

The kinetics of the aggregation step of milk enzymic coagulation have been studied, working at high enzyme/substrate concentration ratios, in order to separate this step from the proteolysis. The initial rate of aggregation of the proteolysed casein micelles (CM) was estimated from the initial rate of turbidity increase (∂/∂t)₀, at different casein concentrations, temperatures and viscosities of the medium, applying the Rayleigh–Debye–Gans scattering theory. The results obtained showed an initial second-order kinetics for the process, as proposed by Smoluchowski's hypothesis of initial doublet formation for Brownian flocculation. The value obtained for the stability factor pointed to the presence of an important steric stabilization, even after almost total cleavage of the stabilizing k-casein external layer. Variations of temperature and viscosity of the medium indicated that the stability of pCM is directly related to surface structural characteristics.