The influence of casein on the kinetics of hydroxyapatite precipitation

Abstract

The influence of whole casein as well as the isolated α sI-, β-, and κ-casein on the precipitation of HAP at pH 6.7 and T = 37°C is reported. Already at low concentrations (10 −8-10 −7 M), where effects of complex formation on the supersaturation can be neglected, a strong retardation of HAP formation is noted. The inhibition appears to be caused by effects in the early stages of the reaction, whereas the fast apatitic growth is hardly affected. The inhibitory action increases in the order κ < β < α sI corresponding with the amount of SerP groups. A simple Langmuir adsorption model can explain the growth retardation. At high casein concentration the main precipitating phase is OCP, growing at the expense of HAP. This effect is also shown with α sI- and β-casein whereas κ-casein does not include changes in the precipitating phases.