The effect of milk and kappa casein on streptococcal glucosyltransferase.

Many dietary components such as carbohydrates, lipids and proteins may be incorporated into the salivary pellicle and thus may affect glucosyltransferase (GTF) activity on pellicle surfaces. The effect of milk on streptococcal GTF activity was determined. Milk, when coated onto buffer-coated hydroxyapatite or saliva-coated hydroxyapatite (sHA), reduced the subsequent adsorption of GTF onto the surfaces. Milk also reduced the expression of enzymatic activity of GTF adsorbed onto sHA. kappa-Casein, when present on the surface of sHA, reduced the adsorption of GTF activity onto sHA, resulting in reduced glucan formation. alpha-Casein had no effect on the adsorption of GTF onto sHA or on subsequent glucan formation. Both milk and kappa-casein reduced activity of the enzyme in solution. The presence of milk and kappa-casein fractions on the surface of sHA and in solution with GTF can clearly modulate glucan formation in vitro.