The casein phosphopeptides (CPP) are approximately 10% (w/v) of the protein casein. They are tasteless, have low antigenicity, and can be purified as CPP-ACP complexes from a casein enzymatic digest by filtration. CPP-ACP has been recognized as safe by the Food and Drug Administration of the United States of America and other regulatory bodies around the world and can be incorporated into oral care products and foods.
Four major bovine CPPs containing the sequence -Ser(P)-Ser(P)-Ser(P)-Glu- Glu-, where Ser(P), have been shown to stabilize high concentrations of calcium and phosphate ions in metastable solution supersaturated with respect to the calcium phosphate solid phases (at acidic and basic pH (Cochrane et al., 2008). A 1% CPP solution at pH 7.0 can stabilize 60 mM calcium and 36 mM phosphate. Additionally, stabilization of calcium phosphate phases by CPP has been shown in the presence of fluoride ions (Cochrane et al., 2008).
CPPs bind more calcium and phosphate ions than can be attributed to just the calcium-binding motif -Ser(P)-Ser(P)-Ser(P)-Glu-Glu-, indicating that other acidic residues of the phosphopeptide sequence contribute to the stabilization of calcium phosphate. This interaction prevents growth of the calcium and phosphate ion clusters to the critical size required for nucleation and phase transformations (Cross et al., 2005). This is similar to the properties of statherin; however, the capacity of the casein phosphopeptides is significantly greater than that of statherin, due to the higher content of phosphoseryl and other acidic residues. In solution, an equilibrium exists between free and CPP-bound calcium, phosphate, and fluoride ions. This equilibrium is dependent on environmental factors such as pH, ion concentration, and the presence of competing binding surfaces for the CPP (Cochrane et al. 2008). CPPs only weakly bind calcium and phosphate ions, thus allowing for a dynamic equilibrium between free and CPP-bound ions. This therefore provides a reservoir of bioavailable ions.
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