Interaction between calcium and casein hydrolysates: Stoichiometry, binding constant, binding sites and thermal stability of casein phosphopeptide complexes

The ability of a casein hydrolysate rich in casein phosphopeptides (CPPs) to form calcium complexes was studied. An association constant of 125 ± 32 L mol−1 at 25 °C was determined electrochemically, forming 1:1 complexes according to conductivity measurements. Chloride anions increased the affinity for calcium and number of CPPs bound to calcium in solution to more than one. From temperature dependence of the association constant, the enthalpy of binding of calcium chloride to CPPs was determined to be −24 kJ mol−1. Fourier transform infrared spectroscopy confirmed solid state binding of chloride and calcium to CPPs, further showing a positive cooperativity induced by calcium due to opening of the alpha-helix structure of CPPs. In addition, calcium chloride complexation was shown to increase the thermal stability of CPPs according to the results of thermogravimetry differential scanning calorimetry. In conclusion, hydrolysed casein could be considered as a potential enhancer of calcium availability in food.