Influence of pH, temperature and concentration of calcium sequestering salts on the solubilisation of individual caseins and minerals from rennet casein

The effect of the calcium sequestering salts (CSS) disodium phosphate (DSP), trisodium citrate (TSC) and sodium hexametaphosphate (SHMP), pH (5.8 or 6.7), and heat treatment (90 °C for 5 min) on the solubilisation of individual caseins and minerals from 5% (w/w) rennet casein suspensions was studied. Levels of non-sedimentable caseins increased up to 150 mM DSP, 50 mM TSC and 10 mM SHMP, after which they plateaued or decreased. Higher levels of non-sedimentable caseins were found at pH 6.7 than at pH 5.8, whereas heating reduced levels of non-sedimentable caseins, Ca and P. Non-sedimentable Ca decreased with increasing level of DSP but increased with increasing level of TSC and SHMP. The results suggest different mechanism for different CSS; DSP may act through forming insoluble Ca-phosphate complexes, whereas TSC likely forms soluble Ca-citrate complexes and solubilises phosphate. SHMP likely cross-links caseins via calcium-casein phosphate complexes, enabling interaction with cations and caseins simultaneously.