Phosphate salt-induced structure formation in casein suspensions

The influence of 0.6–1.0 mEq/g casein of the phosphate-based calcium sequestering salts (CSS) pyrophosphate (PP), orthophosphate, and polyphosphates, on the properties of micellar casein isolate (MCI) and sodium (NaCas) and calcium (CaCas) caseinate suspensions containing 5–10 % casein was evaluated at 20 and 40 °C at pH 6.0–7.4. Structural characterizations included measurement of viscosity measurements and NMR transverse relaxation time (T₂) and cryo-TEM. Overall, viscosity increased with increasing casein concentration, PP level, and pH. The highest viscosity for MCI was observed at 1.0 mEq PP/g casein. The polyphosphates sodium tripolyphosphate and sodium hexametaphosphate had far less effect on MCI viscosity. PP addition did not notably affect the viscosity of NaCas suspensions, indicating that calcium may contribute strongly to PP-induced increases in the viscosity of casein systems. The combined effect of temperature and pH significantly influenced the viscosity of MCI-5 % and CaCas suspensions, especially at higher CSS concentrations. NMRand cryo-TEM analyses supported these findings, revealing weaker structures in NaCas and PP-induced crosslinks or dense networks depending on pH, correlating with viscosity changes. This investigation provides valuable insights into casein-CSS interactions, with potential benefits for dairy processing and optimization.