Effect of sodium hexametaphosphate on heat-induced changes in micellar casein isolate solutions

Micellar casein isolate (MCI) solutions (9%, w/w, casein; pH 6.7) containing 0, 12 or 24 mEq L⁻¹ sodium hexametaphosphate (SHMP) were subject to three different thermal treatments: in-container sterilisation (121 °C for 8 min) and two different continuous flow sterilisation treatments (124 °C for 5 min and 140 °C for 5.8 s). Samples were analysed after 1–60 d storage at 20 and 40 °C for pH, calcium ion activity, turbidity, particle size, viscosity and protein and mineral distribution. SHMP-induced casein micelle disruption in untreated samples was apparent from reductions in turbidity, particle size and increases in sedimentable caseins and calcium, and from strong increases in viscosity. After heating, the pH and viscosity decreased strongly due to the heat-induced hydrolysis of SHMP. SHMP altered casein micelle structure, but during heat treatment and storage, samples with SHMP showed good stability.