Disruption of casein micelles by calcium sequestering salts: from observations to mechanistic insights

In this study, the disruption of casein micelles through the addition of the calcium sequestering salts trisodium citrate (TSC) and sodium hexametaphosphate (NaHMP) was investigated in micellar casein isolate (MCI) suspensions containing 9% casein. TSC- and NaHMP-induced disruption of casein micelles was apparent from decreases in turbidity and increases in non-sedimentable casein and calcium. Changes in particle size were found not to correlate to micellar disruption, presumably due to residual particles dominating intensity-based particle size distributions. Decreases in Ca-ion activity confirmed the Ca-sequestering activity of TSC and NaHMP. However, while both Ca-sequestering salts disrupted casein micelles, their mode of action appears very different, but this could only be distinguished when also considering changes in non-permeable Ca. Whereas TSC acts through forming soluble Ca-citrate complexes and solubilises inorganic phosphate, NaHMP mainly appears to act through peptisation reactions, wherein micellar calcium phosphate (MCP) nanoclusters are disrupted but not solubilised.