Use of 31P NMR and FTIR to investigate key milk mineral equilibria and their interactions with micellar casein during heat treatment

The thermal treatment of milk is one of the key processes routinely performed in the dairy industry. Several modifications occur in milk during heating, particularly with respect to its mineral equilibrium. As the temperature increases, the solubility of calcium and phosphate decreases leading to precipitation in the casein micelle as casein phosphate nanocluster. Recently, 31P NMR and Fourier Transform Infrared have been demonstrated to be capable of monitoring changes to its nanocluster. In this study, the effect of temperature on nanocluster during heating of milk to temperatures ranging from 25 °C to 80 °C followed by subsequent cooling were studied. It was also demonstrated that key ionic components of the mineral equilibria behaved differently with temperature, e.g., calcium influence was evident only at lower temperature, while the opposite was the case with phosphate. It was also shown that micellar casein concentration was influential at all temperatures, most notably at lower values.