Salt equilibria in nutritional formulae for infants and young children

The distribution of Ca, Mg, K and Na between the sedimentable (200×g), protein-associated and soluble phase of infant formula (IF; n = 46), follow-on formula (FOF; n = 8), junior growing up milk (jGUM; n = 22) and senior GUM (sGUM; n = 16) were studied. For all product classes, virtually all Na and K was in the soluble phase and small amounts were found as protein-associated, i.e., as counterions. Most Mg was also found in the soluble phase, but a notable proportion (20–30%) was found to be protein-associated. Sedimentable Mg was only found in a few samples. Particularly in IF and FOF products, notable amounts of sedimentable Ca were observed; the proportion of protein-associated Ca increased with increasing casein content of samples, but even after correction for casein content, large differences (>2-fold) remained between products. These differences in casein mineralisation can affect physicochemical properties and colloidal stability.