Iron fortification of skim milk: Minerals and 57Fe Mössbauer study

Reconstituted skim milk was fortified at 2, 5, 10 and 20 mmol Fe kg−1 with ferric and ferrous chloride iron with or without reversible acidification by injection of CO2 under pressure. Carbonation improved transfer of iron from the soluble to the colloidal phase and accelerated ferrous iron oxidation. 57Fe Mössbauer spectra of the freeze-dried casein micelles collected by centrifugation demonstrated that iron is present in a distorted octahedral coordination and is chelated by phosphate rather than citrate. Milk iron fortification induced several changes in the mineral component of the casein micelles, which are explained by the formation of a ternary complex: inorganic phosphate–iron–organic phosphate.