Distribution of Added Iron and Polyphosphate Phosphorus in Cow's Milk

The distribution of iron and polyphosphate phosphorus added to cow's milk was investigated by both analytical and radiochemical techniques. Whole milk was separated isoelectrically and/or centrifugally into three major fractions, cream, casein, and whey, after the addition of ferripolyphosphate and other iron or polyphosphate compounds. Casein, a phosphoprotein, had a greater affinity for iron binding than for phosphorus binding: 85 to 95% of the iron and 50 to 5570 of the phosphorus was bound to acid-precipitated casein; and when the casein was obtained by centrffugation, 60 to 70% of the iron was micellar-bound while 50 to 55% of the phosphorus was bound by micelles.