Effect of milk and casein on the absorption of supplemental iron in the mouse and chick

Abstract

Milk is an attractive vehicle for introducing iron supplements into iron-deficient infants and children. This study compares the effects of milk and caseins on the whole-body absorption of radioactive iron complexes in an attempt to resolve the controversy over whether milk and its constituent phosphoproteins seriously impair iron absorption. Evidence is presented to clarify the role of the calcium-casein micelles of cow's milk in binding iron donated by the ferric-nitrilotriacetate (NTA) complex. The absorption of iron from isolated Fe(III)-casein complexes was studied in mice as a function of the casein--to--Fe ratio and was compared with the absorption of Fe(III)-NTA at equivalent levels. Even at casein--to--Fe ratios higher than those found in conventional iron-supplemented cow's milk (10-15 mg Fe/qt; casein P:Fe congruent to 34), absorption of iron(III) from the casein or NTA complex was not significantly different. There was no significant difference in the absorption of iron administered to mice and chicks as ferrous ion, ferric-NTA, or ferric fructose; nonfat cow's milk did not inhibit the absorption of these iron compounds. For the chick, in fact, milk significantly enhanced the absorption of iron from the ferric-NTA chelate. In order to affect iron absorption significantly casein would have to be present considerably in excess of that found in conventionally supplemented cow's milk.

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

“…The values of the hyperfine parameters, summarised in Table 3, clearly indicated that iron is present in milk as high-spin Fe 3þ ions in a distorted octahedral configuration. This is in total contradiction with tetrahedral configuration assumed from spectral analysis of iron fortified milk and Fe-phosvitin complex (Carmichael et al, 1975;Gaucheron, 2000;Gaucheron et al, 1997;Hegenauer, Saltman, Ludwig, et al, 1979;Webb et al, 1973). Nevertheless, Webb et al (1973) reported an octahedral coordination structure in Fe-phosvitin complexes set aside by scientists working on milk iron fortification.…”

“…In full-fat milk, iron binds to the proteins present in the fat globule membrane (Fransson & Lonnerdal, 1983;Hegenauer, Saltman, Ludwig, Ripley, & Ley, 1979). Iron is probably bound to caseins by coordination links with the oxygen of phosphoseryl residues, but also to weaker-affinity sites such as Tyr, Trp, Glu and Asp (Carmichael, Christopher, Hegenauer, & Saltman, 1975;Gaucheron, Molle, Leonil, & Maubois, 1995;Hegenauer, Saltman, Ludwig, et al, 1979;Shears, Ledward, & Neale, 1987). For the whey protein fraction, neither the nature of protein nor the type of interaction involved in iron binding has been precisely determined.…”

Influence of calcium depletion on iron-binding properties of milk

“…The iron-binding ability of milk proteins, especially caseins, has been recognized for over 50 yr. King et al (1959) reported that the added iron bound mainly to the serum portion of the milk and later research demonstrated that it bound mainly to the caseins in skim milk (Carmichael et al, 1975;Raouche et al, 2009a). Caseins bind >90% of the iron added to skim milk (Demott and Dincer, 1976).…”

Milk protein-iron complexes: Inhibition of lipid oxidation in an emulsion

“…This served to remove iron from the environment of the oxidizable milk fat and to lower its tendency to oxidize milk fat. Thus, such iron complexes may be suitable iron donors for the fortification of milk in order to preserve its organoleptic stability [2,6]. Recently, the binding of iron (ferrous sulphate) to commercial milk protein products, sodium caseinate and whey protein isolate (WPI), as a function of pH and iron concentration was examined in our laboratory [17].…”