Native, but not thermally denatured lactoferrin solubilizes iron in the presence of bicarbonate ions

Abstract

Lactoferrin (Lf) can solubilize more than a 70-fold molar equivalent of iron in the presence of bicarbonate anions. Iron solubilized by Lf (FeLf) is a useful food product for iron fortification, preventing anaemia with no risk of toxicity. However, the mechanism underlying this iron solubilization is not yet well understood. The objective of this study was to investigate the effects of thermal treatments on the iron-solubilizing capacity of Lf in the presence of sodium bicarbonate. Lf was subjected to thermal treatment at 50–80 °C for 10 min, and the Lf heated to over 70 °C was precipitated by the addition of Fe(III). No precipitation was observed in FeLf-like mixtures of heated Lf when various other cations were substituted for Fe(III): Cu(II), Zn(II), Mg or Na. The precipitation was related to the degree of thermal denaturation of Lf, accompanied by the formation of high-molecular-weight aggregates as disulphide bonds were established. Transferrin, α-lactalbumin and β-lactoglobulin did not solubilize Fe(III), suggesting that the Fe(III)-solubilizing capacity is characteristic of Lf. In conclusion, native Lf is responsible for iron solubilization in the presence of bicarbonate anions. Owing to the application of native Lf to the manufacture of FeLf, FeLf can improve specific food products by supplementing their iron content.