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.

碳酸氢盐溶液中乳铁蛋白对铁的溶解作用

摘要 在碳酸氢盐溶液中乳铁蛋白(Lf)可以溶解超过其自身摩尔浓度70倍的铁。生成的LF与铁的复合物(FeLf)通常在食品中作为铁的强化剂用来预防贫血。但是人们对Lf溶解铁的机制认识还是非常有限。本文研究了在碳酸氢钠存在下,热处理对Lf溶解铁的影响。Lf分别在50∼80 °C下处理10 min,然后在70 °C下加入Fe(III)沉淀热处理过的Lf。当用其它阳离子Cu(II)、Zn(II)、 Mg、Na代替Fe(III)时,没有观察到生成类似的FeLf混合物。生成沉淀的量与Lf热变性的程度有关,原因是二硫键的作用Lf形成了高分子凝聚物。转铁蛋白、α-乳白蛋白和β-乳球蛋白不具有溶解铁的能力;能够溶解Fe(III)是Lf蛋白特有的性质。因此,在碳酸氢盐溶液中,天然的Lf能够溶解铁,采用天然Lf生产的FeLf复合物可以作为补铁添加剂用于特定的食品中。