Trace element speciation in human milk

Abstract

This paper summarizes speciation results in human milk samples. Information is presented about why these elements were speciated, which techniques were applied, and which speciation results were gained in human milk. We focus on a few selected elements, such as Zn, Se, I, and Mn. Each of these elements is regarded as an "essential" element and of specific importance for newborns. At the end of each element section, we attempt to extract the overall speciation information from the different literature sources. In short, for Zn it can be concluded that this element is bound predominantly to low-molecular-weight (LMW) compounds. Several papers identify the major Zn species as Zn-citrate. A few minor species are identified as well. The pattern of Se speciation seems to be dependent on the nutritional intake. Selenium speciation in milk from slightly Se-depleted regions shows Se bound in the LMW range, ligands were partly identified. In Se-rich regions, Se seems to be associated with proteins, e.g., glutathione peroxidase. The major I species in human milk is iodide, as found by several groups. Other I species, however, were seen as well. The results of Mn speciation from different groups agreed that Mn is to a considerable amount in the LMW fraction. Again, citrate seems to play an important role as ligand.