Iron, copper, zinc, calcium, and magnesium in human milk fat

The trace elements iron, copper, and zinc and the minerals calcium and magnesium have been found associated to human milk fat. After solubilization of milk fat globule membranes with detergent, the major part of these elements within the fat fraction were found in the more hydrophilic outer fat globule membrane: Fe 61%, Cu 73%, Zn 64%, Ca 67%, and Mg 71%. Most of the remainder was found in the more hydrophobic inner membrane, while only small amounts of the elements were associated with the core triglyceride fraction. Gel filtration chromatography on Sepharose CL-6B indicates the major iron- and zinc-binding proteins in the outer membrane are xanthine oxidase and alkaline phosphatase.