RESUMEN
Differences have been observed in both quantitative and qualitative zinc content in human as well as cow milk and colostrum compared to the milk powder preparations which are commonly used as baby's food. It is noteworth that in unprocessed milk and colostrum zinc was present mainly as casein-dependent element, whereas the remaining part of it consisted of immunoglobulin fraction, and only traces were found in the free state. In milk powders zinc showed concentrations lower than in the natural food, and was present mainly as free or protein-independent element. The immunoglobulin fraction of zinc was practically absent from these preparations, while it was found to be a specific component of the natural food (that is, colostrum and milk from all the species examined in the present study).