Changes in Zinc in Milk during Enzymatic Digestion

The amount of zinc in human and cow's milk was evaluated in in vitro experiments using gel chromatography on Sephadex G-75 to simulate the action of gastrointestinal enzymes. The HCl-peptic digestion of both types of milk demonstrated that most of the zinc eluted at the same position as Zn(NO3)2. The sequential digestion of both types of milk by pepsin and trypsin demonstrated that most of the zinc eluted at a position corresponding to a molecular weight slightly less than 12, 000. The results suggest that zinc may be liberated in the stomach and that when the pepsin-digested milk passes into the duodenum, which has an alkaline pH and where trypsin is secreted, zinc may bind to substance (s) formed during intestinal digestion. There was no difference between the elution profiles of the two kinds of milk. This indicates that differences in zinc availability in human and cow's milk is not responsible for the molecular weight of zinc-binding substances.