Degradation and antioxidant activities of peptides and zinc–peptide complexes during in vitro gastrointestinal digestion

The degradation characteristics of three peptides (Ser-Met, Asn-Cys-Ser, and glutathione) and their zinc–peptide complexes were studied using a two-stage in vitro digestion model. Enzyme-resistant peptides and zinc–peptide complexes, antioxidant activities, and free amino acids released by digestive enzymes, were measured in this study. The results revealed that the three peptides and their zinc–peptide complexes were resistant to pepsin but not to pancreatin. Pancreatin can partly hydrolyse both peptides and zinc–peptide complexes, but more than half of them remaining in their original form after gastrointestinal digestion. The coordination of zinc improved the enzymatic resistance of the peptide due to lower solubility of complexes and affected the hydrolytic site of pepsin and pancreatin. Zinc–Asn-Cys-Ser, which is highly resistant to enzymatic hydrolysis and maintains Zn in a soluble form, may have potential to improve Zn bioavailability.