Abstract: The purpose of this research is to clarify the change in the antioxidant activity of collagen peptides after digestion and to explore the necessity of bioactive peptide protection during digestion. The relationship between the amino acid composition and structural characteristics of collagen peptides prepared from sheepskin with molecular mass < 1 kDa and their antioxidant activity was investigated. Meanwhile, the changes in the antioxidant activity of collagen peptides before and after simulated gastrointestinal digestion were measured. The results of liquid chromatography-mass spectrometry (LC-MS) and in silico simulated digestion were considered together to investigate the changes of the peptides during digestion, and the protective effect of enterosoluble vacant capsules on the gastric digestion of collagen peptides was evaluated as well. The results showed that the collagen peptides were rich in proline, and the major secondary structure components were random coil and β-sheet, which could be beneficial to the antioxidant activity. The reducing power and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity of the peptides decreased after digestion, while the 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation scavenging capacity increased. This may be ascribed to the different sensitivities of DPPH radical and ABTS radical cation to amino acids. Furthermore, the antioxidant activity of the peptides decreased markedly after digestion, but it was significantly protected by enterosoluble vacant capsules. In a certain sense, this study provides an experimental basis for the protection of antioxidant collagen peptides during digestion.

Key words: collagen peptide extracted from sheepskin; antioxidant activity; simulated gastrointestinal digestion in vitro; digestive protection