Abstract: The aim of the research was to clarify the difference in the antioxidant activity of peptides derived from the in vivo digestion and in vitro processing of proteins, and further to verify the necessity of the in vitro processing of proteins for preparing antioxidant peptides. The antioxidant activity of egg white peptides derived from simulated gastrointestinal digestion and alkaline protease treatment were compared by chemical methods in vitro. Potent bioactive peptides with a molecular mass less than 1 kDa were isolated and sequenced from the alkaline protease hydrolysate and their protective effect on oxidative damage induced by H2O2 in human hepatoma cells (HepG2) was evaluated. The results showed that the antioxidant activity of the alkaline protease hydrolysate was significantly higher than that of the simulated gastrointestinal digestive products and untreated egg white protein. The antioxidant activity of both the enzymatic hydrolysate and the digestive products was negatively related to their molecular masses and significantly dose-dependent. The peptides with a molecular mass less than 1 kDa from the alkaline protease hydrolysate could effectively inhibit the production of reactive oxygen species induced by H2O2 in HepG2 cells, thereby preventing oxidative stress injury and apoptosis in cells. Three tetra-peptides, FYCP, YCPI and YLPR, were identified by ultra performance liquid chromatography/tandem mass spectrometry, all of which had good antioxidant activity. To a certain extent, this study provides an experimental basis for egg deep processing.

Key words: in vitro processing; simulated gastrointestinal digestion; egg white protein; peptide; antioxidant activity