The impact of simulated gastrointestinal digestion in vitro on the biological activity of walnut protein: An exploration of the mechanism concerning structural alterations and the release of bioactive peptides

This study aimed to investigate the bioactivity and structural characteristics of walnut protein hydrolysates prepared by simulated gastrointestinal digestion in vitro (WPH-GI). Moreover, it aimed to identify bioactive peptides in WPH-GI, using LC-MS/MS and database-driven search techniques. The results indicated that WPH-GI exhibited stronger antioxidant activity and inhibitory activities against ACE, α-glucosidase, α-amylase and thrombin than WP. Compared to walnut protein (WP), WPH-GI exhibited maximal enhancements of 33.2% in ABTS · + scavenging ability, 71.2% in hydroxyl radical scavenging ability, 40.2% in ACE inhibitory ability, 30.2% in α-amylase inhibitory activity, 21.1% in α-glucosidase inhibitory activity, and 18.4% in thrombin inhibitory activity. We found that WPH-GI's stronger bioactivities may be due to its loose, flexible molecular structure with numerous exposed hydrophobic groups. Furthermore, WPH-GI contained many bioactive peptides, including 33 peptides with high biological activity identified. In conclusion, consuming walnuts is beneficial for health, largely because of the enhanced biological activity of WP after digestion as a result of molecular structural alterations coupled with the release of active peptides. The results of this study lay a theoretical foundation for the health benefits of WP consumption and promote the high-value utilization of walnut meal. • WPH-GI, the digestive product of WP, exhibited superior bioactivities than WP. • WPH-GI had flexible molecular structure with numerous exposed hydrophobic groups. • WPH-GI was rich in peptides, and 203 peptides were identified. • A total of 33 small peptides are expected to exhibit high biological activity.