Screening of ACE inhibitory peptides in digestive products of TGase-induced GCSG and evaluation of their absorption and transport properties.

The digestion characteristics of grass carp skin gelatin (GCSG) with varying degrees of cross-linking induced by transglutaminase (TGase) were investigated. Specific peptide segments with potential angiotensin-converting enzyme (ACE) inhibitory activity were screened from the digestive products of GCSG with a medium crosslinking degree (45.89 ± 0.99%) which had the most abundant digestive peptide segments. Then they were synthesized to confirm their ACE inhibitory efficacy. Additionally, the absorption and transport mechanisms of the active peptides were examined. The findings revealed that the resistance of cross-linked gelatin to digestion was primarily evident during the intestinal digestion phase, with no significant alterations in nutritional quality. Two specific active peptides, PK and GK, were identified, both demonstrating ACE inhibitory activity. GK exhibited greater inhibitory potency, superior permeability and higher bioavailability compared to PK. The degree of ACE inhibition remained comparable after both peptides traversed the Caco-2 monolayer membrane. PK was primarily transported via paracellular diffusion and endocytosis, whereas GK employed a mixed mechanism involving paracellular diffusion, endocytosis and the PepT1 pathway.