Influence of catechin–PAYCS interactions on gastrointestinal structural and bioactivity stability: Key mechanisms in digestive enzymes inhibition

Food-derived bioactive peptides often show instability during digestion, limiting their functional application. Polyphenols can enhance peptide stability via covalent or non-covalent interactions, influencing structure, activity, and digestion behavior. This study investigated catechin (CA) interactions with PAYCS (Pro-Ala-Tyr-Cys-Ser) and their effects on digestive stability and enzyme modulation. Covalent (CA-PS) and non-covalent (CA/PS) complexes were prepared via alkaline and physical treatments. Spectroscopic analysis confirmed distinct binding modes, altering structural stability and fluorescence properties. SEM and particle size analysis revealed that CA-PS formed a more stable network. Digestion studies demonstrated that CA/PS better resisted gastric digestion, while CA-PS exhibited greater stability in the intestine. Under simulated digestion conditions, CA/PS complexes use mixed-type pepsin inhibition to preserve structure in the stomach, while CA-PS employ competitive trypsin inhibition to retain activity in the intestine. These findings suggest polyphenol-peptide interactions modulate peptide digestion and functional activity, providing insights for enhancing bioactive peptide stability in functional foods.