Polymerization degree-driven impact on digestive enzyme inhibition by proanthocyanidins: mechanistic insights

This work aimed to investigate the inhibitory mechanisms of proanthocyanidins (PAs) with different polymerization degrees (DP) against pepsin, trypsin, lipase, and α -amylase, using enzyme inhibition and kinetic assays, turbidity, fluorescence, FTIR, CD, and SEM analyses. Results showed a significant positive correlation between mDP ranging from 1 to 12 and the inhibitory efficacy against the four enzymes, with the potency order being trypsin ≈ lipase ≈ α -amylase > pepsin. PA-enzyme interactions exhibited multi-site binding mediated by electrostatic interactions, with mixed-type inhibition for trypsin and non-classical inhibition for the others. Importantly, an enzyme-specific DP-related threshold phenomenon was observed. Efficient fluorescence quenching occurred when mDP exceeded 4, 2, 3, and 2.5 for pepsin, trypsin, lipase, and α -amylase, respectively, whereas λ max blue shifts required higher thresholds (4–12.5). Furthermore, high-DP (mDP 12) formed more compact PA-enzyme complexes than low-DP (mDP 2). This study provides mechanistic insights into the enzyme-specific inhibitory differences between low-DP and highly polymerized PAs.