Application of a thermally stable oat-derived octapeptide LQAFEPLR as an α-glucosidase inhibitor in biscuits

Bioactive peptides are emerging functional ingredients for attenuating postprandial glycemia through the inhibition of carbohydrate-digesting enzymes. This study characterized the synthetically produced oat-derived octapeptide LQAFEPLR (LQ8) and its cyclized variant CLQAFEPLRC (CLQ8), and evaluated their α-glucosidase inhibitory properties and food application potential. Results revealed that both short peptides were highly soluble, thermally stable, and predicted to be non-toxic, although potential allergenicity was suggested based on sequence homology with oat proteins and warrants further validation. At a relatively low concentration (3.1 μg/mL), LQ8 and CLQ8 exhibited α-glucosidase inhibition of 26.4% and 25.0%, respectively. However, the weak dose-response relationship and kinetic observations suggested different inhibitory behaviors, with LQ8 showing a mixed or uncompetitive-like mode and CLQ8 displaying a non-classical modulatory effect against yeast maltase α-glucosidase. These differences may be related to their distinct binding profiles, as docking suggested that the peptides interacted with catalytic or near-catalytic residues through partial or alternative binding modes rather than fully occupying the catalytic pocket. When incorporated into biscuits, both peptides remained bioactive after baking at 160 °C, with biscuit digesta showing α-glucosidase inhibition of 39.3% for LQ8 and 46.9% for CLQ8. Furthermore, both peptides significantly reduced in vitro starch digestibility, as indicated by significantly lower incremental area under curve values for d-glucose release during simulated gastrointestinal digestion compared with the control biscuit. These findings suggest the potential of both peptides as non-toxic, thermally stable, α-glucosidase inhibitory ingredients for incorporation into bakery products aiming to attenuate postprandial glycemic responses.