Gastric Digesta of Glycated Whey Protein Isolate Inhibits α-amylase Activity and Attenuates Postprandial Glycemic Excursions

The rapid digestion properties of starch can contribute to acute postprandial hyperglycemia, being a key risk factor for vascular complications in diabetic populations. Whey protein isolate (WPI) readily undergoing Maillard reaction (MR) may influence starch digestion and absorption. In this study, glycated WPI was produced via wet-heating-mediated MR with monosaccharides (glucose or fructose), and its effects on starch digestion kinetics and postprandial glycemic response were evaluated. Glycated WPI formed high-molecular-protein aggregates exhibiting increased particle size and enhanced antioxidant capacities. Secondary structural analysis indicated elevated α-helix content and reduced β-sheet content in glycated WPI. Furthermore, the glycated WPI exhibited stable gel-like structure and pseudoplastic fluid behavior. Notably, WPI-fructose conjugates (WPI-F) decreased wheat starch digestion 39.17% during a 4-hour in vitro assay and increased resistance starch content by 46.45%. While intact native and glycated WPI displayed minimal α-amylase inhibitory effect, gastric digesta of glycated WPI (particularly WPI-F) showed significantly ( p < 0.05) α-amylase inhibition through a non-competitive mechanism. In mice models, oral administration of glycated WPI attenuated postprandial glycemia peaks, and the area under blood glucose curve in WPI-F group was significantly ( p < 0.05) lower than that of control and native WPI groups. Unlike bioactive proteins requiring specialized delivery systems for bioaccessibility, glycated WPI derivatives can be orally administered during meals. Gastric hydrolysis of glycated WPI mediates α-amylase inhibition and attenuates postprandial hyperglycemia. These findings position WPI-F as a functional food ingredient with α-amylase inhibitory activity, demonstrating potential for modulating postprandial blood glucose elevation.