Controllable preparation of whey protein isolate fibrils-oxidized dextran covalent complex as a delivery vehicle for enhancing iron bioavailability

Iron deficiency remains the most prevalent nutritional disorder worldwide. Conventional ferrous supplements are prone to oxidation into poorly bioavailable ferric iron and may induce free radical damage. To address this, this study developed a novel iron delivery system (WPHF-DEX-Fe) based on the covalent grafting of enzymatically hydrolyzed whey protein fibrils (WPHF) with oxidized dextran. Controlled grafting was achieved via a mild wet-heating Maillard reaction. Ultraviolet-visible spectroscopy (increased A₂₉₄ without a rise in A₄₂₀) confirmed the formation of Schiff bases without significant browning. Grafting induced conformational adjustments in the protein, significantly (p < 0.05) enhancing the antioxidant capacity of the complex; the superoxide anion scavenging efficiency of WPHF-DEX was 2.1 times that of the unmodified protein fibrils (WPF). This system effectively stabilized ferrous iron, with X-ray photoelectron spectroscopy analysis revealing an Fe²⁺ proportion of 77%. After 15 days of storage at 50 °C and 75% relative humidity, its ferrous retention remained at 45.6%, which is 18.6 times higher than that of WPF-Fe. In vitro digestion studies indicated that after rapid iron release in the gastric phase, iron bioaccessibility stabilized under neutral intestinal conditions while maintaining a high proportion of Fe²⁺, suggesting possible re-integration into a stable complex. This behavior is conducive to iron bioaccessibility and may reduce intestinal irritation. Cell experiments confirmed the good biocompatibility of the material, with iron uptake by Caco-2 cells being 1.3 times that of the ferrous sulfate group. These results demonstrate that WPHF-DEX-Fe is a potential nutraceutical carrier capable of synchronously improving iron stability and bioavailability, offering a new strategy for developing efficient iron supplements.