Fabrication and characterization of whey protein-tannic acid-ferrous ion complexes with improved iron stability and bioavailability.

Conventional food iron fortification strategies face great challenges due to the instability and lower bioavailability of Fe2+. This study fabricated a whey protein isolate-tannic acid-ferrous ion (WTF) complex and systematically investigated its formation mechanism and characteristics. The results indicated that tannic acid non-covalently bound to whey protein, and Fe2+ synergistically promoted the structural reorganization. This interaction led to a decrease in protein α-helix content accompanied by an increase in the proportion of β-structure, along with a decrease in thermal denaturation temperature and surface hydrophobicity. Additionally, WTF significantly reduced the rapid release of iron in the gastric phase (32.2-39.9%), while showing a relatively gentle release behavior (70-78%) in the intestinal phase. Importantly, Fe2+ remained above 80% of the released iron, effectively inhibiting oxidation. Caco-2 cell assays demonstrated good biocompatibility, with cell survival exceeding 85% across all treatments. These findings provided a new insight into iron fortification with fine stability and bioavailability.