Physicochemical properties and digestibility of starch-iron salt complexes under ultra-high pressure and hydrothermal treatment

Iron fortification via oral iron supplementation is a common strategy to alleviate iron deficiency. However, its efficiency is limited by poor palatability and adverse side effects. Consequently, encapsulating iron sources in starch-based carriers is an effective strategy for iron-fortified foods. In this study, ferrous gluconate (FG) or ferric citrate (FC) was incorporated into rice starch, with the starch‑iron salt complexes generated via ultra‑high pressure (UHP) treatment (200, 400 and 500 MPa) or hydrothermal treatment (H). The morphological and physicochemical characteristics and in vitro digestive properties of the resulting complexes were assessed. Overall, the findings showed that iron incorporation markedly enhanced particle size, hydration ability, solubility, swelling capacity and syneresis of the modified rice starch, with the values following the order: H-FG > 500 MPa-FG > 400 MPa-FG > 200 MPa-FG. In contrast, the incorporation of iron salts reduced the elastic modulus (G′), viscous modulus (G″), viscosity and resistant starch (RS) proportion of the starch. Starch-iron salt complexes exhibited favorable processability with typical shear-thinning behavior and tunable freeze-thaw stability, and held promising application potential as iron fortifiers in cereal staples, sauces and frozen foods. Collectively, these findings offer a theoretical basis for the development of iron-fortified functional foods as ingredients.