Preparation and Properties of Iron-Soy Protein Nanocomplexes Based on Coordination

In the present study, in order to broaden the application of iron fortifiers in the food industry, alkali-heat treated soybean protein isolate (HSPI) was reacted with FeSO₄ to fabricate stable iron-containing nanocomplexes. The results showed that the reaction of HSPI with an appropriate concentration of FeSO₄, which was pH dependent, could form stably dispersed nanocomplexes (Fe-HSPI). The size of Fe-HSPI changed with increasing reaction pH, and the color became darker. Fe-HSPI was stable against in vitro digestion, and the binding between protein and Fe²⁺ was maintained during simulated gastrointestinal digestion, which could be beneficial to prevent free iron stimulating the gastrointestinal tract. Herein, Fe-HSPI prepared at pH 7 (Fe-HSPI_{pH 7}) had good homogeneity (polydispersity index, PDI < 0.2) and the content of soluble iron after digestion was more than 80%, showing a remarkable potential for absorption and utilization. The Fe²⁺in Fe-HSPI_{pH 7} mainly combined with the nitrogen atom of the amino group and the oxygen atom of the carboxyl group in HSPI, thereby facilitating the folding of the peptide chain and resulting in the formation of a structure stabilized by disulfide bonds. Compared with FeSO₄, Fe-HSPI_{pH 7} induced a significantly lower degree of lipid oxidation when applied in oil-in-water emulsions, thus exhibiting lower reactivity and having better potential for application as an iron fortifier.