Bioavailability of Functional Iron in Protein Microparticles

Background: Iron deficiency remains a major nutritional challenge, partly due to the limited stability and bioavailability of conventional iron formulations in foods and during digestion. In this study, iron–protein microparticles (IP-MPs) based on bovine serum albumin (IA-MPs) and hemp protein (IH-MPs) were developed via coprecipitation and evaluated as food-compatible iron delivery systems. Methods: Iron–protein microparticles (IP-MPs) were fabricated by a coprecipitation technique. The stability of IP-MPs was investigated in a three-phase digestion model. The uptake of IP-MPs by Caco-2 cells as well as the Ferritin concentration in Caco-2 cells were investigated. Results: Particle morphology and size distribution were strongly dependent on the protein matrix, with hemp protein microparticles exhibiting greater size uniformity and higher stability under simulated gastric conditions. In a standardized in vitro gastrointestinal digestion model, both IP-MP formulations preserved iron predominantly in the bioactive Fe(II) state and remained sufficiently intact to reach the intestinal phase. Biocompatibility and iron uptake were assessed using Caco-2 cell monolayers. Neither formulation induced cytotoxic effects, while iron delivered via IP-MPs showed enhanced cellular uptake compared to a commercial iron supplement and ferrous sulfate. The amount of Fe(II) detected in the basolateral compartment of IH-MP and IA-MP samples (1.4 µg and 1.3 µg, respectively) was higher than that observed for Floradix^® samples (approximately 0.7 µg) and corresponded to about 25% of the total iron applied. Functional iron bioavailability, assessed by ferritin formation, was significantly higher for IP-MPs, with hemp protein microparticles yielding the strongest ferritin response. Conclusions: These results demonstrate that iron–protein microparticles, particularly those based on hemp protein, effectively improve iron stability during digestion and enhance cellular iron bioavailability, highlighting their potential for application in iron fortification and functional food systems.