TiO2 Alternative Coatings for Ferric Pyrophosphate Premixes: Stability and Bioaccessibility Relative to Ferrous Fumarate

Titanium dioxide (TiO2) is widely used to mask the color of iron fortificants in double fortified salt (DFS) and in other foods such as candies and mints, but its regulatory status has prompted the search for alternatives. In 2021, the European Food Safety Authority banned TiO2 due to genotoxicity concerns. This study evaluated TiO2 alternatives, CaCO3, MgCO3, ZnO, CaSO4, Opadry, and Nutrafinish blends (commercial coatings of CaCO3 and HPMC), for masking the color of extruded ferric pyrophosphate (FePP) formulations, including those with iron absorption enhancing adjuncts (Na2EDTA, citric acid (CA), trisodium citrate (TSC)) and without adjuncts. Coated premixes were assessed for color uniformity (ΔE), core coverage and in vitro iron bioaccessibility. Successful premixes were stored in iodized salt and iodine retention of fortified salt after nine months of storage at elevated temperature and humidity was assessed. Effective color masking was achieved with 25% ZnO, 45% CaCO3, 55% MgCO3, 65% CaSO4, 25% Opadry, and 25% Nutrafinish 002, all with 15% soy stearin. FePP premixes containing CA/TSC premixes showed improved color uniformity compared with Na2EDTA formulations. Iodine retention exceeded 50% in most formulations, indicating acceptable shelf life. Iodine loss at elevated temperatures was primarily attributed to increased diffusion through coating defects and subsequent reaction between exposed iron and iodate, rather than complete liquefaction of the fat overcoat. Iron release followed pseudo-first-order kinetics, with CaCO3 > ZnO > CaSO4 in solubility and bioaccessibility. These findings demonstrate that TiO2-free coatings can provide effective color masking, maintain iodine stability, and support iron release in FePP-based DFS, offering viable pathways for regulatory-compliant, consumer-acceptable formulations.