Multi-technique approach for the characterization of titanium dioxide color additive

Titanium dioxide (TiO₂) has recently gained attention after the European Union banned its use as a food additive, due to a concern for potential genotoxicity of TiO₂ particles that cannot be ruled out. Thus, particle size distribution and other physicochemical properties were a crucial part of TiO₂'s safety evaluation. This study compares the physicochemical properties of TiO₂ used to color food in the US (i.e. TiO₂ color additive) with those similar to Unitane® O220 grade TiO₂ samples used in a 2-year oral carcinogenicity study. A combination of various analytical techniques (dynamic light scattering (DLS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy) and different sample preparation methods (shaking and sonication of the aqueous dispersions) were used for the characterization. Although differences in particle size distributions based on DLS analysis were observed between the shaken Unitane ® O220 samples and the shaken TiO₂ color additive, no distinct differences were found in sonicated samples. Regardless of the sample type and sample preparation method, TEM image analysis revealed the minimum particle size ranges from 14 nm to 73 nm and the maximum particle size ranges from 292 nm to 704 nm. SEM analysis showed similarity in the morphology of all the samples, although elemental impurities were observed in the Unitane ® O220 samples. Raman spectroscopic analysis revealed all TiO₂ samples were in anatase form. A pH-dependent zeta potential analysis showed similarities among TiO₂ color additives and one of the Unitane® O220 samples. Despite some differences, the physicochemical properties of all TiO₂ samples were comparable. These results fill existing knowledge gaps regarding the presence of nanoparticles in TiO₂ color additive, guiding regulatory decisions and safety evaluations.