The application of E171 (titanium dioxide) as a food additive has been an issue of debate in the European Union. A detailed physicochemical characterization of the E171 particles can objectify the discussions and is essential in the context of risk analysis.
This work focuses on the physicochemical characterization of 15 pristine E171 materials by transmission electron microscopy (TEM) and single particle inductively coupled plasma mass spectroscopy (sp-ICP-MS) following CEN/TC 352 guidelines. The E171 samples were purchased on the Belgian market or were obtained from European producers.
In optimized conditions, representative TEM micrographs could be recorded and the ParticleSizer image analysis software succeeded in applying noise reduction and background subtraction, allowing robust automatic thresholding and constituent particle detection. The large majority of constituent particles, confirmed to be TiO2 by energy dispersive X-ray spectroscopy (EDX), were reliably detected and measured by the software. The measurement uncertainty budgets of particle sizing by TEM and sp-ICP-MS are in the order of 10% and 16 % (Ucx, k=2), respectively, based on validation studies of a series of representative test materials. The phase of the E171 particles was determined by powder electron diffraction.
Several types of TiO2 particles were found in pristine E171. These types were shown to be applied as well in food products containing E171. All examined E171 food additives contained a significant amount of nanoparticles. In the most dispersed state, the particle size measurements by TEM and sp-ICP-MS agreed well. Eleven E171 materials consisted of anatase. Three materials consisted of smaller rutile TiO2 particles (20-40 nm) coated on mica. One material contained a mixture of anatase and rutile particles.
In future research, the methodology will be implemented in a systematic and larger scale study of E171 food additives and food items containing E171, available on the market.