Criteria to define a more relevant reference sample of titanium dioxide in the context of food: a multiscale approach

ABSTRACT

Titanium dioxide (TiO₂) is a transition metal oxide widely used as a white pigment in various applications, including food. Due to the classification of TiO₂ nanoparticles by the International Agency for Research on Cancer as potentially harmful for humans by inhalation, the presence of nanoparticles in food products needed to be confirmed by a set of independent studies. Seven samples of food-grade TiO₂ (E171) were extensively characterised for their size distribution, crystallinity and surface properties by the currently recommended methods. All investigated E171 samples contained a fraction of nanoparticles, however, below the threshold defining the labelling of nanomaterial. On the basis of these results and a statistical analysis, E171 food-grade TiO₂ totally differs from the reference material P25, confirming the few published data on this kind of particle. Therefore, the reference material P25 does not appear to be the most suitable model to study the fate of food-grade TiO₂ in the gastrointestinal tract. The criteria currently to obtain a representative food-grade sample of TiO₂ are the following: (1) crystalline-phase anatase, (2) a powder with an isoelectric point very close to 4.1, (3) a fraction of nanoparticles comprised between 15% and 45%, and (4) a low specific surface area around 10 m² g^–1.

GRAPHICAL ABSTRACT

KEYWORDS:

• TiO₂
• nanoparticle
• food
• E171
• surface properties

Acknowledgements

The two affiliations are those where the research was conducted. Carole La, Florian Massuyeau and Stéphane Grolleau are acknowledged for their help in performing, respectively, the ICP-AES at the Laboratoire de Planétologie et Géodynamique, and UV-visible reflectance and BET measurements at the Institut des Matériaux Jean Rouxel IMN, both in Nantes, France.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was carried out under the framework of the Labex Serenade [grant number ANR-11-LABX-0064] and of the A*MIDEX project [grant number ANR-11-IDEX-0001-02] funded by the ‘Investissements d’Avenir’ French government programme managed by the French National Research Agency (ANR).