**3. Conclusion**

With the aim to ensure a healthy food, the knowledge about TiO2 as food additive increased in the last 5 years. Among the large set of TiO<sup>2</sup> samples, E171 food-grade materials have different physicochemical properties from the reference material P25. Indeed, it is characterized by a low specific surface area (around 10 m2 /g), a pure anatase crystalline phase (sometimes traces of rutile), a low isoelectric point (around 4.1 in ultrapure water) mainly related to the phosphate found at its surface, a mean size of around 140 nm with a distribution spanning from 30 to 300 nm and a fraction of nanoparticles comprised between 17 and 36%. Due to the lack of data on E171, the risk assessment of oral exposure to TiO2 has been mainly performed with TiO2 nanomaterials like P25 which possess a different surface chemistry. As TiO<sup>2</sup> has a low absorption rate, it is mostly excreted in the faeces, suggesting that it does not present any toxicity concern. Nevertheless, there is an increasing awareness of proved or suspected deleterious effects of TiO<sup>2</sup> during its transit in the digestive tract, by compromising intestinal homeostasis before absorption in the upper compartments and/ or throughout the entire intestine by the non-absorbed fraction. Albeit increasingly recognized as key players in gut health, mucus and microbiota have often been neglected in food nanotoxicology and should now be more deeply investigated. The link with some intestinal diseases needs to be confirmed as well. For all further studies, the use of food-grade forms of TiO<sup>2</sup> is more relevant than that of the nanomaterial P25.
