**1. Introduction**

Titanium dioxide (TiO2 ) is a transition metal oxide with two main applications as either pigment or photocatalyst, in many sectors including buildings (self-cleaning windows, cements, paints and anti-fouling paints), paper industry, cosmetics (sunscreens and tooth paste), pharmaceutics (tablets), food (colouring agent) and others (air-purification system, rubbers, inks and ceramics). Pigmentary applications are by far the most important application of TiO2 . The interest in TiO<sup>2</sup> lies in the scattering of visible light controlled by its high refractive index and its granulometry (size and shape). These requirements also apply for food where TiO2 provides a whitening effect. Although this compound has been used for a very long time

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in food products (with a recent re-approval for a permitted use in food by the European Food Safety Agency), the use of titanium dioxide in food has risen some concerns in Western populations due to the presence of nanoparticles, that is, particles having one or more external dimensions in the size range of 1–100 nm. This review chapter targets an audience of practicing researchers, academics and PhD students, who are interested in the food applications of this compound and the reasons of controversy.

#### **2. Use of TiO2 in foods: function, properties and safety**

Titanium dioxide is a food additive without any nutritive value and added in processed foods to provide a whitening effect. It was first approved for use in food by the United States Food and Drug Administration (FDA) in 1966, then by the European Union in 1969, on the basis of the Codex Alimentarius of the Food and Agriculture Organization/World Health Organization (FAO/WHO). When used as a food colouring, it is labelled as E171 in Europe or INS171 in USA. In other fields, it is also called titanium white, Pigment White 6 or CI 77891. Time to time, it was re-evaluated for minor revisions of specifications in 2006, 2009, 2010 and 2012. In particular, the European Union decided in 2006 to allow the crystalline structure rutile in food in addition to the former authorized form anatase (COMMISSION DIRECTIVE 2006/33/ EC of 20 March 2006). Then, it was subjected to an in-depth evaluation in 2016 (EFSA 2016).
