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Published on February 7, 2022 by Jenny Maat

As of May 6th 2021, the European Food Safety Authority (EFSA) no longer considers titanium dioxide E171 as safe for use as a food additive due to concerns for genotoxicity. RheoCube can help in finding an alternative for these TiO2 particles.

Titanium dioxide in foods

Titanium dioxide, or TiO2, is used as an ingredient in many different products. It is most commonly used as a pigment, for instance in paints, and, to a lesser degree, in cosmetics like sunscreen or toothpaste. Another common application is as a colorant in food. Here, it is often applied to make food more visually appealing, or to give color to food that would otherwise be colorless. The compound is very bright and has a very high refractive index, making TiO2 an effective opacifier. This means that if it is added to a transparent material, the amount of light that passes through that material will be reduced, making the product more opaque. This property of TiO2 is used in baked goods, broths, sauces and soups among others.

Besides adjusting the look of food, TiO2 can also be used as a flavor enhancer in a variety of non-white foods, including dried vegetables, nuts, seeds, and mustard, as well as beer and wine. On top of that, it can be used to improve the texture of food, for instance in dairy products. The presence of TiO2 can change the flow behavior of the product and thereby also it’s texture and mouthfeel. The TiO2 food additive is commonly referred to as E171.

No longer considered safe in foods

It was already known that TiO2 powder poses a health risk when inhaled, but less was known about digestion. Initially the large particles that are contained in E171 did not raise any concern. This changed when researchers discovered that food-grade TiO2 always contains a fraction of nano-sized particles (diameter smaller than 100 nm) [1]. The white powder used consists of small crystalline particles with an average size of about 220 nm. But the particle size distribution was very wide and contained between 17-35% of nano-sized particles by number. This was an inevitable byproduct of the manufacturing process. When it was shown that these nanoparticles could cross the intestinal wall in animals after digestion, the French government raised concerns. After additional research showed that there was not enough evidence to prove TiO2 nanoparticles were safe for ingestion by humans, it was banned from use in food products in France in 2020 [2].

According to EU law, a food additive may be authorised if it does not pose a safety concern to the health of consumers. The results of the research done in France indicated that there could be a concern for consumer safety after all. To try and gain more insight into the matter, a series of further research projects was set up. The goal was to assess the potential danger of TiO2 nanoparticles in E171. The results, however, were not conclusive [3]. Although the amount of particles that could pass the intestines was shown to be low, they may accumulate in the body. Various studies did not find any adverse effects on reproduction or development in humans, although there was evidence that TiO2 may potentially cause inflammation or be neurotoxic. The biggest concern, however, was the potential of the nanoparticles to break DNA. It was this concern for so-called genotoxicity that prompted the EFSA to, as of May 6th 2021, no longer consider E171 to be safe for use in foods.

How RheoCube can help

As already mentioned, the TiO2 particles of E171 can not only improve the look of food products, but also the “feel” in terms of texture and mouthfeel. It not only affects the color and opacity of foods, but also how the product flows: the rheological properties. Now that E171 is no longer considered safe for consumption, alternative colorants are needed. A large drawback is that alternatives like rice starch or calcium carbonate do give the correct color, but have a potentially negative effect on the thickness and texture of the product. This means that switching to an alternative may alter the way soups flow out of cans, how broths are processed, or how a sauce would feel in your mouth when eaten. Properties like product spreadability – whether or not it slides off the spoon easily, or how thick or runny a product is – can influence consumer choice in the supermarket. 

When unsure how to find a replacement for E171 without changing the flow behavior of the product, a virtual prototyping solution like RheoCube can offer help. Gaining insight into why TiO2 behaves the way it does in a fluid, and how this affects the flow, can be of crucial importance in choosing the right alternative. For instance, RheoCube simulations have already shown that a different shape of the titania particles can have a profound effect on their aggregation under flow.

It is also known that food grade TiO2 is polydisperse and thus contains particles with different sizes. This can also change from batch to batch. The effect of particle size distribution on the viscosity of a suspension under flow is a property that can be explored with RheoCube. Figures 1 and 2 show an example of the way the viscosity changes when going from a monodisperse to a bidisperse system of rough TiO2 particles. By replacing a specific volume of smaller particles (blue) by larger ones (orange), the viscosity of the suspension decreases.

In RheoCube the properties of particles are defined at the microscopic level. Virtual particles of a variety of shapes, roughness, and sizes can be created. By including physical chemical properties of the particle surface, interactions with other ingredients in the product can also be studied. These interactions result in a specific microstructure within the product which is responsible for the observed rheological behavior.

By tuning the microscopic properties of the particles, the limits of particle size, shape and physical chemical properties that would still produce a similar flow behavior as the TiO2 particles can be explored. As such, RheoCube offers a versatile tool to find the replacement that may work best, making it easier to comply with EFSA recommendations and creating a safer food product for consumers. 

[1] Hans Christian Winkler, Tina Notter, Urs Meyer, Hanspeter Naegeli, Critical review of the safety assessment of titanium dioxide additives in food, J Nanobiotechnology. 2018 Jun 1, 16(1):51, doi: 10.1186/s12951-018-0376-8. (https://pubmed.ncbi.nlm.nih.gov/29859103/)