Characterization of Food-Grade Titanium Dioxide: The Presence of Nanosized Particles

Abstract

Titanium dioxide (TiO2) is widely used in food products, which will eventually enter wastewater treatment plants and terrestrial or aquatic environments, yet little is known about the fraction of this TiO2 that is nanoscale, or the physical and chemical properties of TiO2 that influence its human and environmental fate or toxicity. Instead of analyzing TiO2 properties in complex food or environmental samples, we procured samples of food-grade TiO2 obtained from global food suppliers and then, using spectroscopic and other analytical techniques, quantified several parameters (elemental composition, crystal structure, size, and surface composition) that are reported to influence environmental fate and toxicity. Another sample of nano-TiO2 that is generally sold for catalytic applications (P25) and widely used in toxicity studies, was analyzed for comparison. Food-grade and P25 TiO2 are engineered products, frequently synthesized from purified titanium precursors, and not milled from bulk scale minerals. Nanosized materials were present in all of the food-grade TiO2 samples, and transmission electron microscopy showed that samples 1-5 contained 35, 23, 21, 17, and 19% of nanosized primary particles (<100 nm in diameter) by number, respectively (all primary P25 particles were <100 nm in diameter). Both types of TiO2 aggregated in water with an average hydrodynamic diameter of >100 nm. Food-grade samples contained phosphorus (P), with concentrations ranging from 0.5 to 1.8 mg of P/g of TiO2. The phosphorus content of P25 was below inductively coupled plasma mass spectrometry detection limits. Presumably because of a P-based coating detected by X-ray photoelectron spectroscopy, the ζ potential of the food-grade TiO2 suspension in deionized water ranged from -10 to -45 mV around pH 7, and the iso-electric point for food-grade TiO2 (<pH 4) was significantly lower than that for P25. The presence of other elements in or on the TiO2 (Si content of 0.026-0.062% and Al content of 0.0006-0.810%) was also different from the case for P25 and would influence the environmental fate of TiO2. X-ray diffraction analysis confirmed the presence of anatase and/or rutile in the food-grade materials, and although the presence of amorphous TiO2 could not be ruled out, it is unlikely on the basis of Raman analysis. The food-grade TiO2 was solar photoactive. Cationic dyes adsorbed more readily to food-grade TiO2 than P25, indicating very different potentials for interaction with organics in the environment. This research shows that food-grade TiO2 contains engineered nanomaterials with properties quite different from those of P25, which has previously been used in many ecotoxicity studies, and because food-grade TiO2 is more likely than P25 to enter the environment (i.e., potentially higher exposure levels), there is a need to design environmental (and human) fate and toxicity studies comparing food-grade to catalytic TiO2.

Oral intake of added titanium dioxide and its nanofraction from food products, food supplements and toothpaste by the Dutch population

“…The broad range in the estimation of nanofraction of E 171: the nanofraction of E 171 was estimated at 0.012-0.31% (by mass) by Peters et al (2014). Although the maximum value of 0.31 weight% of Peters et al was chosen to calculate the nanofraction (5100 nm) of TiO 2 (TiO 2 NPs) we acknowledge that there is uncertainty around the true exposure to TiO 2 NPs as the other reported values were higher (Warheit et al, 2015;Weir et al, 2012;Yang et al, 2015), the percentage of 0.31% is possibly an underestimation and may have led to an underestimation of the intake of TiO 2 NPs in the present study. Intake of toothpaste: We assumed no intake from toothpaste by children 46-year-old, adults and elderly, which might result in an underestimation.…”

“…As the anatase form has been accepted as food pigment much longer than the rutile form, it seems plausible that this form is still the most used in food products. Indeed, Yang et al (2015), who characterised samples of food grade TiO 2 from five different vendors that ship to the US and EU, detected the anatase form in all samples and rutile in only one (Yang et al, 2015). The white colour of pigment TiO 2 is best achieved with particles of 200-300 nm, as these give an optimal diffraction of light for this colour (Braun, 1997).…”

“…nanoparticles (NPs)) (TDMA, 2013). Indeed, the presence of NPs in E 171 and in several food products containing E 171 (such as chewing gum, coloured hard-shell candy and icing) has been reported (Peters et al, 2014;Weir et al, 2012;Yang et al, 2015). Weir et al (2012) reported that approximately 36% of the number of particles in E 171 (from one supplier) were5100 nm in at least one dimension.…”

Is nano safe in foods? Establishing the factors impacting the gastrointestinal fate and toxicity of organic and inorganic food-grade nanoparticles

“…The most common crystalline forms in foodgrade titanium dioxide particles are anatase and rutile, which are polymorphic forms that have different crystal packing and physicochemical properties. 60 The surface composition of foodgrade titanium dioxide particles may also vary depending on the source, with different levels of phosphorous, aluminum and silica being detected by X-ray analysis. 60 In addition, organic molecules may also be present at the particle surfaces, which will also impact their interfacial characteristics, such as ζ-potential, hydrophilicity, surface energy, and chemical reactivity.…”

Nanoscience and nanotechnologies for biobased materials, packaging and food applications: New opportunities and concerns

“…Investigating titanium dioxide makes it easier, as it is usually at the surface of confectionery and gives a strong signal by Raman spectroscopy when in anatase form. By chance, this form is widely used in food additives (Peters, van Bemmel et al 2014;Yang, Doudrick et al 2014;Dudefoi, Terrisse et al 2017). We thus used this method to discriminate food products containing TiO2.…”