Characterization of Titanium Dioxide Nanoparticles in Food Products: Analytical Methods To Define Nanoparticles

TLDR

Titanium dioxide (TiO2) is widely used as a food additive to improve color and brightness. The study examined seven food‑grade TiO2 materials, 24 food products, and three personal‑care items to quantify TiO2 content and determine the number‑based size distribution of TiO2 particles. Three state‑of‑the‑art techniques—electron microscopy, asymmetric flow field‑flow fractionation coupled with inductively coupled plasma mass spectrometry, and single‑particle inductively coupled plasma mass spectrometry—were employed to assess particle size distributions. All E171 materials exhibited similar 60–300 nm size distributions with 10–15 % of particles below 100 nm, and 24 of 27 products contained 0.02–9.0 mg TiO2/g, with 5–10 % of particles below 100 nm; the methods yielded comparable distributions but were limited to 20–50 nm, biasing against sub‑20 nm particles and preventing compliance with EU nanomaterial definitions.

Abstract

Titanium dioxide (TiO2) is a common food additive used to enhance the white color, brightness, and sometimes flavor of a variety of food products. In this study 7 food grade TiO2 materials (E171), 24 food products, and 3 personal care products were investigated for their TiO2 content and the number-based size distribution of TiO2 particles present in these products. Three principally different methods have been used to determine the number-based size distribution of TiO2 particles: electron microscopy, asymmetric flow field-flow fractionation combined with inductively coupled mass spectrometry, and single-particle inductively coupled mass spectrometry. The results show that all E171 materials have similar size distributions with primary particle sizes in the range of 60-300 nm. Depending on the analytical method used, 10-15% of the particles in these materials had sizes below 100 nm. In 24 of the 27 foods and personal care products detectable amounts of titanium were found ranging from 0.02 to 9.0 mg TiO2/g product. The number-based size distributions for TiO2 particles in the food and personal care products showed that 5-10% of the particles in these products had sizes below 100 nm, comparable to that found in the E171 materials. Comparable size distributions were found using the three principally different analytical methods. Although the applied methods are considered state of the art, they showed practical size limits for TiO2 particles in the range of 20-50 nm, which may introduce a significant bias in the size distribution because particles <20 nm are excluded. This shows the inability of current state of the art methods to support the European Union recommendation for the definition of nanomaterials.