Identification and characterization of inorganic food additives and pearlescent pigments in sprays for food decoration by STEM-EDX

Abstract

Food colorants are applied in commercial products and domestic cooking to enhance the appearance of food. To obtain specific hues, inorganic food additives containing (nano)particles are mixed in varying concentrations, and pearlescent pigments consisting of mica platelets coated with a layer of titanium dioxide and/or iron oxide particles, are applied to provide glitter effects1. For control and risk assessment of multi-constituent substances and mixtures, characterisation of the fraction of small particles, including the particle size distribution, is needed for each single constituent or each component in the mixture2. This is challenging for control laboratories and only limited guidance is currently available3. This study developed electron microscopy-based methods to identify and characterize the particles of individual components in eight commercially available food-decoration sprays of different colours, containing mixtures of food additives and pearlescent pigments. No dispersion protocols or purifications steps were applied to optimally assess the properties of the particles consumers are exposed to. Samples were prepared by spraying 5mL in a glass vial and coated on EM-grids using the grid-on-drop method. Scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDX) allowed identifying particles of separate components, including potassium aluminium silicate-based pearlescent pigments, vegetable carbon, rutile titanium dioxide (nano)particles, iron oxide (nano)particles and aluminium containing (nano)particles by their elemental composition. Their presence and relative concentration varied between spray colours. Often the layer of titanium dioxide particles detached from the mica, and titanium dioxide particles were also observed forming near-spherical aggregates. STEM-EDX tomography allowed identifying particles of overlapping components and examining the structure of the pearlescent pigments in 3D. The presence of a fraction of nanoparticles in each component was demonstrated based on their particle size distributions. The methods and findings support regulatory bodies to assess and control possible health risks of mixtures of (nano)particles present in the food&nbsp;chain.</p