Physico-chemical characterisation of the fraction of silver (nano)particles in pristine food additive E174 and in E174-containing confectionery

ABSTRACT

Silver (E174) is authorised as a food additive in the EU. The unknown particle size distribution of E174 is a specific concern for the E174 risk assessment. This study characterised the fraction of silver (nano)particles in 10 commercially available pristine E174 food additives and 10 E174-containing products by transmission electron microscopy (TEM) and single-particle inductively coupled plasma-mass spectrometry (spICP-MS). TEM analysis showed that all samples contained micrometre-sized flakes and also a fraction of (nano)particles. Energy-dispersive X-ray spectroscopy (EDX) and electron diffraction confirmed that the (nano)particles and micrometre-sized flakes consisted of silver. A higher amount of (nano)particles was observed in the products than in the food additives. In addition, the surface of the micrometre-sized flakes was rougher in products. The median of the minimum external dimension, assessed as minimal Feret diameter, of the fraction of (nano)particles determined by quantitative TEM analysis was 11 ± 4 nm and 18 ± 7 nm (overall mean ± standard deviation), for food additives and products, respectively. Similar size distributions were obtained by spICP-MS and TEM, considering the limit of detection of spICP-MS. The median of the equivalent spherical diameter of the fraction of (nano)particles determined by spICP-MS was 19 ± 4 nm and 21 ± 2 nm (overall mean ± standard deviation), for food additives and products, respectively. In all samples, independent of the choice of technique, the nano-sized particles represented more than 97% (by number) of the silver particles, even though the largest mass of silver was present as flakes.

GRAPHICAL ABSTRACT

KEYWORDS:

• E174
• silver
• particle size distribution
• TEM
• spICP-MS
• food additive

Acknowledgments

The authors would like to thank Marina Ledecq (Sciensano, Uccle, Belgium), Lotte Delfosse, Ronny Machiels, Krissy Brouwers (Sciensano, Tervuren, Belgium) for their technical assistance and the Joint Research Center for giving access to their SEM (JRC, Geel, Belgium). This research was funded by the Belgian Federal Public Service of Health, Food Chain Safety and Environment, grants “NanoAg@” and “RF16/6306 nanofood@”, by EFSA, grant “Physicochemical characterization and exposure analysis of nanomaterials in food additives in the context of risk assessment (GP/EFSA/AFSCO/2017/06 EFSA-Nano)”, and by a doctoral grant in the framework of a Doctoral Fund – Special Research Fund 2019 of Hasselt University.

Supplementary material

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Additional information

Funding

This work was supported by the European Food Safety Authority [GP/EFSA/AFSCO/2017/06 EFSA-Nano]; Federal Public Service, Health, Food Chain Safety and Environment [NanoAg@, RF16/6306]; Hasselt University [R-10069].