The intake of TiO₂ and SiO₂ nanoparticles from food additives E171 and E551 raised concerns among European Food Safety Authorities (EFSA). Scientific studies highlighted potential adverse effects on human health, leading to the provisional ban of E171 [1] and the reevaluation of E551 [2]. Further research is needed to clarify the effects of these nanoparticulate fractions found in these additives. Therefore, the objectives of this work are to study the actual content of TiO₂ and SiO₂ nanoparticles in three food confectionary matrices, their transformation in the gastrointestinal tract, bioaccessibility, cytotoxicity, and migration into the bloodstream.

The evaluation of changes in size and concentration (both mass and particle) of these (nano)particles during the stages of in vitro gastrointestinal digestion and in aqueous extracts of the confectionaries was conducted using spICP-MS. No significant differences were observed in the average size of TiO₂ between aqueous extracts and digestion stages. However, SiO₂ particles appear to undergo agglomeration or aggregation under in vitro conditions.

Bioaccessibility studies of the intestinal fractions of the food samples revealed a low content of both types of (nano)particles, which did not exceed 6%. Once the bioaccessible intestinal extracts were characterized, both in nanoparticulate (spICP-MS) and ionic (ICP-MS) content, cytotoxicity was evaluated on the Caco-2 cell line using MTT assays at exposure times of 4 and 24 hours. Experiments using commercial standards of ionic Ti (20 and 40 µg L^-1) /Si (200 and 1000 µg L^-1) and TiO₂/SiO₂ (nano)particles (10⁶-10⁷part g^-1) at the concentrations found in the intestinal extracts did not result in a significant decrease in cell viability. However, a cytotoxic effect was observed when exposing the cells to the food intestinal extracts, as cell viability decreased from 83±4 % at 4h to 25±5 % at 24h of exposition time. These results highlight the influence of the complex food matrix on cell viability.

The migration of these nanoparticles across the intestinal membrane was evaluated using spICP-MS at the same exposure times as the MTT assay, analyzing both apical fractions (internal part of the intestine) and basal fractions (bloodstream) of the Transwell inserts. spICP-MS analysis showed that both types of (nano)particles can cross the intestinal membrane after 4 hours of exposure (71-90 % for TiO₂ and 43-80 % for SiO₂), being able to be distributed in the organism. However, this migration is influenced by the food matrix as the exposure time increases.