Cloud point extraction and characterization of zinc oxide nanoparticles isolated from infant milk formulas

The increasing presence of nanoparticles in food products, especially in those consumed by sensitive populations like infants, raises justified health concerns. The presence of zinc oxide nanoparticles (ZnO-NPs) in three different commercial infant milk formulas were analyzed. In addition, one maternal food supplement was included in this study. Notably, existing regulations lack specificity regarding the size distribution of nanoparticles (NPs) and the maximum permissible concentrations in commercial infant products. Except in one sample, the total zinc content exceeded the reported amount in the nutritional label, which varied from 34 to 119 µg/g. This work validated the cloud point extraction (CPE) technique for the effective isolation of ZnO-NPs from the selected products. CPE was then used to evaluate the ZnO-NPs concentrations in commercially available infant formulas and maternal supplements. Using inductively coupled plasma optical emission spectrometry (ICP-OES), the ZnO-NPs and total Zn concentrations were determined. The ZnO-NPs concentration ranged from 16 to 39 µg/g, representing a considerable portion of the total zinc content. Transmission electron microscopy (TEM) analysis indicated the presence of nanoparticles with an average diameter of 6.3 nm. The NPs size could determine their cell internalization, and thus, the potential cytotoxic effects are discussed. These findings underscore the need for rigorous isolation and quantification of nanoparticles from infant milk formulas, and as an inevitable first step for in vitro and in vivo toxicity studies to address the potential health impact of nanoparticles in food products.