Characterization and Quantification of Zinc Oxide and Titanium Dioxide Nanoparticles in Foods

There has been growing concern in recent years about contamination of foods by engineered nanoparticles (NPs) due to their increasing applications in food packaging materials, pesticides, and other products. In this study, we report a systematic approach to detect, characterize, and quantify engineered NPs (i.e., zinc oxide (ZnO) and titanium dioxide (TiO2) NPs) in food products. A series of concentrations of ZnO and TiO2 NPs from 0.05 to 1 wt% were spiked into corn starch, yam starch, and wheat flour. The presence of engineered NPs in foods was detected and measured by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and transmission electron microscopy. The average sizes of ZnO and TiO2 NPs were around 38 and 40 nm in diameter, respectively. Most ZnO NPs were in either spherical or rod-like shape, while most TiO2 NPs were in a spherical shape. The concentrations of engineered NPs in food samples were measured by inductively coupled plasma optical emission spectrometry. Calibration curves were plotted for quantification of NPs in foods (R (2) = 0.984 and 0.995 for ZnO NPs in corn starch and wheat flour, respectively; R (2) = 0.992 and 0.998 for TiO2 NPs in yam starch and wheat flour, respectively). The results of this study could help develop systematic methodologies for detection, characterization, and quantification of NPs in food matrices.