Zinc oxide (ZnO) and silicon dioxide (SiO2) are currently among the most widely used nanoparticles (NPs) in the food industry as food additives. ZnO NPs have been used as an essential trace element zinc supplement, which is crucial for cellular functi...
Zinc oxide (ZnO) and silicon dioxide (SiO2) are currently among the most widely used nanoparticles (NPs) in the food industry as food additives. ZnO NPs have been used as an essential trace element zinc supplement, which is crucial for cellular functions. SiO2 NPs have been used as an anti-caking agent, and the forms of food additive SiO2 NPs include fumed SiO2 NPs and precipitated SiO2 NPs. While NPs have novel properties due to their large surface area to volume ratio, there is growing concern about their potential toxicity. Therefore, it is important to determine physicochemical properties and fate of NPs. However, analytical method for fate determination of ZnO NPs and SiO2 NPs in food or biological matrices have not been clearly suggested.
In this study, the nonionic surfactant Triton X-114 based cloud point extraction (CPE) approach was optimized to detect ZnO NPs and SiO2 NPs as intact particle and ionic forms in commercial foods and biological matrices. The physicochemical properties of the separated particles were analyzed by measuring constituent particle sizes, hydrodynamic diameters and zeta-potentials. The fates of separated ZnO NPs and SiO2 NPs were determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The fates of ZnO NPs and SiO2 NPs in biological systems were determined overall using in vitro Caco-2 monolayer and follicle-associated epithelium (FAE), ex vivo everted intestinal models, and in vivo SD rats.
The results demonstrated that the CPE can effectively separate particles and ionic forms in foods and biological matrices. The major fate of ZnO in powdered foods was a particle, contrary to its ionic fate in liquid beverages. Conversely, the major fate of SiO2 in foods was a particle. ZnO NPs were internalized into cells in both particle and ionic forms, but dissolved into ions over time, probably forming a Zn-ligand complex. ZnO NPs were found to be transported through intestinal barriers and absorbed in the small intestine primarily as Zn2+ ions. The dissolution properties of ZnO NPs were determined to be about 17%-31% in gastric fluid, but SiO2 NPs were almost insoluble (~0.2%). The tissue distribution fate of ZnO NPs and SiO2 NPs was determined to be primarily ionic in form. However, ZnO NPs and SiO2 NPs can be slightly absorbed in particle form at the same time in the liver and the blood. A comparison of the absorption (%) of two SiO2 NPs of different manufacturing methods showed that the absorption (%) of precipitated SiO2 NPs was higher than that of fumed SiO2 NPs. These results indicate that the major fate of ZnO NPs and SiO2 NPs was determined to be of ionic form in the body. However, a portion of ZnO NPs and SiO2 NPs could be absorbed into the body as particles. Therefore, long-term potential toxicity resulting from particle forms cannot be completely excluded.
These findings will be useful for understanding the potential toxicity of ZnO NPs and SiO2 NPs. Moreover, these findings suggest that the CPE approach will be a useful technique to determine the fate of NPs in foods and biological matrices.