Role of Mucin in Behavior of Food-Grade TiO₂ Nanoparticles under Simulated Oral Conditions

Abstract

Fine titanium dioxide (TiO2) particles have been used as additives (E171) to modify the optical properties of foods and beverages for many years. Commercial TiO2 additives, however, often contain a significant fraction of nanoparticles (diameter <100 nm), which has led to some concern about their potentially adverse health effects. At present, relatively little is known about how the characteristics of TiO2 particles are altered as they travel through the human gastrointestinal tract. Alterations in their electrical characteristics, surface composition, or aggregation state would be expected to alter their gastrointestinal fate. The main focus of this study was, therefore, to characterize the behavior of TiO2 particles under simulated oral conditions. Changes in the aggregation state and electrical characteristics were monitored using particle size, ζ-potential, turbidity, and electron microscopy measurements, whereas information about mucin–particle interactions were obtained using isothermal titration calorimetry and surface-enhanced Raman spectroscopy. Our results indicate that there was a strong interaction between TiO2 and mucin: mucin absorbed to the surfaces of the TiO2 particles and reduced their tendency to aggregate. The information obtained in this study is useful for better understanding the gastrointestinal fate and potential toxicity of ingested inorganic particles.