In vitro digestion of food grade TiO2 (E171) and TiO2 nanoparticles: physicochemical characterization and impact on the activity of digestive enzymes

Abstract

Titanium dioxide is a food additive that has raised some concerns for humans due to the presence of nanoparticles. We were interested in knowing the fate of TiO₂ particles in the gastro-intestinal tract and their potential effect on digestive enzymes. For this purpose, we analysed the behaviour of two different food grade TiO₂ samples (E171) and one nano-sized TiO₂ sample (P25) through a standardized static in vitro digestion protocol simulating the oral, gastric and intestinal phases with appropriate juices including enzymes. Both E171 and P25 TiO₂ particles remained intact in the digestive fluids but formed large agglomerates, and especially in the intestinal fluid where up to 500 μm sized particles have been identified. The formation of these agglomerates is mediated by the adsorption of mainly α-amylase and divalent cations. Pepsin was also identified to adsorb onto TiO₂ particles but only in the case of silica-covered E171. In the salivary conditions, TiO₂ exerted an inhibitory action on the enzymatic activity of α-amylase. The activity was reduced by a factor dependent on enzyme concentrations (up to 34% at 1 mg mL⁻¹) but this inhibitory effect was reduced to hardly 10% in the intestinal fluid. In the gastric phase, pepsin was not affected by any form of TiO₂. Our results hint that food grade TiO₂ has a limited impact on the global digestion of carbohydrates and proteins. However, the reduced activity specifically observed in the oral phase deserves deeper investigation to prevent any adverse health effects related to the slowdown of carbohydrate metabolism.