Nanotechnology shows great potential for producing food with higher quality and better taste through including new additives, improving nutrient delivery, and using better packaging. However, lack of investigations on safety issues of nanofood has resulted in public fears. How to characterize engineered nanomaterials in food and assess the toxicity and health impact of nanofood remains a big challenge. Herein, a facile and highly reliable separation method of TiO2 particles from food products (focusing on sugar-coated chewing gum) is reported, and the first comprehensive characterization study on food nanoparticles by multiple qualitative and quantitative methods is provided. The detailed information on nanoparticles in gum includes chemical composition, morphology, size distribution, crystalline phase, particle and mass concentration, surface charge, and aggregation state. Surprisingly, the results show that the number of food products containing nano-TiO2 (<200 nm) is much larger than known, and consumers have already often been exposed to engineered nanoparticles in daily life. Over 93% of TiO2 in gum is nano-TiO2 , and it is unexpectedly easy to come out and be swallowed by a person who chews gum. Preliminary cytotoxicity assays show that the gum nano-TiO2 particles are relatively safe for gastrointestinal cells within 24 h even at a concentration of 200 μg mL(-1) . This comprehensive study demonstrates accurate physicochemical property, exposure, and cytotoxicity information on engineered nanoparticles in food, which is a prerequisite for the successful safety assessment of nanofood products.

Silica nanoparticles (NPs) have been widely used in food products as an additive; however, their toxicity and safety to the human body and the environment still remain unclear. As a food additive, silica NPs firstly enter the human gastrointestinal tract along with food, thus their gastrointestinal toxicity deserves thorough study. Herein, we evaluated the toxicity of food additive silica NPs to cells originating from the gastrointestinal tract. Four silica NP samples were introduced to human gastric epithelial cell GES-1 and colorectal adenocarcinoma cell Caco-2 to investigate the effect of silica sample, exposure dose and exposure period on the morphology, viability and membrane integrity of cells. The cell uptake, cellular reactive oxygen species (ROS) level, cell cycle and apoptosis were determined to reveal the toxicity mechanism. The results indicate that all four silica NPs are safe for both GES-1 and Caco-2 cells after 24-h exposure at a concentration lower than 100 µg ml(-1) . At a higher concentration and longer exposure period, silica NPs do not induce the apoptosis/necrosis of cells, but arrest cell cycle and inhibit the cell growth. Notably, silica NPs do not pass through the Caco-2 cell monolayer after 4-h contact, indicating the low potential of silica NPs to cross the gastrointestinal tract in vivo. Our findings indicate that silica NPs could be used as a safe food additive, but more investigations, such as long-term in vivo exposure, are necessary in future studies.

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