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.

A carboxyethyl substituted azacrown ether derivative (CSAE) was intercalated as a second host into a parent host of well-crystallized crystal of Mg-Al layered double hydroxide (MgAl-LDH) by a CSAE/NO 3 ion-exchange reaction. The influence of intercalation temperature on the structures and compositions of CSAE-LDH nanocomposites was investigated. The composites obtained at the temperatures below 70 °C had almost the same CASE contents and layered structures with a basal spacing of about 1.6 nm, corresponding to the vertical orientation of CSAE plane to the LDH layer. The chemical analysis showed that a considerable amount of CO 3 2-(with CO 3 2-/CSAE molar ratio of 1.4) was incorporated in the interlayer of LDH. The CSAE content decreased while CO 3 2content increased with an increase of the intercalation temperature in the region above 70 °C. At 100 °C, a second staging phase of 2.33 nm appeared, attributed to the ordered stacking of the 1.6 nm phase and a 0.77 nm phase produced by the CO 3 2-/CSAE exchange. At higher temperatures, a new phase with a basal spacing of 1.18 nm appeared, which corresponds to the tilt/twisted orientation of CSAE anions in the interlayer. The other second staging phase of 2.08 nm appeared obviously at 150 °C, due to the regular stacking of the 1.18 and 0.77 nm phases. The adsorptive properties for transition metal ions were studied using the 70 and 150 °C reacted composites. The 70 °C reacted one showed higher adsorptivity toward transition metal ions; the adsorptive capacity increased in the sequence of Cu 2þ > Ni 2þ > Co 2þ > Zn 2þ , and distribution coefficient for Cu 2þ was markedly higher than those for the other ions. However, the 150 °C reacted one showed little adsorptivity toward these ions. The adsorption for transition metal ions was accompanied by the intercalation of nearly equivalent amount of nitrate ions. This shows that the interlayer CSAE ions in the 1.6 nm phase act as a second host, but those in the 1.18 nm phase do not.

The structural control involving staging formation was studied in the nanocomposites of macrocyclic tetraazacrown ether carboxylic acid derivative (TECA) and layered double hydroxide (LDH) obtained by an osmotic swelling/restoration process. After NO(3)-type MgAl-LDH was osmotically swollen in formamide, TECA was added, leading to a restoration of the LDH sheets and formation of TECA-LDH nanocomposites. In the wet state, the structure of the composites was homogenous, and the basal spacings of ∼2.0 or 1.8 nm were not changed by the water-washing process that removed formamide and caused the replacement of NO(3)(-) by CO(3)(2-). However, in the drying process, both the orientation of TECA in the interlayer and the formed staging structure varied with the TECA content. The TECA orientation changed from horizontal to tilted/twisted and finally to vertical with interlayer TECA density. The staging structure occurred for samples with both TECA and small inorganic guests coexisting in the interlayer. Third-staging, second-staging, and homogenous structures were observed at TECA/LDH weight ratios of low (0.125 and 0.25), medium (0.5) and large (1 and 2) values, respectively. The decrease of negative charge of TECA ions from -4 to -1 led to the co-existence of small ions (NO(3)(-)) with TECA in the gallery and the formation of a NO(3)(-)-containing staging structure, even at a high TECA/LDH ratio of 2. The study of the influence of CO(3)(2-) on the composite structure indicates that a TECA/CO(3)(2-) ion exchange progressed reversibly and the staging structure formed is thermodynamically stable, depending mainly on the chemical composition of the interlayer guests. The staging formation could be explained by the Daumas-Hérold model, which differs markedly from the Rüdorff model previously proposed for the LDH system. The treatment in formamide of the composite such as T2L+Na(2)CO(3) with staging structure shows that the transformation process is reversible, and these kinds of composites may be used as an adsorbent for some harmful organic solvents.

No abstract

No abstract