COMBINED EFFECTS OF SUNLIGHT AND TITANIUM DIOXIDE NANOPARTICLES ON DIETARY ANTIOXIDANTS AND FOOD COLORS
Lo, Yangming M
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The breakthroughs in material science have enabled industrialized fabrication and production of nanomaterials. To date, nanoscale materials have been shown to exhibit improved functionalities, providing numerous novel applications. Titanium dioxide (TiO2) nanomaterials have been widely utilized in the food industry due to their unique properties under light. Upon light irradiation, TiO2 nanoparticles (NPs) generate highly active reactive oxygen species (ROS) therefore can be potentially used as light tunable antibacterial packaging materials. Moreover, it has also been reported that a considerable amounts of TiO2 NPs is found as an ingredient in food, cosmetics, personal care, and pharmaceutical products. With improved photoactivity, nano TiO2 generates higher amounts of ROS upon light irradiation that can result in oxidative damage. The present study investigates the combined effect of sunlight irradiation and TiO2 nanoparticles (NPs) on sensitive antioxidants and food colors. Upon simulated sunlight irradiation, TiO2 NPs weakened the radical scavenging ability of antioxidants by photocatalytic decomposition or surface adsorption. The decomposition of a widely used food azo dye FD&C Yellow No. 5 (tartrazine) by sunlight activated TiO2 NPs was also investigated. The mechanism is pH dependent, involving the depletion of two main ROS species, hydroxyl radical and singlet oxygen. Compared with the photocatalyst TiO2 sample P25, food-grade TiO2 NPs also showed strong ROS promoting ability and resulted in the degradation of selected synthetic dyes, including tartrazine, allura red and sunset yellow, as well as the semi-synthetic food color chlorophyllin sodium copper salt. Thus, TiO2 NPs should be used with caution when added to or used in contact with food ingredients that depend solely on the existing antioxidants and colors in the system. The ability of TiO2 to generate ROS was found to be phase-dependent. The rutile phase TiO2 generated the least amount of ROS when compared to anatase phase and did not lead to noticeable color degradation in the studied light irradiation period. Thus, when possible, rutile phase TiO2 should be used in food as it provides a more stable system compared to anatase and mixed phases. The results in this study provide clear insights on setting up proper protocols for evaluating and administrating nanosized TiO2 in food uses.