Selection of photocatalytic bactericidal titanium dioxide (TiO2) nanoparticles for food safety applications

The main objective of this study was to develop a systematic testing protocol for selecting bactericidal TiO2 nanoparticles (NPs). Photocatalytic bactericidal activity of TiO2 NPs at 1 mg/mL concentration was tested against Escherichia coli O157:H7. The effect of source of NPs (three different commercial samples referred as T1, T2 and T3), bacterial cell wash conditions (1 vs 3 wash), volume of reaction mixture (10, 20 and 30 mL) and intensity of UVA light (1 vs 2 mW/cm2) on bactericidal activity has been determined. Sample T3 was found to be the most effective among the tested TiO2 samples. Increasing the number of cell washes from 1 to 3 increased the log reduction (2.91 vs 4.57). Increasing the light intensity increased the overall log reduction (3.27 vs 4.22). Decreasing the volume of reaction mixture increased the log reduction. This study has identified the best testing protocol for evaluating TiO2 NP bactericidal efficacy as single wash of bacterial cells with a reaction mixture volume of 20 mL and UVA light intensity of 2 mW/cm2. In addition, it was found that photocatalytic oxidation of organic dyes can be used a quick and easier way to screen bactericidal TiO2 NPs prior to actual microbiological tests.