Efficacy of photocatalytic nanocoatings on food contact surfaces to inactivate pathogenic microorganisms
Yemmireddy, Veerachandra Krantikumar
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TiO2 is a promising photocatalyst for use in food processing environments as an antimicrobial coating. The overall goal of this research was to develop physically stable TiO2 nanocoatings with strong bactericidal property on food contact surfaces. A testing protocol was developed to determine the photocatalytic bactericidal activity of TiO2 nanoparticles (NPs) in suspension. Among the tested TiO2 NPs, Aeroxide® P 25 was found to be the most efficient and achieved a 5 log reduction of bacteria in 3h. Type and source of TiO2, bacterial cell harvesting conditions, volume of suspension, and intensity of UV-A light had significant effect on the log reduction. Further, the effect of food organic matter on bactericidal property of TiO2 NPs was investigated. Increasing the concentration of organic matter decreased the bactericidal efficacy of TiO2. A linear correlation was observed between chemical oxygen demand (COD) and total phenolics as well as COD and protein contents. An empirical equation in the form of “Y=me-nX” (where Y is log reduction, X is COD and m, n are reaction rate constants) was able to successfully predict the disinfection kinetics of TiO2 in the presence of organic matter (R2 = 0.944). In the next study, TiO2 coatings having a thickness of 50-100 µm were developed on stainless steel substrates either by dip-coating or painting. Among several tested coating formulations using different binders; TiO2 coatings containing shellac, polyurethane, and polycrylic as binders at 4 to 16 weight percent were physically stable when subjected to adhesion strength, scratch, and wear resistance tests. An indented coupon technique was found to be the most appropriate method to determine the bactericidal property of TiO2 nanocoatings. TiO2 coating with polycrylic showed the greatest reduction followed by TiO2 coating with polyurethane, and shellac. On repeated use of coatings for 1, 3, 5, and 10 times, TiO2 coating with polycrylic was found to be physically more stable and able to retain its original bactericidal property. The results of this research show promise to development of durable photocatalytic antimicrobial nanocoatings on food contact surfaces to help ensure a safe food processing environment.