Location: Quality & Safety Assessment ResearchTitle: Photocatalytic degradation of methylene blue and inactivation of gram-negative bacteria by TiO2 nanoparticles in aqueous suspension Author
Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/2013
Publication Date: 12/1/2013
Citation: Wang, J., Li, C., Zhuang, H., Zhang, J. 2013. Photocatalytic degradation of methylene blue and inactivation of gram-negative bacteria by TiO2 nanoparticles in aqueous suspension. Food Control. 34(2):372-377. Interpretive Summary: Microbiological shelf life of raw meat products is very limited at a refrigerated temperature. Many non-thermal methods have been tested and developed to control microorganism populations on raw meat products. Antimicrobial packaging has been drawing special interests, as it is a non-thermal treatment, can continue effectively controlling microbial growth after packaging, and extends food shelf life. TiO2 nanoparticles are a metal oxide with effective antimicrobial activities under UV light and have been tested as a packaging ingredient for food antimicrobial packaging. The objective of this study was to evaluate the effect of TiO2 nanoparticles on the growth of Gram-negative bacteria, which are commonly found on raw meat products, E. coli and P. aeruginosa, in aqueous suspension. An organic dye, methylene blue, was used as a comparison for TiO2 photocatalytic activities. Results show that TiO2 nanoparticles were also very effective with inhibiting growth of both Gram-negative bacteria E. coli and P. aeruginosa. The photocatalytic inactivation towards E. coli and P. aeruginosa showed a similar trend with much higher effectiveness towards E. coli under the same experimental conditions. These results indicate that TiO2 nanoparticles can effectively inhibit Gram-negative bacterial growth under UVA light and may be used as an effective component in antimicrobial packaging for extending shelf life of raw meat products.
Technical Abstract: The photocatalytic degradation of methylene blue (MB) and inactivation of Gram-negative bacteria E. coli K12 and P. aeruginosa by TiO2 nanoparticles in aqueous suspension were studied. TiO2 resulted in significant reduction in MB absorption and a shift of MB absorption peak from 664 nm to 658 nm after a short time of irradiation. The maximum degradation of MB was observed when the concentration of TiO2 in the aqueous suspension was 0.5 g/L. TiO2 was also very effective with inhibiting growth of Gram-negative bacteria E. coli and P. aeruginosa, although it took more than 60 min to observe the inactivation effects. The photocatalytic inactivation towards E. coli and P. aeruginosa by TiO2 showed a similar trend with much higher effectiveness towards E. coli under the same experimental conditions. The inactivation kinetic behaviors could be explained by a modified Langmuir-Hinshelwood model and well fitted to a pseudo-first order kinetic equation. The inactivation rate constants for E. coli and P. aeruginosa were 7.768×106 cfu/(mL•min) and 5.655×106 cfu/(mL•min), respectively. The adsorption equilibrium constant for E. coli was 1.053×10-8 mL/cfu, while it was 1.438×10-8 mL/cfu for P. aeruginosa. These results further demonstrate that in an aqueous system, TiO2 nanoparticles can effectively both degrade organic compounds and inhibit Gram-negative bacteria under UVA light. Compared with the degradation activity of TiO2 towards organic compounds, its antimicrobial activity against Gram-negative bacteria would be delayed by 60 min. The antimicrobial activity of TiO2 against Gram-negative bacteria could vary with bacterial species.