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Titanium dioxide could outfox Listeria biofilms

By Jane Byrne , 13-Aug-2010

Nanostructured photocatalysts disinfect contaminated surfaces in combination with ultraviolet (UV) light and could be used to enhance food safety within the plant as well as ensuring efficiency and cost gains, claims new research.

Researchers based at the Department of Food Science and Technology at the Agricultural University of Athens, who published their findings in Food Microbiology found that a method using titanium dioxide (TiO2) photocatalysts along wtih ultraviolent A light is an alternative means for Listeria monocytogenes biofilm disinfection in food processing.

The researchers said that TiO2 particles can catalyze the killing of bacteria by near-UV light, probably due to the generation of highly active free hydroxyl radicals by photoexcited TiO2 particles.

Biofilms

The occurrence of biofilms in food-processing environments can cause post-processing contamination leading to lowered shelf-life of products and potential consumer illnesses.

“Biofilms not only present a considerable hygiene risk in the food industry but also cause economical losses by technical failures in water systems, cooling towers, heat exchangers, etc.

Sessile micro-organisms have advantages in that they are more difficult to mechanically remove from food-contact surfaces and are more resistant to disinfectants compared with planktonic forms,” said the researchers.

The authors note that previous studies have shown rapid formation of biofilms of various L. monocytogenes strains, under static conditions at 37 °C in food production facilities.

They claim that while a great number of disinfectants have been reported as potential agents for controlling biofilm formation, research on alternative methodologies such as advanced oxidation processes is rather limited.

Method

In their study, the authors said they employed different TiO2 nanostructured thin films, which were deposited on surfaces such as stainless steel and glass using the doctor-blade technique.

The researchers explained all the surfaces were placed in test tubes containing Brain Heart (BH) broth and inoculated with L. monocytogenes. Test tubes were then incubated for 10 days at 16 °C in order to allow biofilm development.

After biofilm formation, they continued, the surfaces were illuminated by ultraviolet A light (UVA; wavelength of 315–400 nm).
And they explained that the quantification of biofilms was performed using the bead vortexing method, followed by agar plating and/or by conductance measurements.
Result

The presence of the TiO2 nanoparticles resulted in a fastest log-reduction of bacterial biofilm compared to the control test. “The biofilm of L monocytogenes for the glass nanoparticle 1 (glass surface modified by 16 per cent w/v TiO2) was found to have decreased by 3 log CFU/cm2 after 90 min irradiation by UVA.”

The researchers claim that further developmental work on the use of TiO2 for food plant surface decontamination could result in potent disinfecting solutions.

And they urge additional investigation to optimize the process efficiency and establish protocols for using TiO2 photocatalysts as effective biofilm disinfectant in food processing facilities.

Source: Food Microbiology
Published online ahead of print: doi: 10.1016/j.fm.2010.07.025
Title: Use of titanium dioxide (TiO2) photocatalysts as alternative means for Listeria monocytogenes biofilm disinfection in food processing
Authors: N.G. Chorianopoulos, D.S. Tsoukleris, E.Z. Panagou, P. Falaras, G.-J.E. Nychas

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