Multi-talented: Combo Catalyst Stops Listeria Spread, Produces Clean Energy, And May Work Against SARS-CoV-2

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A food safety expert and mechanical engineering professor from the University of Houston recently teamed up to tackle a serious problem in the food industry—listeria contamination. And while listeria monocytogenes is certainly not a concern in mechanical engineering, the findings have implications for Francisco Robles’ broad research efforts.

“Renewable energy is our main target, followed by a series of other applications, such as water purification and environmental control. We also plan to test against viruses, especially SARS-CoV-2, for viral control so if it works, we will focus on that, as well,” Robles told Laboratory Equipment.

With a Ph.D. in poultry science and an undergraduate class called Safety and Sanitation in the Hospitality Industry, Sujata Sirsat comes at the collaborative research from a different angle. She’s looking to stop mass product recalls, federal warnings, hospitalizations, and the death of an estimated 260 people annually due to listeriosis.

As reported in the Journal of Environmental Chemical Engineering, cobalt-doped titanium-dioxide (CoO-TiO2) stops the reproduction of listeria monocytogenes in both light and dark conditions. This effect could lead to bacterial control in food products that are not only sealed but also protected from light, such as tetra packs, cans and dark glass or plastic bottles.

Titanium-dioxide (TiO2) has long been an effective catalyst in the chemical industry with numerous applications but, since ultraviolet light is needed to activate it, there are limitations. Meanwhile, TiO2 is often used in the food industry as an additive or whitening agent for sauces and dressings, and is already considered safe by the FDA. It's also used in sunscreen for its protective effects against UV/UVB rays.

“UV light sources are in short supply in sunlight and producing it is expensive and a health hazard (e.g. carcinogen), so we set out to find a solution. Making it effective under natural light conditions is significant, and free,” Robles explained.

For the study, Robles and Sirsat doped TiO2 with various elements, looking for one that would result in a reduction of listeria monocytogenes. Typically, the most successful doping is done with precious metals (Au, Pt, Pd, etc.) that are expensive, but the researchers wanted to test with more affordable alternatives. Cobalt (Co) was among the less expensive elements—and it turned out to be very effective.

After 24 hours, listeria monocytogenes increased in the control sample approximately 340 percent. However, in samples treated with CoO-TiO2, the researchers recorded a reduction of bacteria by 80 to 90 percent after the 24-hour period. Further, and perhaps most importantly, the researchers showed Co sponsors TiO2 activity under sunlight, fluorescent light (domestic lightbulbs) and “dark” conditions, such as sealed containers or a refrigerator. This is a critical aspect of the study since, typically, TiO2 is active under UV light only, limiting or minimizing its activity when exposed to sunlight that contains 5 percent UV or less. To compound the problem, listeria monocytogenes has the ability to survive and grow at 41 F—the temperature of a refrigerator.

“Developing methodologies to promote activity of TiO2 under sunlight is a huge technological impact because we can take advantage of a very wide portion of the sunlight spectra from the infrared to the UV,” said Robles.

Further research on the topic will send Sirsat and Robles back to different paths.

Sirsat is interested in CoO-TiO2 manufactured directly into food packaging or added to food products as a way to potentially reduce the risk of large listeria outbreaks in food processing environments. Robles will apply the findings toward renewable energy, where he and his team are already in the process of publishing a major manuscript involving CoO-TiO2 material that “may be considered a world record in terms of hydrogen/clean and renewable energy production.”

In response to the current climate, Robles is also going to test the CoO-TiO2 material against viruses. He has agreements with colleagues in the environmental engineering fields to start working with surrogates that mimic the behavior of SARS-CoV-2. If the material works using these surrogates, Robles said he will contact a national laboratory to secure samples of actual SARS-CoV-2 for further testing.

“The possibilities are tremendous,” said Robles, who has been studying the effects of titanium-dioxide for nearly 15 years.