Food-contact surface coating to help prevent contamination

Researchers at Texas A&M University have created a coating that can be applied to food-contact surfaces like conveyor belts, rollers and collection buckets, to prevent contamination by microorganisms. In addition to being germicidal, the coating is designed to be extremely water-repellent. Researchers believe that without water, bacteria cannot stick or multiply on surfaces, thereby curbing contamination from one piece of produce to another. Results from the study were published in the February issue of the journal ACS Applied Materials & Interfaces.

“In our study, we show that our new dual-function coating — one that can both repel and kill bacteria — can greatly mitigate bacterial spread, averting cross-contamination,” said Mustafa Akbulut, associate professor in the Artie McFerrin Department of Chemical Engineering.

Foodborne illness can be caused by a range of pathogens that include multiple strains of viruses and bacteria. To remedy any infection after harvest, fresh produce may be washed then sterilised in antimicrobials. However, bacteria can still hide in hard-to-reach places on the skins of fruits and vegetables. If the bacteria is large enough, it can also form protective sheaths, called biofilms, that further protect them from the action of sanitisers.

Contaminated produce items can spread the pathogens directly, by touching other food items, or indirectly, via food-contact surfaces. There are several ways to prevent indirect transmission, ranging from antimicrobial surface coatings to antifouling polymer surfaces that act like springs to push bacteria away. However, researchers believe these approaches, while efficient at first, can lose their effects over time for a variety of reasons.

The researchers therefore created an antimicrobial surface coating that was hydrophobic, which is designed to help the food-contact surface retain its germicidal action much longer.

“Most bacteria can only survive in an aqueous environment. If surfaces are super-hydrophobic, then water, and along with it most of the bacteria, will be repelled away. With fewer bacteria around, less germicides are used up, increasing the overall lifetime of the coating,” Akbulut said.

Schematic showing Dr Mustafa Akbulut’s dual-function coating that is both superhydrophobic and antimicrobial. Image credit: Texas A&M University College of Engineering.

To make the dual-function coating, researchers started with an aluminium sheet, a metal commonly used in the food industry for contact surfaces. Onto the surface of the metal, researchers chemically attached a thin layer of silica using high heat. With this layer as a substrate, researchers then added a mixture of silica and a naturally occurring germicidal protein found in tears and egg white called lysozyme.

Together, the silica-aluminium layer bound to the silica-lysozyme layer made a coating that had a rough texture when viewed at microscopic scales. The researchers noted that this submicroscopic roughness, or the tiny bumps and crevices on the coating, is key to superhydrophobicity.

When the superhydrophobic, lysozyme-infused coating was ready, the researchers tested if it was effective at curbing the growth of two strains of disease-causing bacteria — Salmonella typhimurium and Listeria innocua. Researchers discovered that the number of bacteria on these surfaces was 99.99% less than that on bare surfaces.

Despite the high efficacy of the coating in preventing bacterial spread, researchers said that more investigation is needed to determine if the coating works equally well for mitigating viral cross-contamination. Although longer lasting than other coatings, researchers noted that their coating would need to be reapplied after a certain amount of use. As a next step, the researchers are working on developing more permanent, dual-functionality coating.

“Our goal is to create smart surfaces that can avert any kind of pathogen from attaching and multiplying. In this regard, we have developed surface coatings that can prevent bacteria from collecting on surfaces, which is one of the major reasons for cross-contamination. We are now working with researchers in agriculture to take our invention from bench to practice,” Akbulut said.

Top image credit: ©stock.adobe.com/au/bibiphoto