Dual-Effect Coating

Dual-Action Coating Invented to Prevent Bacterial Cross-Contamination Researchers at Texas A&M University have developed a coating that can be applied to surfaces such as conveyor belts and collection bins. Fresh vegetables and fruits can become contaminated by microorganisms during their journey from the field to produce displays in stores. These products can then spoil other products, spread contamination further, and increase the number of food items that could cause illness. Researchers at Texas A&M University have developed a coating that can be applied to food-contact surfaces such as conveyor belts, rollers and collection bins to prevent cross-contamination between fresh produce. The research team designed their coating to be both antimicrobial and highly water-repellent. Researchers noted that without water, bacteria cannot adhere to or multiply on surfaces, thereby largely preventing contamination from transferring from one product to another. Mustafa Akbulut, Associate Professor in the Artie McFerrin Department of Chemical Engineering, stated: "Consuming contaminated raw food causes hundreds of people to become ill each year. For this reason, food contamination is not only a major health concern but can also be seen as a significant economic burden. In our work, we demonstrated that our new dual-functional coating, which can both remove and kill bacteria, can greatly reduce bacterial spread by preventing cross-contamination." The results of the study appear in the February issue of ACS Applied Materials & Interfaces. A number of pathogens containing various viruses and bacteria types can lead to foodborne illnesses. To prevent possible infection after harvest, fresh produce is typically washed and then sterilized with strong antimicrobials such as hydrogen peroxide or acetic acid. However, if bacteria succeed in surviving in hard-to-reach places on the skins of fruits and vegetables, they can continue to survive. Additionally, if the bacterial count is sufficiently high, they can form protective shells called biofilms that shield them from the effects of disinfectants. Contaminated products can spread pathogens directly by contact with other food items or indirectly through food-contact surfaces. Currently, there are a few ways to prevent indirect contamination, from antimicrobial surface coatings to fouling-resistant polymers that act like springs to remove bacteria. However, researchers say that while these approaches may be initially effective, they can lose their effectiveness over time for various reasons. To overcome the limitations of existing technologies, Akbulut and his team continued to create an antimicrobial surface coating that is also highly hydrophobic. They noted that the coating's water-repellent properties could help food-contact surfaces maintain their antiseptic effects for much longer. Akbulut said, "Most bacteria can only survive in aqueous environments." "If surfaces are superhydrophobic, then water and most bacteria with it will be removed. Because there are fewer bacteria around, less antimicrobial is needed, which also extends the coating's service life." Akbulut and his team started with an aluminum sheet, a metal commonly used for contact surfaces in the food industry, to create their dual-functional coatings. They chemically bonded a thin composite layer called silica to the metal's surface using high heat. Then, with this layer as a substrate, they added a mixture of silica and lysozyme, a naturally occurring antimicrobial protein found in egg white and tears, and a silica mixture. The silica-aluminum layer bonded to the silica-lysozyme layer created a coating with a rough texture when viewed at microscopic scales. Researchers noted that this microscopic roughness, or the small bumps and crevices in the coating, is the key to superhydrophobicity. Shuhao Liu, a graduate student in the College of Engineering and principal author of the study, stated: "In general, if you increase roughness, the hydrophobicity of a material increases, but there is a limit. If the coating is too rough, bacteria can once again hide behind crevices and become contaminated. Therefore, without compromising the coating's overall function, we modified the ratio of silica and lysozyme so that the roughness would provide the best possible hydrophobicity." After fine-tuning the superhydrophobic, lysozyme-grafted coating and having it ready, the researchers tested whether it was effective in preventing the growth of two disease-causing bacterial types, Salmonella typhimurium and Listeria innocua. In their examination, they found that the bacterial count on these surfaces was 99.99 percent lower than on bare surfaces. Despite the high effectiveness of their coating in preventing bacterial spread, researchers noted that further research would be needed to determine whether the coating works equally well in reducing viral cross-contamination. Although the coating has a longer service life than other coatings, researchers noted that the coating they developed also needs to be reapplied after certain use. For this reason, Akbulut and his team are continuing work to develop more durable, dual-functional coatings for the next step. Akbulut said, "Our goal is to create smart surfaces that can prevent any type of pathogen from adhering and multiplying." "In this context, we have developed surface coatings that can prevent bacteria from accumulating on surfaces, one of the most important causes of cross-contamination. Now we are working with researchers in agriculture to move our invention from the laboratory to practice." Reference: "Dual-Functional, Superhydrophobic Coatings with Bacterial Anticontact and Antimicrobial Characteristics" Written by: Shuhao Liu, Jeremy Zheng, Li Hao, Yagmur Yegin, Michael Bae, Beril Ulugun, Thomas Matthew Taylor, Ethan A. Scholar, Luis Cisneros-Zevallos, Jun Kyun Oh and Mustafa Akbulut, 5 February 2020, ACS Applied Materials & Interfaces. Other contributors to the research include Michael Bae and Ethan A. Scholar from the Texas A&M Department of Chemical Engineering; Jeremy Zheng and Beril Ulugün from the Texas A&M Department of Biomedical Engineering; Li Hao from Zhongkai Agricultural and Engineering University in China; Thomas Matthew Taylor, Luis Cisneros-Zevallos and Yagmur Yegin from the Texas A&M Department of Nutrition and Food Science; and Jun Kyun Oh from Dankook University in the Republic of Korea.

This work was supported by the Food Production Technology Program and the United States Department of Agriculture.

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