Switchable Antimicrobial and Antifouling Coatings on Stainless-steel for Eliminating Cross-Contamination in Food Manufacturing

Abstract

Bacterial infections and the increased risk of antimicrobial resistance are paramount challenges, resulting in a severe threat to public health worldwide. According to the Centers for Disease Control and Prevention (CDC) surveillance report, pathogenic micro-organisms can cause up to millions of cases of foodborne sickness and deaths. Microbial contamination is a leading cause of foodborne illnesses that burden healthcare, food manufacturing and packaging, and water industries. In the food industries, cutting components, processing tables, conveyor belts, rollers, and floors are major surfaces that contribute to the transmission of bacterial pathogens from one material to another. This transmission usually occurs during post-harvest food processing, such as washing, grading, cutting, and packaging. Developing surface modification, functionalization, and coating strategies that inhibit and prevent bacterial attachment, proliferation, and growth is the most critical step to handle this global challenge and recently has gathered increased attention. This project aims to reduce adhesion, survival, and cross-contamination of Escherichia coli and Listeria spp. in the food-processing industry by developing and applying antibacterial surfaces with electromagnetically switchable bacteria-killing and bacteria-releasing characters. Copolymerization of pyrrole and pyrrole-2-Carboxylic acid was carried out to generate a coating layer on the stainless-steel coupons. Quaternary Ammonium Salt functionalized diol, N-methyl-N-dodecyl-N, N-bis(2-hydroxyethyl) ammonium bromide (C12QAS) was then incorporated into the polypyrrole coatings. The physicochemical properties of the coatings were characterized. The bacteria-killing and bacteria-releasing ability of the coatings were determined against two bacterial species representatives of the species of interest, i.e., E. coli and Listeria innocua, to the food manufacturing industries. This project demonstrates that PPy-2-COOH coatings were successfully synthesized, and the C12QAS was immobilized on the coatings. The PPy-2-COOH coatings exhibited significantly superhydrophobic property, with the contact angle of 150.0º and surface energy of 40.11mN/m. The proposed antimicrobial coatings demonstrated their efficacy in inactivating foodborne pathogens E. coli and L. innocua. After 1-hour exposure, the antimicrobial coatings with the highest QAS concentration could inactivate 5 log CFU/cm2 of bacteria. Furthermore, the efficacy of the coatings in bacterial releasing was evaluated. By applying a 1-volt electric current on the stainless-steel coupons, the positively charged coatings can release the adhered bacteria from the stainless-steel surface by 2 log CFU/cm2 compared to the coupons without charging. Overall, the proposed antimicrobial coatings will address unmet needs in controlling pathogen persistence in growth niches. While the proposed research demonstrates the application of these smart coatings on stainless-steel, polypyrrole-based polymers adhere strongly to other materials (e.g., plastics, glass, metals), demonstrating the versatility of the proposed coating. Further, while our study focuses on efficacy against Listeria spp. and E. coli, the antimicrobial coatings are expected to perform well against other foodborne pathogens as well as food spoilage organisms. The outputs of this project therefore have significant potential for long-range improvement in and sustainability of NZ agriculture and food systems.