Development and evaluation of pullulan-based composite antimicrobial films (CAF) incorporated with nisin, thymol and lauric arginate to reduce foodborne pathogens associated with muscle foods

A novel composite antimicrobial film (CAF), made from a pullulan-based biopolymer and polyethylene (PE) was developed and evaluated for controlling pathogens associated with muscle foods. Initially, CAFs were developed by incorporating thymol (T), nisin (N) and/or lauric arginate (LAE) into the pullulan layer and layering it on top of PE. The antimicrobial activity of the resulting CAFs was evaluated against cocktails of Shiga toxin-producing E. coli (STEC), Salmonella spp., Listeria monocytogenes (L. monocytogenes) and Staphylococcus aureus (S. aureus) in disk diffusion assays (DDAs). CAFs containing N were ineffective, while those containing T were effective for inhibiting the pathogens in DDAs. However, CAFs made with them did not exhibit desirable physical and mechanical properties since solvents (HCl and ethanol, respectively) interfered with the binding of pullulan to PE. Conversely, CAFs made with 0.5, 1 and 2.5% LAE maintained proper physical and mechanical characteristics and inhibited the four bacterial pathogens in DDAs. Based on these preliminary results, cocktails consisting of approximately 8 log₁₀ CFU/ml of STEC, Salmonella, L. monocytogenes, or S. aureus were experimentally-inoculated onto raw beef, raw chicken breast, or ready-to-eat (RTE) turkey breast to obtain approximately 6.6 log₁₀ CFU/cm², aseptically transferred to CAFs containing 0.5, 1, or 2.5% LAE that were made into sachets/bags, vacuum packaged, sealed, and remaining microbial populations determined up to 28 days of refrigerated storage (4 °C). By day 28, CAFs containing 0.5, 1, and 2.5% LAE reduced: STEC by 1.13, 1.33 and 2.88 log₁₀ CFU/cm² respectively, on raw beef; Salmonella by 2.03, 2.12 and 3.01 log₁₀ CFU/cm² respectively, on raw chicken breast; L. monocytogenes by 1.12, 1.81 and 3.56 log₁₀ CFU/cm² respectively, on RTE turkey breast; and S. aureus by 0.68, 2.02 and 3.43 log₁₀ CFU/cm², respectively, on RTE turkey breast. CAFs may be of interest to the meat and poultry industry to control foodborne pathogens associated with these food products.