Effectiveness and stability of plastic films coated with nisin for inhibition of Listeria monocytogenes

Plastic films were coated with a cellulose-based carrier solution containing nisin, a natural antimicrobial peptide with the potential to inhibit growth of food spoilage and pathogenic microorganisms such as Listeria monocytogenes. Five commercial plastic films with different chemical compositions and surface properties were compared in this study: low-density polyethylene, ethylene-vinyl acetate copolymer, and three types of ethylene-methacrylic acid copolymers: Surlyn 1601, Nucrel 0403, and Nucrel 0903. The films were coated with nisin at a concentration of 1000 IU/cm2. Nisin-coated films were stored at room temperature (21 degrees C) and at 4 degrees C and analyzed weekly for 12 weeks. Antimicrobial activity of the different nisin-coated films against a nisin indicator strain, Lactococcus lactis subsp. cremoris ATCC 14365, and against L. monocytogenes ATCC 19115 was assessed using an inhibition zone assay. Nisin incorporated into the films was recovered by a boiling and extraction procedure, and its activity was quantified using an agar well diffusion assay. Film type did not have any significant effect on the antimicrobial activity of the nisin-coated films (P < 0.05); all five film types had comparable inhibition zones on both assays. The films maintained stable activity for the duration of the study, both at room temperature and refrigeration. The results of this study demonstrate that commercially available packaging films can be coated with nisin and the resulting antimicrobial films can be conveniently stored at room temperature with no adverse effect on nisin activity.