Anti-Listeria activity by various modes of delivery of nisin in a broth system and release kinetics of nisin-containing food packaging

In order to identify conditions for efficient food preservation by nisin, the sensitivity of Listeria monocytogenes to this preservative was studied under the following three modes of delivery: (1) the instantaneous addition of nisin into broth medium to simulate the formulation of nisin in foods, (2) the slow delivery of nisin solution into broth medium using a pump to simulate the slow release of nisin from packaging materials to foods, and (3) a combination of the two delivery methods. We conclude that the antimicrobial effectiveness of nisin strongly depends on its mode of delivery. The instantaneous and slow methods for adding nisin inhibited L. monocytogenes , but over time of exposure, L. monocytogenes developed tolerance to nisin. Our data indicate that cells treated with instantaneously added nisin developed resistance to higher concentrations of nisin (200 IU/mL), compared to cells treated with slowly added nisin at the same total amount of the antimicrobial. Further studies indicated that nisin-tolerant cells recovered from treatments in which 200 IU/mL nisin was added instantaneously were likely to be mutants resistant to the bacteriocin. In contrast, nisin-tolerant cells recovered from treatments, when 200 IU/mL of the antimicrobial was added slowly to the cells developed only a temporary tolerance; these cells became nisin-sensitive after passage through nisin-free medium. Due to the development of nisin-resistant cells, excessive amounts of nisin in the model system did not further inhibit L. monocytogenes. These results signify that excess nisin in foods does not necessarily improve the efficiency of controlling L. monocytogenes. Our data suggest that the combination of packaging material containing nisin used in conjunction with nisin-containing foods will provide the most effective means of preventing L. monocytogenes growth.;This study also identified a major technical challenge in developing antimicrobial food packaging (AFP) research: a packaging material containing single polymers is limited to narrow ranges of active compound release rates. In order to overcome this research gap, a new approach that consists of using polymer blends and smart blend (based on the principle of chaotic advection) might be a promising approach in developing a new generation of antimicrobial food packaging.