Application of atmospheric cold plasma, ultraviolet radiation, or natural antimicrobials for control of foodborne pathogenic and spoilage microorganisms

Non-thermal processing technologies have been given considerable attention in recent years due to their promising potential of inactivating spoilage and pathogenic microbes without compromising the quality, nutritional and sensory attributes of foods. Furthermore, the application of these technologies that utilize ambient temperature and preclude the addition of synthetic antimicrobials to achieve food preservation, addresses consumers demand for food products that are safe, healthy, nutritious, and devoid of synthetic preservatives. However, research to evaluate the efficiency of these non-thermal technologies against bacteria and mold species, and natural microflora, and their effectiveness against pathogenic bacteria in the robust long-term-survival (LTS) phase of their life cycle, is warranted. Furthermore, research on the extent of sub-lethal injury among survivors, and the efficiency of the thin agar layer (TAL) recovery method for recovering sub-lethally injured cells subjected to these technologies is important for ensuring food safety. In this regard, in these studies, the efficiency of three novel non-thermal technologies, namely, atmospheric cold plasma (ACP), Ultraviolet radiation (UV) and natural antimicrobials were evaluated for inactivation of Shiga-toxin producing Escherichia coli, Salmonella enterica, Listeria monocytogenes, natural microflora, or molds in model systems and in raw and ready-to-eat food products. In the ACP experiments, inoculated or non-inoculated portions (10 g) of tempered wheat grains were exposed to ACP (44 kV or 80 kV) dielectric barrier discharge. Additionally, the influence of the LTS state on the tolerance of E. coli O121 and Salmonella Typhimurium to ACP (80 kV), and the extent of sub-lethal injury in pathogen survivors in phosphate buffered saline (PBS) and on wheat grains were evaluated. The ACP (44 kV) was effective in reducing the populations of microorganisms (pathogenic and natural microflora) on the surface of wheat grains and substantial sub-lethal injury occurred among pathogen survivors. The LTS phase of E. coli O121 and Salmonella Typhimurium exhibited higher tolerance to ACP (80 kV) than stationary phase cells in PBS. However, on wheat grains there were no significant differences in log10 reductions of stationary phase and LTS phase. There was no substantial sub-lethal injury among stationary and LTS phase survivors. In the UV radiation (70 µW/cm2 or 1800 µW/cm2) experiment, we demonstrated that the TAL method is an effective method for the recovery of UV- induced sub-lethally injured cells and that TAL method is comparable to conventional methods of recovery. Lastly, in the natural antimicrobial experiment, CytoGuard® CDP Ultra and Inhibit violet were the most effective natural antimicrobials tested for strongly inhibiting growth of Penicillium species in shredded cheddar cheese; however, higher concentrations of these antimicrobials are required for significant growth inhibition of Aspergillus species. This research has demonstrated that the three non-thermal technologies evaluated are effective for microbial control on raw and ready-to-eat food products.