Controlling Campylobacter spp and Salmonella spp in poultry Processing using Cold Plasma and Natural Antimicrobials

This PhD scoped a framework of interventions for implementation at different stages of the post-slaughter poultry processing chain to control the contamination and cross-contamination risks of Salmonella and Campylobacter spp using a tailored range of cold plasma modes of delivery (liquid, gaseous, functionalised polymers) and natural compounds.
Plasma Functionalized Water (PFW) was generated using two different plasma systems. PFW functionalized using a microwaved Induced Plasma system (MidiPlex) showed that the plasma process parameters of plasma generation time, initial volume of water to be plasma treated, and contact time control its microbial reduction properties. This study successfully characterised and optimised the plasma process parameters to generate PFWs of increasing volumes up to 600 ml that can efficiently reduce poultry pathogens to undetectable levels. The chemical profile of these PFW showed the production of both Nitrate and Nitrite plasma reactive species, reduction of pH, and increase of the conductivity.
Other PFWs considered in this study were generated using the reactive species specificity plasma system (RSS) with two plasma discharges, namely Spark and Glow. The bactericidal effect of PFW-RSS differed with the plasma generation time, contact time, plasma discharge, and the target bacteria. The results revealed a high sensitivity for Salmonella spp and Campylobacter spp towards PFW-Spark. Different mechanisms of antimicrobial actions were observed to be involved for PFW; namely, intracellular oxidative stress, membrane damage, cell deformation, and destruction of metabolic activity. Live cell imaging and the consolidated videos of these bacteria while exposed to a diluted PFW for up to 1 hour confirmed the mechanisms of action assessed and the effect of specific plasma process parameters. The efficacy of PFW generated using the MidiPlex system demonstrated useful potential for controlling biofilms generated by Salmonella spp across different poultry processing conditions, and when attached to six commonly used food contact surfaces. Overall, the metabolic activity and the microbial load of cells forming the biofilms were reduced by up to 100% with 1 min washing with PFW. Biofilm analysis through AFM, SEM, and CLSM showed that PFW treatment led to significant damage to the structure of the biofilm, eruption of the cells generating these biofilms, and DNA denaturation. A sterilised chicken juice model was developed that mimicked the nutrient composition of fresh poultry meat without interfering with the natural microflora. This model was successfully used to optimize different delivery modes of cold plasma treatment and natural compounds to control the target pathogens. Aligned to the post-slaughter process stages for fresh poultry, the thermal stability of PFW generated using Midi-plex was considered and showed high bactericidal stability during and post-scalding. The combination of the two plasma treatment approaches using liquid and gaseous cold plasma applications, namely scalding and In-package DBD, showed efficiency for control of both Salmonella spp and Campylobacter spp over an extended storage time of 7 days at 4°C. The biological safety of implementing cold plasma treatments to the poultry process chain was assessed, and these treatments, whether applied separately or in combination, showed no short-term cytotoxic effect on a CHO-K1 cell line. Cold plasma treatment improved the microbial reduction potential of a chitosan edible coating. The intervention combination of misting with PFW, applying a plasma functionalized coating to the poultry with in-package DBD treatment, significantly improved the microbiological quality of fresh chicken meat, for both skin-on and skin-off chicken samples, compared to the untreated chicken meat. Overall, this thesis proposes safe and flexible approaches to implement CP into the current poultry processing chain easily.