Cold plasma treatment of ready-to-eat ham: Influence of process conditions and storage on inactivation of Listeria innocua.

Ready-to-eat (RTE) deli meat has been linked to several Listeria monocytogenes associated recalls. Recent studies demonstrated the potential antimicrobial effects of atmospheric cold plasma treatment on various food surfaces including RTE meat products. However, the influence of intrinsic and extrinsic factors, determining the efficacy of cold plasma to reduce Listeria has not been reported. This study investigated the influence of rosemary extract, salt (% NaCl), and treatment temperature on the efficacy of plasma to reduce numbers of L. innocua on RTE ham. The effect of post-treatment storage on L. innocua inactivation was also investigated. When the cold plasma treatment temperature was 4 °C, we observed a significant reduction in L. innocua of 1.75 and 1.51 log CFU/cm2 on 1% and 3% NaCl ham surface without rosemary extract respectively, after 180 s treatment. At a treatment temperature of 23 °C, the L. innocua cells were reduced by 1.78 and 1.43 log CFU/cm2, respectively on these surfaces after 180 s. No significant effects of salt concentration and treatment temperature were observed on L. innocua inactivation during cold plasma treatment of ham. The post treatment storage at 4 °C for 6 h after 180 s of plasma treatment enhanced further reduction of L. innocua on 1% NaCl ham without rosemary. We also observed the increased concentration of malondialdehyde (MDA) equivalent lipid oxidation of plasma treated samples and was significantly higher (1.53 MDA mg/ kg ham) compared to untreated samples (0.92 MDA mg/kg ham). However, no significant differences in surface color parameters, L* and b* values were observed after plasma treatment, except a significant increase in a* values. The water content of plasma exposed samples decreased significantly for all treatment conditions whereas the water activity values were not changed significantly. In conclusion, the atmospheric cold plasma could be applied as a means for surface decontamination of RTE ham. However, the drying and oxidation of ham should be controlled in an open atmospheric plasma treatment condition.