Purpose: This study aimed to investigate the impact of pressure and meat spoilage microbiota, with or without antimicrobials, on survival of Listeria after refrigerated storage.
Methods: Ham was inoculated with a five-strain cocktail of L. monocytogenes, alone or together with a cocktail of spoilage organisms (Leuconostoc spp., Lactobacillus sakei, Carnobacterium maltaromaticum, and Brochothrix thermosphacta). Products were treated at 500 MPa at 5°C for one or three minutes, with or without nisin or rosemary extract. Differential enumeration of cells was done after pressure treatment and after four weeks of refrigerated storage. Experiments were performed in triplicate.
Results: Treatment of Listeria for one or three minutes reduced counts by 1.05±0.39 and 2.08±0.33 log (CFU/g), respectively; inactivation of spoilage microbiota was comparable. Counts of Listeria increased by three and one log CFU/g during refrigerated storage after one or three minutes of treatment, respectively. The presence of spoilage microbiota did not influence inactivation of Listeria but prevented growth of Listeria after refrigerated storage. The addition of rosemary extract did not influence inactivation of Listeria or the spoilage microbiota, or growth of microorganisms during storage. The combination of nisin with pressure treatment for three minutes reduced counts of Listeria and spoilage microbiota by greater than five log CFU/g; after four weeks of storage counts were below the detection limit.
Significance: In conclusion, pressure application alone did not eliminate Listeria or spoilage microbiota on RTE ham; however, survival of spoilage organisms prevented growth of Listeria on pressure treated ham. Overall, this research furthers our understanding of the impact of pressure on lethality of spoilage organisms and Listeria.