Changes in the ability of Listeria monocytogenes to resist thermal treatment and simulated gastric condition after exposure to sequential stresses in minced meat.

ABSTRACT

In this study, Listeria monocytogenes from minced pork was evaluated for changes in resistance to thermal treatment and gastric fluid following environmental stresses during food processing. Bacteria were exposed to cold stress, followed by successive exposures to different stressors (lactic acid (LA), NaCl, or Nisin), followed by thermal treatments, and finally, their gastrointestinal tolerance was determined. Adaptation to NaCl stress reduced the tolerance of L. monocytogenes to subsequent LA and Nisin stress. Adaptation to LA stress increased bacterial survival in NaCl and Nisin-stressed environments. Bacteria adapted to Nisin stress showed no change in tolerance to subsequent stress conditions. In addition, treatment with NaCl and LA enhanced the thermal tolerance of L. monocytogenes, but treatment with Nisin decreased the thermal tolerance of the bacteria. Almost all of the sequential stresses reduced the effect of a single stress on bacterial thermal tolerance. The addition of LA and Nisin as a second step of stress reduced the tolerance of L. monocytogenes to gastric fluid, whereas the addition of NaCl enhanced its tolerance. The results of this study are expected to inform processing conditions and sequences for meat preservation and processing and reduce uncertainty in risk assessment of foodborne pathogens due to stress adaptation.