Multi-method approach indicates no presence of sub-lethally injured Listeria monocytogenes cells after mild heat treatment.
Application of mild inactivation treatments follows an increasing trend in the food industry and is often combined with sub-optimal intrinsic product conditions to ensure appropriate level of microbial safety. Listeria monocytogenes was subjected to mild heat treatment (20 min at 60 degrees C) and subsequently exposed to various mild preservation conditions based on increased NaCl concentration and decreased pH. Recovery and resuscitation of L. monocytogenes cells were studied using various methods. Using 12-fold Most Probable Number (MPN) method no difference in the amount of recovered cells under adverse conditions was noted between heat-treated and non-treated L. monocytogenes cells. Time-to-detection method using on-line OD measurements showed that heat-treated L. monocytogenes cells reached detection limit faster in acidified media and NaCl supplemented media in comparison with non-heated control cells. Flow cytometry (FCM) analysis using 5-6-carboxyfluorescein diacetate (cFDA) and propidium iodide (PI) staining showed presence of low numbers of viable cells. Overall, there was no indication of sub-lethal injury in L. monocytogenes cells after mild heat treatment.
Uyttendaele
Mieke
M
Laboratory of Food Microbiology and Food Preservation, Department of Food Safety and Food Quality, Ghent University, Coupure links 653, B-9000 Ghent, Belgium. mieke.uyttendaele@ugent.be
Rajkovic
Andreja
A
Van Houteghem
Nancy
N
Boon
Nico
N
Thas
Olivier
O
Debevere
Johan
J
Devlieghere
Frank
F
D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D005434:Flow Cytometry; D005511:Food Handling / Q000379:methods*; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods*; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008089:Listeria monocytogenes / Q000254:growth & development*; D013997:Time Factors