Original article Effects of heat-processing regime, pH, water activity and their interactions on the behaviour of Listeria monocytogenes in ground pork. Modelling the boundary of the growth/no-growth areas as a function of pH, water activity and temperature Ve ´ronique Zuliani, 1 * Isabelle Lebert, 2 Pascal Garry, 1 Jean-Luc Vendeuvre, 1 Jean-Christophe Augustin 3 & Andre ´ Lebert 2 1 Centre Technique de la Salaison, de la Charcuterie et des Conserves de Viandes, 7 avenue du Ge´ne´ral de Gaulle, 94704 Maisons-Alfort Cedex, France 2 Unite´ Qualite´ des Produits Animaux, Institut National de la Recherche Agronomique, 63122 Saint-Gene`s Champanelle, France 3 Ecole Nationale Ve´te´rinaire d’Alfort, 7 avenue du Ge´ne´ral de Gaulle, 94704 Maisons-Alfort Cedex, France (Received 29 July 2005; Accepted in revised form 3 January 2006) Summary The influence of four heat-processing regimes and a storage phase on the behaviour of Listeria monocytogenes in ground pork was studied. The effects of pH and water activity (a w ) were also tested. During the heat process phase, a w , the heat-processing regime and its interactions with pH or a w , had a significant effect on the behaviour of L. monocytogenes. During the storage phase, all parameters tested and their interactions had significant effects. Nevertheless, the area in which the growth of L. monocytogenes was observed at the end of the experiment was not influenced by the heat-processing regime tested. On the contrary, pH, a w and their interactions had significant effects on Listeria behaviour. The boundary of the growth area delimited by environmental conditions where growth was higher than 1.0 Log CFU g )1 from those where growth was lower than this limit was correctly predicted by Augustin’s model. Keywords Augustin’s model, a w , growth/no-growth areas, heat-processing regime, Listeria monocytogenes, pH, pork meat. Introduction Bacterial food diseases frequently occur in developed countries with significant health and economic conse- quences. In 1999, 660 clusters were reported in France (Haeghebaert et al., 2002). Most of these diseases involved Salmonella, Staphylococcus aureus or Clostrid- ium perfringens. Other bacteria, such as Listeria mono- cytogenes, were involved as well (Buisson & Teysou, 2002). This bacteria is problematic because of its ability to grow over a wide range of temperatures, pH and water activity (a w ) values (Augustin, 1999), enabling it to survive in many foods. Listeria monocytogenes has often been involved in meat disease outbreaks: in France in 1992, 279 people became ill after consumption of pork tongue in aspic; a year later, potted minced pork was responsible for thirty-nine cases. In 1999 and 2000, potted minced pork and pork tongue in aspic were once again involved in listeriosis outbreaks in France (Folio, 2003). In 2002, a sausage mixture was incriminated in the last French outbreak because of the consumption of delicatessen products (The´venot et al., 2005). During the process of delicatessen products, physic- ochemical properties of the meat are modified: pH is decreasing because of the use of starter culture or addition of organic acid salt in the brine and water activity (a w ) is decreasing because of the addition of salts or water evaporation during drying (Durand, 1999). Temperature is also modified; indeed, it first increases during the heat process phase and then decreases during the storage at refrigeration temperature. In this study, the effects of pH, a w and heat-processing regime on the behaviour of L. monocytogenes inoculated in ground pork were studied during the heat process phase and the storage phase at 20 °C. Our aim was to determine the parameters and their interactions that had an influence on the evolution of contamination during a process composed of formulation, a mild heat treatment and a storage phase. We also studied the boundary *Correspondent: Fax: (33) 01 43 76 07 20; e-mail: vzuliani@ctsccv.fr International Journal of Food Science and Technology 2006, 41, 1197–1206 1197 doi:10.1111/j.1365-2621.2006.01185.x Ó 2006 Institute of Food Science and Technology Trust Fund