Responses of pathogens on fresh beef and ready-to-eat meat products subjected to processing, preparation, and consumption associated stresses

Abstract

This research was undertaken to elucidate the responses of Escherichia coli O157:H7 and Salmonella spp. on fresh beef and Listeria monocytogenes on ready-to-eat (RTE) meat products exposed to stresses associated with processing, preparation and consumption. Initially, studies evaluated the use of decontamination interventions to reduce E. coli O157:H7 populations on beef tissue. In general, it appeared that pathogen reductions achieved with treatments combining two 5% lactic acid applications or at least one hot (82°C) and one 5% lactic acid application were greater than those achieved with treatments including one or more hot (82°C) application or a single 5% lactic acid application. In another study, the effect of chemicals included in a simulated spray-chilling process was evaluated on beef tissue inoculated with acid- or nonacid-habituated E. coli O157:H7. Previous acid-habituation of E. coli O157:H7 rendered the cells more resistant to the effects of spray-chilling, especially with acid; however, reductions achieved, irrespective of acid-habituation, followed the order spray-chilling with water = nonspray-chilling < spray-chilling with chemical solutions. In the third study, the effect of strain interaction on growth and acid tolerance response of E. coli O157:H7 inoculated in meat decontamination runoff fluids (washings) and on meat was evaluated. Results indicated that mixing and subsequent co-habitation of E. coli O157:H7 strains prior to inoculation of meat and washings did not affect their growth or acid tolerance. Acid-adaptation of E. coli O157:H7 on meat or washings at refrigeration temperatures may promote its resistance to subsequent interventions, especially acidic. The fourth study involved use of E. coli O157:H7 inocula of different histories to evaluate resistance responses during exposure to stresses simulating incomplete cooking and consumption. It was evident that heat and acid tolerance of the pathogen were influenced by inoculum history and more so by temperature of storage and transfer from anaerobic to aerobic conditions during storage. In the final study, survival of L. monocytogenes on ready-to-eat (RTE) pork frankfurters with antimicrobials as ingredients and/or dipping treatments was determined after exposure to a simulated gastric fluid. The combination of formulation of frankfurters with formulated with 0.25% sodium diacetate and dipping in 2.5% lactic acid appeared to increase the pathogen's acid tolerance. In general, the greater the growth of L. monocytogenes on frankfurters during storage, the higher the chance of survival in simulated gastric fluid.