Postpackage Pasteurization of Ready-to-Eat Deli Meats by Submersion Heating for Reduction of Listeria monocytogenes

Abstract

A mixed cocktail of four strains of Listeria monocytogenes was resuspended in product purge and added to a variety of ready-to-eat (RTE) meat products, including turkey, ham, and roast beef. All products were vacuum sealed in shrink-wrap packaging bags, massaged to ensure inoculum distribution, and processed by submersion heating in a precision-controlled steam-injected water bath. Products were run in pairs at various time-temperature combinations in either duplicate or triplicate replications. On various L. monocytogenes-inoculated RTE deli meats, we were able to achieve 2- to 4-log cycle reductions when processed at 195 degrees F (90.6 degrees C), 200 degrees F (93.3 degrees C), or 205 degrees F (96.1 degrees C) when heated from 2 to 10 min. High-level inoculation with L. monocytogenes (approximately 10(7) CFU/ml) ensured that cells infiltrated the least processed surface areas, such as surface cuts, folds, grooves, and skin. D- and z-value determinations were made for the Listeria cocktail resuspended in product purge of each of the three meat categories. However, reduction of L. monocytogenes in product challenge studies showed much less reduction than was observed during the decimal reduction assays and was attributed to a combination of surface phenomena, including surface imperfections, that may shield bacteria from the heat and the migration of chilled purge to the product surface. The current data indicate that minimal heating regimens of 2 min at 195 to 205 degrees F can readily provide 2-log reductions in most RTE deli meats we processed and suggest that this process may be an effective microbial intervention against L. monocytogenes on RTE deli-style meats.

Effectiveness of commercial household steam cleaning systems in reducing the populations of Listeria monocytogenes and spoilage bacteria on inoculated pork skin surfaces

“…These inconsistencies may be attributed to the wrinkles and folds naturally present on the pork skins which might have provided protection to the inoculated bacteria from the steam treatment. Similar results have been reported by Muriana, Quimby, Davidson, and Grooms (2002) in the inactivation of L. monocytogenes on ready-to-eat deli meat subjected to post-package pasteurization by submersion heating. It was observed that when the deli meat was inoculated with 10 7 CFU=ml of L. monocytogenes, a relatively lower level of reduction was obtained at 205 F ð96:1 CÞ compared with the levels of reduction obtained at 195 F ð90:6 CÞ or 200 F ð93:3 CÞ (Muriana et al, 2002).…”

“…Similar results have been reported by Muriana, Quimby, Davidson, and Grooms (2002) in the inactivation of L. monocytogenes on ready-to-eat deli meat subjected to post-package pasteurization by submersion heating. It was observed that when the deli meat was inoculated with 10 7 CFU=ml of L. monocytogenes, a relatively lower level of reduction was obtained at 205 F ð96:1 CÞ compared with the levels of reduction obtained at 195 F ð90:6 CÞ or 200 F ð93:3 CÞ (Muriana et al, 2002). The authors attributed such inconsistencies to the imperfections of the product surfaces such as cuts, folds, deep grooves, wrinkles, or tears present on the surface of the deli meat (Muriana et al, 2002).…”

Freezing effects on survival ofListeria monocytogenes in artificially contaminated cold fresh-salmon

“…Several researchers have studied the contamination of meat products by Listeria monocytogenes as well as the agents suppressing such contamination, such as the addition of biopreservatives (Nilsson et al, 1997;Nufer et al, 2007), the use of high hydrostatic pressure (Murano et al, 1999), pulsed light systems (Elmnasser et al, 2007) and pasteurisation (Muriana et al, 2002;Juncher et al, 2000). It was concluded that preservation processes which are expected to limit microbial activity do not have a strong effect on meat quality.…”

Quantitative Evaluation of Thermal Inactivation Kinetics of Free-Floating Versus Surface-Attached Listeria innocua Cells

“…Next to these genetical/phenotypical hypotheses, several technological aspects/hypotheses have been focused upon in recent publications for explaining the observed phenomenon (i.e., increased microbial heat resistance on the product surface) and are formulated as follows: (1) migration of cold purge from a chilled product interior to the product surface resulting in a decrease in the processed surface temperature (Muriana et al 2002), (2) inactivation kinetics originating from a cocktail of microbes, which can substantially affect the observed microbial inactivation kinetics of the targeting organism (Avens et al 2002;Muriana et al 2002), (3) some food components (e.g., fat) having a protective effect on microbes (Murphy et al 2000;Doyle et al 2001), (4) freshly contaminating bacteria migrating into the skin of the product resulting in experiencing lower temperatures than the bacteria remaining on the product surface (Houben and Eckenhausen 2006).…”