title: Impact of nitrite on detection of Listeria monocytogenes in selected ready-to-eat (RTE) meat and seafood products.
abstract: The impact of sodium nitrite (NaNO2) on detection and recovery of Listeria monocytogenes from select ready-to-eat (RTE) foods including smoked salmon, smoked ham, beef frankfurters, and beef bologna was assessed. Nitrite-containing (NC; 100 to 200 ppm NaNO2) or nitrite-free (NF) foods were inoculated with a 5-strain cocktail of L. monocytogenes by immersion into Butterfield's buffer solution containing 5.4 to 7.4 x 10(3) L. monocytogenes per milliliter. Inoculated products were vacuum-packaged and stored at 5 degrees C. A weekly comparative analysis was performed for presence of L. monocytogenes using 5 detection methods on products held at 5 degrees C for up to 8 wk. L. monocytogenes initially present at <100 CFU/g during the first 2 wk of storage increased throughout the study, attaining final populations of approximately 1 x 10(4) to 1 x 10(5) CFU/g. Lactic acid bacteria predominated throughout the study in all products. Exposure to NaNO2 (100 to 200 ppm) resulted in 83% to 99% injury to the L. monocytogenes strains tested. The genetic-based BAX System (DuPont Qualicon, Wilmington, Del., U.S.A.) and modified USDA/FSIS methods detected 98% to 100% of Listeria-positive food samples and were consistently superior to and significantly different (P < 0.05) from conventional cultural methods in recovering Listeria from NC samples. Data show that nitrite-induced injury adversely affects detection and recovery of L. monocytogenes from NC food, confirming earlier findings that nitrite-induced injury masks L. monocytogenes detection in NC RTE food products. Nitrite-injured Listeria can subsequently repair upon nitrite depletion and grow to high levels over extended refrigerated storage.
authors.affiliation: Dept. of Nutrition, Univ. of Massachusetts-Amherst, 100 Holdsworth Way, Amherst, MA 01003, USA. dgn@nutrition.umass.edu
authors.forename: D G
authors.initials: DG
authors.lastname: Nyachuba
authors.forename: C W
authors.initials: CW
authors.lastname: Donnelly
authors.forename: A B
authors.initials: AB
authors.lastname: Howard
mesh_terms: D000818:Animals; D002417:Cattle; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D005396:Fish Products / Q000382:microbiology*; D018857:Food Packaging / Q000379:methods; D005519:Food Preservation / Q000379:methods*; D005520:Food Preservatives / Q000494:pharmacology*; D006801:Humans; D007778:Lactobacillus / Q000254:growth & development; D008089:Listeria monocytogenes / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification; D008461:Meat Products / Q000382:microbiology*; D012474:Salmon; D017747:Seafood / Q000382:microbiology; D012977:Sodium Nitrite / Q000494:pharmacology*; D013552:Swine; D013997:Time Factors; D014618:Vacuum
chemical_list: D005520:Food Preservatives; D012977:Sodium Nitrite