title: Acid adaptation does not promote survival or growth of Listeria monocytogenes on fresh beef following acid and nonacid decontamination treatments.
abstract: The objective of this study was to evaluate the survival and growth of acid-adapted and nonadapted Listeria monocytogenes inoculated onto fresh beef subsequently treated with acid or nonacid solutions. Beef slices (2.5 by 5 by 1 cm) from top rounds were inoculated with acid-adapted or nonadapted L. monocytogenes (4.6 to 5.0 log CFU/cm2) and either left untreated (control) or dipped for 30 s in water at 55 degrees C, water at 75 degrees C, 2% lactic acid at 55 degrees C, or 2% acetic acid at 55 degrees C. The beef slices were vacuum packaged and stored at 4 or 10 degrees C and were analyzed after 0, 7, 14, 21, and 28 days of storage. Dipping in 75 degrees C water, lactic acid, and acetic acid resulted in immediate pathogen reductions of 1.4 to 2.0, 1.8 to 2.6, and 1.4 to 2.4 log CFU/cm2, respectively. After storage at 10 degrees C for 28 days, populations of L. monocytogenes on meat treated with 55 degrees C water increased by ca. 1.6 to 1.8 log CFU/cm2. The pathogen remained at low population levels (1.6 to 2.8 log CFU/cm2) on acid-treated meat, whereas populations on meat treated with 75 degrees C water increased rapidly, reaching levels of 3.6 to 4.6 log CFU/cm2 by day 14. During storage at 4 degrees C, there was no growth of the pathogen for at least 21 days in samples treated with 55 and 75 degrees C water, and periods of no growth were longer for acid-treated samples. There were no differences between acid-adapted and nonadapted organisms across treatments with respect to survival or growth. In conclusion, the dipping of meat inoculated with L. monocytogenes into acid solutions reduced and then inhibited the growth of the pathogen during storage at 4 and 10 degrees C, while dipping in hot water allowed growth despite initial reductions in pathogen contamination. The results of this study indicate a residual activity of acid-based decontamination treatments compared with water-based treatments for refrigerated (4 degrees C) or temperature-abused (10 degrees C) lean beef tissue in vacuum packages, and these results also indicate that this activity may not be counteracted by prior acid adaptation of L. monocytogenes.
authors.affiliation: Department of Animal Sciences, Colorado State University, Fort Collins, Colorado 80523-1171, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Ikeda
authors.forename: J
authors.initials: J
authors.lastname: Samelis
authors.forename: P A
authors.initials: PA
authors.lastname: Kendall
authors.forename: G C
authors.initials: GC
authors.lastname: Smith
authors.forename: J N
authors.initials: JN
authors.lastname: Sofos
mesh_terms: D019342:Acetic Acid / Q000494:pharmacology; D000222:Adaptation, Physiological; D000818:Animals; D002417:Cattle; D015169:Colony Count, Microbial; D005511:Food Handling / Q000379:methods*; D005516:Food Microbiology; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000494:pharmacology; D008089:Listeria monocytogenes / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D008460:Meat / Q000382:microbiology*; D013696:Temperature; D013997:Time Factors; D014618:Vacuum
chemical_list: D019344:Lactic Acid; D019342:Acetic Acid