title: Effects of lactic acid on the growth characteristics of Listeria monocytogenes on cooked ham surfaces.
abstract: The surfaces of ready-to-eat meats are susceptible to postprocessing contamination by Listeria monocytogenes. This study examined and modeled the growth characteristics of L. monocytogenes on cooked ham treated with lactic acid solutions (LA). Cooked ham was inoculated  with L. monocytogenes (ca. 10(3) CFU/g), immersed in 0, 0.5, 0.75, 1.0, 1.25, 1.5, and 2.0% LA for 30 min, vacuum packaged, and stored at 4, 8, 12, and 16°C. LA immersion resulted in <0.7 log CFU/g immediate reduction of L. monocytogenes on ham surfaces, indicating  the immersion alone was not sufficient for reducing L. monocytogenes. During storage, no growth of L. monocytogenes occurred on ham treated with 1.5% LA at 4 and 8°C and with 2% LA at all storage temperatures. LA treatments extended the lag-phase duration (LPD) of L. monocytogenes  and reduced the growth rate (GR) from 0.21 log CFU/day in untreated ham to 0.13 to 0.06 log CFU/day on ham treated with 0.5 to 1.25% LA at 4°C, whereas the GR was reduced from 0.57 log CFU/day to 0.40 to 0.12 log CFU/day at 8°C. A significant extension of the LPD and reduction of the  GR of L. monocytogenes occurred on ham treated with >1.25% LA. The LPD and GR as a function of LA concentration and storage temperature can be satisfactorily described by a polynomial or expanded square-root model. Results from this study indicate that immersion treatments with >1.5%  LA for 30 min may be used to control the growth of L. monocytogenes on cooked meat, and the models would be useful for selecting LA immersion treatments for meat products to achieve desired product safety.
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, Residue Chemistry and Predictive Microbiology Research Unit, 600 East Mermaid Lane, Wyndmoor, PA 19038, USA. andy.hwang@ars.usda.gov
authors.forename: Cheng-An
authors.initials: CA
authors.lastname: Hwang
authors.forename: Lihan
authors.initials: L
authors.lastname: Huang
authors.forename: Shiowshuh
authors.initials: S
authors.lastname: Sheen
authors.forename: Vijay
authors.initials: V
authors.lastname: Juneja
mesh_terms: D000818:Animals; D000891:Anti-Infective Agents, Local / Q000494:pharmacology*; D019540:Area Under Curve; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D004305:Dose-Response Relationship, Drug; D005511:Food Handling / Q000379:methods; D005519:Food Preservation / Q000379:methods*; D006801:Humans; D019344:Lactic Acid / Q000494:pharmacology*; D008089:Listeria monocytogenes / Q000187:drug effects* / Q000254:growth & development*; D008460:Meat / Q000382:microbiology*; D013552:Swine; D013696:Temperature
chemical_list: D000891:Anti-Infective Agents, Local; D019344:Lactic Acid