Viability of Listeria monocytogenes on commercially-prepared hams surface treated with acidic calcium sulfate and lauric arginate and stored at 4 °C

We demonstrated the effectiveness of delivering an antimicrobial purge/fluid into shrink-wrap bags immediately prior to introducing the product and vacuum sealing, namely the "Sprayed Lethality In Container" (SLIC) intervention delivery method. The pathogen was Listeria monocytogenes, the antimicrobials were acidic calcium sulfate (ACS; calcium sulfate plus lactic acid; 1:1 or 1:2 in dH2O) and lauric arginate (LAE; Ethyl-N-dodecanoyl-L-arginate hydrochloride; 5% or 10% in dH2O), and the product was commercially prepared "table brown" ham (ca. 3 pounds each). Hams were surface inoculated with a five-strain cocktail of L. monocytogenes (ca. 7.0 log10 CFU per ham), added to shrink-wrap bags that already contained ACS or LAE, vacuum-sealed, and stored at 4 degrees C for 24 h. Pathogen levels decreased by 1.2, 1.6, 2.4, and 3.1 log10 CFU/ham and 0.7, 1.6, 2.2, and 2.6 log10 CFU/ham in samples treated with 2, 4, 6, and 8 mL of a 1:1 and 1:2 solution of ACS, respectively. In samples treated with 2, 4, 6, and 8 mL of a 5% solution of LAE, pathogen levels decreased by 3.3, 6.5, 5.6, and 6.5 log10 CFU/ham, whereas when treated with a 10% solution of LAE pathogen levels decreased ca. 6.5 log10 CFU/ham for all application volumes tested. The efficacy of ACS and LAE were further evaluated in shelf-life studies wherein hams were surface inoculated with either ca. 3.0 or 7.0 log10 CFU of L. monocytogenes, added to shrink-wrap bags that contained 0, 4, 6, or 8 mL of either a 1:2 solution of ACS or a 5% solution of LAE, vacuum-sealed, and stored at 4 degrees C for 60 days. For hams inoculated with 7.0 log10 CFU, L. monocytogenes levels decreased by ca.1.2, 1.5, and 2.0 log10 CFU/ham and 5.1, 5.4, and 5.5 log10 CFU/ham within 24 h at 4 degrees C in samples treated with 4, 6, and 8 mL of a 1:2 solution of ACS and a 5% solution of LAE, respectively, compared to control hams that were not treated with either antimicrobial. Thereafter, pathogen levels remained relatively unchanged (+/-1.0 log10 CFU/ham) after 60 days at 4 degrees C in hams treated with 4, 6, and 8 mL of a 1:2 solution of ACS and increased by ca. 2.0-5.0 log10 CFU/ham in samples treated with 4, 6, and 8 mL of a 5% solution of LAE. For hams inoculated with 3.0 log10 CFU, L. monocytogenes levels decreased by 1.3, 1.9, and 1.8 log10 CFU/ham within 24 h at 4 degrees C in samples treated with 4, 6, and 8 mL of a 1:2 solution of ACS, respectively, compared to control hams that were not treated. Likewise, levels of the pathogen were reduced to below the limit of detection (i.e., 1.48 log10 CFU/ham) in the presence of 4, 6, and 8 mL of a 5% solution of LAE within 24 h at 4 degrees C. After 60 days at 4 degrees C, pathogen levels remained relatively unchanged (+/-0.3 log10 CFU/ham) in hams treated with 4, 6, and 8 mL of a 1:2 solution of ACS. However, levels of L. monocytogenes increased by ca. 2.0 log10 CFU/ham in samples treated with 4 and 6 mL of a 5% LAE solution within 60 days but remained below the detection limit on samples treated with 8 mL of this antimicrobial. These data confirmed that application via SLIC of both ACS and LAE, at the concentrations and volumes used in this study, appreciably reduced levels of L. monocytogenes on the surface of hams within 24 h at 4 degrees C and showed potential for controlling outgrowth of the pathogen over 60 days of refrigerated storage.