Synergistic activity between lauric arginate and carvacrol in reducing Salmonella in ground turkey.

In the present study, low concentrations of carvacrol (0.025 to 0.2%) and lauric arginate (LAE; 25 to 200 ppm) were tested at 4, 22, and 45°C in a broth model, and higher concentrations of carvacrol (0.1 to 5%) and LAE (200 to 5,000 ppm) were tested individually and in combination at 4°C in 3 different ground turkey samples (with 15, 7, and 1% fat content) for their effectiveness against a 3-strain mixture of Salmonella. A low concentration of 25 ppm of LAE or 0.025% carvacrol had no effect on Salmonella in a broth model, but their mixture showed a synergistic action by reducing 6 log cfu/mL Salmonella counts to a nondetectable level within 30 min of exposure. The US Food and Drug Administration-recommended 200 ppm of LAE was not sufficient for Salmonella reductions in ground turkey when applied internally. High concentrations of 2,000 to 5,000 ppm of LAE or 1 to 2% carvacrol were needed to reduce Salmonella counts by 2 to 5 log cfu/g in ground turkey by internal application. No specific relationship existed between fat content and LAE or carvacrol concentrations for Salmonella reductions. For example, 2,000 ppm of LAE could reduce Salmonella counts by 4 log cfu/g in 1% fat-containing turkey samples but very similar ~1.5 log cfu/g reductions in both 7 and 15% fat-containing ground turkey samples. For the total microbial load, about 2,000 ppm of LAE or 2% of carvacrol treatments were needed to achieve 2 to 3 log (P ≤ 0.05) cfu/g reductions in different turkey samples. A mixture of 1% carvacrol and 2,000 ppm of LAE exhibited a synergistic action in ground turkey containing 7% fat by reducing the Salmonella counts by 4 log cfu/g, which was not found with individual antimicrobial treatments.

Inhibition and inactivation of Salmonella typhimurium biofilms from polystyrene and stainless steel surfaces by essential oils and phenolic constituent carvacrol.

Persistence of Salmonella biofilms within food processing environments is an important source of Salmonella contamination in the food chain. In this study, essential oils of thyme and oregano and their antimicrobial phenolic constituent carvacrol were evaluated for their ability to inhibit biofilm formation and inactivate preformed Salmonella biofilms. A crystal violet staining assay and CFU measurements were utilized to quantify biofilm cell mass, with evaluating factors such as strain variation, essential oil type, their concentrations, exposure time, as well as biofilm formation surface. Of the three Salmonella strains, Salmonella Typhimurium ATCC 23564 and Salmonella Typhimurium ATCC 19585 produced stronger biofilms than Salmonella Typhimurium ATCC 14028. Biofilm formation by different Salmonella strains was 1.5- to 2-fold higher at 22°C than at 30 or 37°C. The presence of nonbiocidal concentrations of thyme oil, oregano oil, and phenolic carvacrol at 0.006 to 0.012% suppressed Salmonella spp. biofilm formation 2- to 4-fold, but could not completely eliminate biofilm formation. There was high correlation in terms of biofilm inactivation, as determined by the crystal violet-stained optical density (at a 562-nm wavelength) readings and the viable CFU counts. Reduction of biofilm cell mass was dependent on antimicrobial concentration. A minimum concentration of 0.05 to 0.1% of these antimicrobial agents was needed to reduce a 7-log CFU biofilm mass to a nondetectable level on both polystyrene and stainless steel surfaces within 1 h of exposure time.

Reduction of Listeria monocytogenes in queso fresco cheese by a combination of listericidal and listeriostatic GRAS antimicrobials.

Single and combined effects of three GRAS (generally recognized as safe) antimicrobials including, bacteriophage P100 (phage P100), lauric arginate (LAE), and potassium lactate-sodium diacetate mixture (PL-SD) were evaluated against Listeria monocytogenes cold growth in queso fresco cheese (QFC). The fate of phage P100 when exposed to LAE (200 ppm) or PL-SD (2.8% PL and 0.2% SD) was determined at 4°C and 30°C in a broth model. Phage P100 was found to be stable in the presence of these antimicrobial agents as plaque forming units (PFU) did not vary between control, LAE or PL-SD treatments. When 9 log CFU/ml of stationary phase cells of L. monocytogenes was exposed to these antimicrobials in tryptic soy broth, there was a 3 to 5 log CFU/ml reduction with phage P100 and a complete 9 log CFU/ml reduction with LAE but no measurable reduction with PL-SD after 24h at 4°C or 30°C. In QFC, the L. monocytogenes populations increased from the initial 3.5 log CFU/cm(2) to 7.7 log CFU/cm(2) in 28 days at 4°C. Treatment with 7.8 log PFU/cm(2) of phage P100 or 200 ppm of LAE showed strong listericidal effect initially by reducing L. monocytogenes counts by 2 to 3.5-4 log CFU/cm(2) while there was a subsequent regrowth of L. monocytogenes at 4°C. Treatment with PL-SD showed strong listeriostatic effect without decreasing L. monocytogenes counts but growth was prevented for 28 days at 4°C. Only the combined treatment of listericidal phage P100 or LAE with listeriostatic PL-SD reduced the initial L. monocytogenes counts by 2-4 log CFU/cm(2) and also kept the L. monocytogenes counts at that reduced level in QFC for 28 days at 4°C.