Listeria monocytogenes is difficult to control in food and processing environments due to its widespread nature and ability to survive in a range of adverse conditions, including low temperatures, pH, and high salt concentrations. The objective of this study was to evaluate the efficacy of Photohydroionization™ (PHI; RGF Environmental Group, Inc., Riviera, Beach, FL), a novel advanced oxidation technology, as a surface treatment to control L. monocytogenes on food-contact surfaces, sliced American cheese, and ready-to-eat (RTE) turkey. A five-strain cocktail of L. monocytogenes was used to inoculate sample surfaces. Food-contact surfaces were exposed to ultraviolet and other oxidative gases produced by the PHI system for 10, 20, 30, 45, 60, and 120 s and 5, 10, and 15 min; cheese and turkey samples were treated for 30, 60, and 120 s and 5 min. For each matrix at each time point, seven samples were treated and enumerated by plating appropriate dilutions onto modified oxford medium and thin-agar-layer modified oxford medium. Results showed reductions (p<0.05) in L. monocytogenes: 4.37 log colony-forming units (CFU)/coupon on stainless steel after 15-min treatment. A 1.39 and 1.63 log CFU/sample after 120 s and 2.16 and 2.52 log CFU/sample after 5 min were seen on American cheese and ready-to-eat turkey, respectively. Lipid oxidation analyses performed on cheese and turkey samples indicated that PHI treatment did not affect (p>0.05) thiobarbituric acid-reactive substances values. This study demonstrates the efficacy of PHI treatment to reduce L. monocytogenes on stainless steel and RTE foods and may serve as a processing intervention to ensure safe production of food.
Commercially processed foods become contaminated with Listeria monocytogenes in post-processing environments where favorable conditions help the bacteria thrive. The US Food and Drug Administration has approved Lauric arginate (LAE) as generally recognized as safe (GRAS) for certain food applications. This study evaluated the efficacy of Mirenat-N (LAE dissolved in food-grade propylene glycol) against L. monocytogenes on food contact surfaces. A three-strain cocktail of L. monocytogenes was used to inoculate 24 polished stainless steel coupons with three treatments, 100 ppm and 200 ppm solutions of LAE and water (control); two sub-treatments of high (6 log CFU/ml) and low (4 log CFU/ml) inoculum levels; and two contact times of 5 and 15 min. Attached bacteria were dislodged by vortexing coupons for 1 min with 20 g of 3-mm solid glass beads in 10 ml of 0.1% peptone diluent, and bacterial populations were calculated by plating onto modified oxford medium (MOX) and thin agar layer MOX (TALMOX). The 100 ppm treatment showed average reductions of 1.38 and 2.57 log CFU/coupon at the low inoculum level and 0.37 and 0.62 log CFU/coupon at high inoculum levels, after 5 and 15 min exposure, respectively. For 200 ppm at the high inoculum level, 1.23 and 1.88 log CFU/coupon reductions were seen for 5 and 15 min, respectively; the low inoculum level at 5 and 15 min exposure showed reductions of ≤1.5 log CFU/coupon. The 100 ppm LAE treatment was more effective at low inoculum levels for 5 and 15 min contact times and may be used to control low levels of contamination of L. monocytogenes on food contact surfaces.
Floor drains in processing environments harbor Listeria spp. due to continuous presence of humidity and organic substrates. Cleaning and washing activities in food-processing facilities can translocate the bacterial cells from the drain to the surrounding environment, thus contaminating food products still in production. This study evaluated the potential for translocation of Listeria monocytogenes from drains to food contact surfaces in the surrounding environment using Listeria innocua as a surrogate. A 7 × 7 × 8-foot polycarbonate flexi-glass chamber with a 10-inch-diameter drain mounted on an aluminum cabinet was used. Stainless steel coupons (6.4 × 1.9 × 0.1 cm, 12 per height) were hung at 1, 3, and 5 feet inside the chamber. Four treatment sets; non-inoculated, non-treated; non-inoculated, treated; inoculated, treated; inoculated non-treated; and two subtreatments of 8 h and 48 h were performed. For the inoculated sets, meat slurry (10 g of ground beef in 900 mL water) and a four-strain cocktail of Listeria innocua at 7 -8 log CFU/mL were used. For the treated sets, in addition, a commercial cleaner and sanitizer was applied. The drain was cleaned using a pressure hose (40 -50 psi) after 8 h and 48 h. Coupons were then removed and enriched in listeria enrichment broth to establish if any cell translocated from the drain onto the stainless steel coupons via aerosols generated during washing. Confirmation was done using VIP Listeria rapid test kits. Results indicated translocation at all three heights ranging from 2% -25%. Significantly higher translocation (p < 0.05) was found at 1 foot (up to 25%), followed by 3 feet (up to 11%) and 5 feet (up to 2.7%). This research indicated that translocation of Listeria spp. from drains to food contact surfaces does occur and increases with increased proximity to the drain.
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