The study investigated the degree of cross-contamination between deli foods and slicers by Listeria monocytogenes, Salmonella, and E.coli O157:H7 and their inactivation by levulinic acid (LA) plus sodium dodecyl sulfate (SDS).
Results revealed that cross-contamination is possible between deli foods and slicers and LA-based sanitizer applied as foam can remove microbial contamination on the slicers.
The antimicrobial efficacy of the LA + SDS sanitizers applied as a liquid or as foam at three concentrations was determined for decontamination of the pathogens on the slicers at 21 °C.
Concentrations were 0.5% LA + 0.05% SDS, 1% LA + 0.1% SDS, and 2% LA + 0.5% SDS.
After 10 slices, the pathogens from slicer blades were significantly less than the recovery from some other contact locations.
When the slicer blades were contaminated with L. monocytogenes, S. Typhimurium, or E. coli O157:H7 at ca. 8.5 log CFU/blade, the slicing operation contaminated up to 61 consecutive slices.
Treating slicer blades with a liquid solution of 2% levulinic acid plus 0.5% SDS killed all three of the pathogens by 6-8 log CFU/blade within 1 minute.
Foam solutions, applied at equivalent or lower concentrations of levulinic acid plus SDS, reduced the three pathogens at all of the contact times evaluated.
The researchers said application of sanitizers as a foam may be more practical to reduce the risk of cross contamination as they could penetrate hidden areas.
The three pathogens had the ability to survive on dried surfaces of the slicers for at least six days, they added.
Outbreaks of L. monocytogenes, Salmonella and E. coli O157:H7 have been associated with deli food products, and cross-contamination during slicing has been suspected as the mode of transmission.
Quaternary ammonium-based sanitizers are commonly used by the industry to sanitize slicers, said the study.
The three slicers were new and used for the first time. Before and after each use, slicers were cleaned with detergent, rinsed with sterile distilled water, and treated with 70% ethanol.
Deli Swiss cheese, roasted black forest ham, and roast beef were surface-inoculated with L. monocytogenes, S. Typhimurium, and E. coli O157:H7 mixtures.
Swabbing locations included the meat grip, carriage tray, gauge plate, slicer blade and blade cover.
The three pathogens were transferred at a rate of 1-4 log CFU/10 cm2 from the surface of contaminated deli foods to slicer surfaces, with no significant difference among the mean or total transfer rates.
L. monocytogenes and E. coli O157:H7 recovered from the blades were significantly less than the cell numbers from the meat grips and carriage trays, whereas the least cell numbers of S. Typhimurium were recovered from the blade among the five contact locations.
The enrichment broths for L. monocytogenes, S. Typhimurium, and E. coli O157:H7 were Fraser broth, Selenite broth, and TSB plus nalidixic acid (50μg/ml).
Source: Food Microbiology, Volume 38, April 2014, Pages 263–269
Online ahead of print, DOI: 10.1016/j.fm.2013.10.004
“Transfer of foodborne pathogens during mechanical slicing and their inactivation by levulinic acid-based sanitizer on slicers”
Authors: Dong Chen, Tong Zhao, Michael P. Doyle