Effects of Inoculation Level, Material Hydration, and Stainless Steel Surface Roughness on the Transfer of Listeria monocytogenes from Inoculated Bologna to Stainless Steel and High-Density Polyethylene

• Published in: Journal of food protection Vol. 70; no. 6; pp. 1423 - 1428
• Main Authors: Rodriguez, A, Autio, W.R, McLandsborough, L.A
• Format: Journal Article
• Language: English
• Published: Des Moines, IA International Association of Milk, Food and Environmental Sanitarians 01.06.2007
• Subjects: Bacterial Adhesion - physiology; bacterial contamination; Biological and medical sciences; bologna; Colony Count, Microbial; Consumer Product Safety; Equipment Contamination; food contact surfaces; Food Contamination - analysis; Food Contamination - prevention & control; Food industries; Food Microbiology; food pathogens; food processing equipment; food processing plants; Food-Processing Industry - methods; Food-Processing Industry - standards; Fundamental and applied biological sciences. Psychology; Humans; inoculum density; Listeria; Listeria monocytogenes; Listeria monocytogenes - growth & development; Listeria monocytogenes - physiology; Meat and meat product industries; meat processing; Meat Products - microbiology; Polyethylene; Pressure; Stainless Steel; surface roughness; Time Factors; Water - metabolism; water activity; water content; Italy, Bologna; Polyethylene; Sausage; Hydration; Materials; Roughness; Meat product; Pork product; Listeria monocytogenes; Density; Surface; Inoculation; Stainless steel; Transfer; Bacteria
• ISSN: 0362-028X; 1944-9097
• DOI: 10.4315/0362-028X-70.6.1423

The influence of inoculation level, material hydration, and stainless steel surface roughness on the transfer of Listeria monocytogenes from inoculated bologna to processing surfaces (stainless steel and polyethylene) was assessed. Slices of bologna (14 g) were inoculated with Listeria at different levels, from 10(5) to 10(9) CFU/cm2. Transfer experiments were done at a constant contact time (30 s) and pressure (45 kPa) with a universal testing machine. After transfer, cells that had been transferred to sterile stainless steel and polyethylene were removed and counted, and the efficiency of transfer (EOT) was calculated. As the inoculation level increased from 10(5) to 10(9) CFU/cm2, the absolute level of transfer increased in a similar fashion. By calculating EOTs, the data were normalized, and the initial inoculation level had no effect on the transfer (P > 0.05). The influence of hydration level on stainless steel, high-density polyethylene, and material type was investigated, and the EOTs ranged from 0.1 to 1 under all the conditions tested. Our results show that transfers to wetted processing surfaces (mean EOT = 0.43) were no different from dried processing surfaces (mean EOT = 0.35) (P > 0.05). Material type was shown to be a significant factor, with greater numbers of Listeria transferring from bologna to stainless steel (mean EOT = 0.49) than from bologna to polyethylene (mean EOT = 0.28) (P < 0.01). Stainless steel with three different surface roughness (Ra) values of <0.8 micrometer (target Ra = 0.25, 0.50, and 0.75 micrometer) and two different finishes (mechanically polished versus mechanically polished and further electropolished) was used to evaluate its effect on the transfer. The surface roughness and finish on the stainless steel did not have any effect on the transfer of Listeria (P > 0.05). Our results showed that when evaluating the transfer of Listeria, the use of EOTs rather than the absolute transfer values is essential to allow comparisons of transfer conditions or comparisons between research groups.