Date of Graduation

5-2012

Document Type

Thesis

Degree Name

Master of Science in Food Science (MS)

Degree Level

Graduate

Department

Food Science

Advisor

Philip G. Crandall

Committee Member

Steven C. Ricke

Second Committee Member

Navam S. Hettiarachchy

Third Committee Member

Jean-François Meullenet

Keywords

Biological sciences; Disinfection; Food safety; Listeria monocytogenes; Microbial contamination; Moist heat; Viable-but-non-culturable state

Abstract

The overall objectives of this study were to: evaluate the efficacy of different cleaning cloth types and cloth-disinfectant combinations in reducing food contact surface contamination to acceptable levels; determine the optimum moist heat and moist heat + sanitizer treatments that can significantly reduce the number of Listeria strains on deli slicer components; and investigate if the moist heat treatment used in this study induced the viable-but-non-culturable (VBNC) state in Listeria cells. The efficacy of wiping cloths was measured using ATP-bioluminescence and total plate count methods using four different wiping cloths and silver dihydrogen citrate sanitizer on food contact surfaces. The lethality study of moist heat and silver dihydrogen citrate disinfectant against Listeria strains was done using deli slicer components and the viable-but-non-culturable state of Listeria strains subjected to sub-lethal moist heat and silver dihydrogen citrate disinfectant stresses was measured using BacLight bacterial viability test kit. In the first study we demonstrated that the cleaning effects of wiping cloths on food contact surfaces can be enhanced when used with the SDC sanitizer and stated that the ATP-B measurements can be used for real-time hygiene monitoring in the public sector with inclusion of microbial contamination testing (total plate count) for more reliable measure of cleanliness. In the moist heat lethality study, the internal moist heat only treatment and both the internal and external moist heat + disinfectant treatments yielded non-detectable levels of Listeria strains on stainless steel and cast aluminum coupons. Moist heat only and moist heat + disinfectant treatments at 150 °F (66°C) and at least 20% relative humidity (RH) for 5 h was adequate to attain non-detectable levels of a Listeria strains cocktail on both stainless steel and cast aluminum deli meat slicer components. The BacLight bacterial viability test demonstrated that the moist heat treatment applied in this study was effective in inactivating Listeria strains. However, the absence of growth on nutrient agar plates and detection of live cells by the viability test demonstrated that the sub-lethal temperature used in this study could induce the VBNC state in Listeria strains.

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