Masters Theses

Orcid ID

Date of Award


Degree Type


Degree Name

Master of Science


Food Science and Technology

Major Professor

Faith J. Critzer

Committee Members

Curtis R. Luckett, Mark T. Morgan, Annette L. Wszelaki


As a result of previous outbreaks associated with packinghouse contamination and in conjunction with new regulatory requirements, environmental monitoring targeting Listeria monocytogenes has been recommended for packinghouses. However, there is an overall lack of knowledge regarding problem areas in the packinghouse. Absence of sufficient environmental monitoring programs have left growers and packinghouse operators ill-equipped to effectively monitor for Listeria species, a common indicator group for L. monocytogenes. A better understanding of Listeria spp. in the packing environment is required, in addition to an easily implemented method for conducting site-specific risk analysis to effectively target and eliminate foodborne pathogens during packing and between harvesting seasons. Three tomato packinghouses were sampled for presence of Gram-positive bacteria and Listeria spp. on zone 1 contact surfaces during the 2017 harvesting season. A designated surface area of 100 cm2 [square centimeters] was sampled and stored in Dey Engley neutralizing buffer. Gram-positive bacteria were spiral-plated on Modified Oxford Medium (MOX) and incubated for 48 h [hours] at 35 °C [degrees Celsius]. A 1-ml [milliliter] sample was also enriched and streaked on MOX for basic detection of Listeria spp. Presumptive positive samples were confirmed with PCR. Additionally, common food-grade materials used in packinghouse environments were also collected and evaluated to describe differences in attributes between materials that could affect microbial harborage or sanitation effectiveness. Materials were assigned numerical ratings for each value that were combined with microbial data to issue a resistance to clean score, which described cleanability of that material. While evidence of microbial harborage was not observed throughout sampling, several niche points were established as areas for potential attachment of Listeria spp. after sanitation. Additionally, a methodology was developed for growers and packinghouse operators to utilize to evaluate their equipment for areas that may be of greater risk to the integrity of their food safety system. This methodology can be implemented to enable the development of a more targeted approach to eliminating Listeria spp. in the packinghouse.

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