Date of Graduation

5-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Food Science (PhD)

Degree Level

Graduate

Department

Food Science

Advisor/Mentor

Gibson, Kristen E.

Committee Member

Ricke, Steven C.

Second Committee Member

Lee, Jung A.

Third Committee Member

Marcy, John A.

Keywords

Food Microbiology; Food Safety; Food Science; Microbiology; Norovirus; Salmonella

Abstract

Detecting microorganisms on environmental surfaces via an environmental monitoring (EM) program is part of a preventive food safety culture. Environmental monitoring should 1) verify that food safety plans are reducing cross-contamination risk from surfaces to food, 2) pinpoint microbial niches, and 3) prevent the transmission of pathogens. Environmental monitoring programs utilize EM tools, such as sponges, to sample food contact and non-food contact surfaces. However, EM tool selection is determined by the individual food firm. This dissertation evaluated and characterized factors influencing EM program effectiveness in the food industry. Specifically, this dissertation focuses on the release of microorganisms from EM tools and the recovery of microorganisms from environmental surfaces. First, the release of microorganisms from EM tools was investigated. This study characterized polyurethane foam (PUF) and cellulose (CELL) EM tools for their ability to release foodborne pathogens (Listeria monocytogenes, Salmonella Typhimurium, Tulane virus [TV; human norovirus surrogate]) from their sponge matrices. This study aimed to 1) compare the ability of EM tools to release microorganisms, 2) characterize EM tool performance at decreasing inoculum concentrations, and 3) assess the impact of elution method during EM sample processing. Data indicated that EM tool type impacted microbial release (p=0.0001), whereas the PUF EM tool released microorganisms more readily than the CELL EM tool. Conversely, no significant differences were observed across inoculum levels or elution method (stomacher versus manual). Next, the influence of environmental factors on the recovery of microorganisms using the PUF EM tool was determined. The specific objective of this study was to determine if environmental conditions and surface composition impact the recovery of select microorganisms found in food processing environments. These data were compared across 1) microorganism type (L. monocytogenes, S. Typhimurium, TV), 2) surface type (polypropylene, stainless steel, neoprene), 3) environmental temperature and relative humidity (30°C/30%, 6°C/85%, 30°C/85%), and 4) exposure time (24 h or 72 h). Data indicate that microbial recovery from environmental surfaces significantly (p ≤ 0.05) varies by microorganism type, environmental conditions, and exposure time. However, overall, surface type did not significantly impact the recovery of microorganisms. Then, research focused on pathogen-food associated pairs and the impact of food residues on microbial recovery. Data generated from studies on L. monocytogenes and ready-to-eat food residues (lettuce rinsate, blended lettuce, whole milk, lowfat milk) suggest little variability in recovery amongst food residue types overall with greater differences apparent at the 24 h sampling period. Conversely, studies on S. Typhimurium and low water activity foods (all-purpose flour, whole milk dairy powder, infant formula) show significant differences in the mean log loss of S. Typhimurium (p < 0.05) between all food residue types at 1 h and 24 h sampling times. Moreover, significant differences were found within each food residue type over time. Overall, the findings within this dissertation provide insights on the factors that influence microbial release and recovery from EM tools utilized in the food industry. This information will assist the food industry in making informed decisions about EM programs and enhance EM protocols.

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