Author ORCID Identifier:

https://orcid.org/0009-0002-3113-0003

Date of Graduation

8-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Food Science (PhD)

Degree Level

Graduate

Department

Food Science

Advisor/Mentor

Acuff, Jennifer

Committee Member

Gibson, Kristen

Second Committee Member

Adams, Rich

Third Committee Member

Kwon, YoungMin

Keywords

Cleaning; Dry Environment; Food safety; Low moisture food; Sanitation; Stainless steel surface

Abstract

Low-moisture food (LMF) processing environments pose a persistent food safety risk due to Salmonella survival and harborage on surfaces. This work investigates persistent bacterial populations (PBPs) in LMF production environments, focusing on identifying a suitable surrogate and evaluating sanitation strategies. Three potential surrogates, Escherichia coli MP 26, Enterococcus faecium, and Pediococcus acidilactici, were compared to Salmonella PBPs formed in nonfat dry milk (NFDM) on stainless steel coupons stored at 25°C under 30% or 70% relative humidity (RH) using two different inoculation methods. E. faecium showed survival patterns most similar to Salmonella, with no significant differences in log reductions (p > 0.05), while the others were significantly more sensitive to the desiccation (p < 0.05). Additionally, impacts of the same environmental factors on cross-contamination potential were evaluated for high (7–8 log CFU) or low (3–4 log CFU) Salmonella Tennessee inocula in a PBP on stainless steel. After storage, coupons were vortexed with 10 g of non-inoculated NFDM. The highest transfer (5.3 log CFU/g) occurred with the slurry method at 30% RH after 7 days in the high-inoculum group, while transfer of 3.5 log CFU/g was observed in the low-inoculum group. Transfer was significantly affected by RH, inoculum level, and inoculation method (p < 0.05). Finally, sanitation efficacy was assessed using dry (i.e., manual scraping to remove visible debris without water) and wet cleaning (application of sanitizer followed by manual scraping) followed by quaternary ammonium compound (QAC), isopropyl alcohol (IPA), or thermal treatment. IPA alone reduced Salmonella by 0.2 log CFU/cm² in a powdered peanut butter (PB) matrix; this increased to 3.0-log and 4.8-log reductions with dry or wet cleaning, respectively (p < 0.05). Thermal treatment (135°C, 30 min) achieved up to 8-log CFU/cm² reduction when preceded by dry cleaning (scraping). QAC showed lower efficacy than other treatments. Matrix composition strongly influenced outcomes, with PB offering the most protection against sanitizing treatments. E. faecium broadly mirrored Salmonella trends but was often more sensitive to certain treatments, making it a practical but occasionally non-conservative surrogate.

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