Food Science and Technology Department


First Advisor

Byron D. Chaves

Date of this Version





A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Food Science & Technology, Under the Supervision of Professor Byron D. Chaves. Lincoln, Nebraska: July 2021

Copyright © 2021 Cyril Nsom Ayuk Etaka


Small and very small food facilities in the ready-to-eat food industry face difficulties complying with the Food Safety Modernization Act-Preventive Controls for Human Food rule (FSMA-PCHF). This regulation highlights the need for sanitation to control environmental pathogens like Listeria monocytogenes. The main goal of this project was to investigate the prevalence and control of Listeria monocytogenes in food facilities. This study provides technical assistance to facilities to comply with the PCHF rule and addresses sanitation alternatives for food contact surfaces like aqueous ozone.

First, the prevalence of Listeria spp and L. monocytogenes in small and very small food manufacturing facilities in Nebraska was determined. In this study, environmental samples were collected from three participating facilities. Overall, Listeria spp were detected in 14 of 266 (5.3%) samples with sites like floors and drains having the highest prevalence. No significant difference in prevalence across all three facilities was observed. Listeria monocytogenes was not detected in any of the facilities. This study highlights the importance of management and sanitation of non-food-contact surfaces like drains and floors. Our data was provided to participating facilities to assist in starting their environmental monitoring program and overall, contributing to their compliance with the PCHF rule.

Next, we determined the efficacy of ozonated water for the decontamination of Listeria on food contact surfaces. For this study, stainless steel and polypropylene coupons constructed to 10 x 10 cm were conditioned with organic matter made from uncured deli turkey breast and inoculated with Listeria monocytogenes. Other experiments were performed with Listeria innocua separately. Clean coupons were also included for experiments with L. innocua. Inoculated surfaces were exposed to 10 ppm of ozonated water for 15, 30, and 45 seconds. Tap water was included as a treatment. There were no significant differences in reductions attributed to ozonated water compared to tap water washing. However, reductions of L. innocua on soiled stainless steel were significantly higher than on clean surfaces(P = 0.01). Similarly, L. innocua reductions were numerally higher on soiled polypropylene though not significantly different from clean coupons. Spraying applications may have influenced bacterial reduction from surfaces by dislodging rather than actual inactivation. In addition, the soil system with deli turkey may have not provided sufficient soil (grease) to reduce the efficacy of ozonated water resulting in similar reductions on both soiled and clean surfaces. Overall, data suggest that cleaning may be effective at reducing transiently attached Listeria from FCS.

Advisor: Byron D. Chaves