Food Science and Technology Department


First Advisor

Andréia Bianchini-Huebner

Second Advisor

Jayne Stratton

Date of this Version

Fall 12-4-2020


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 and Technology, Under the Supervision of Professor Andréia Bianchini-Huebner. Lincoln, Nebraska: December, 2020

Copyright © 2020 Karen Andrea Nieto Flores


Listeria monocytogenes can survive and grow under wet environmental conditions encountered in dairy facilities. Pasteurization of milk kills L. monocytogenes; however, recent listeriosis outbreaks have linked post-pasteurization contamination from the food environment to the final product. One of the sources of microbial contamination may include employees and their personal protective equipment (PPE), which often become in contact with equipment and food contact surfaces. To understand this issue, this study evaluates Listeria innocua, as a surrogate for Listeria monocytogenes, transfer from PPE to food products and surfaces encountered in dairy plants. Gloves, aprons, and boots were inoculated with L. innocua using Phosphate Buffer Saline (PBS) and skim milk as bacterial carriers. Overall, PPE contaminated in the presence of skim milk led to higher bacterial transfer to the surfaces under evaluation, than those inoculated using PBS. With PBS, consecutive touches led, for some PPE/surface combinations, to a decline in transfer; however, with skim milk no decline in transfer was observed. This study also evaluated the effectiveness of chlorine, quaternary ammonia, and peroxyacetic acid (PAA) in reducing L. innocua contamination from PPE. When sanitizers were used by themselves, the most effective was PAA. For all sanitizers tested, effectiveness was greatly reduced in the presence of organic matter. Therefore cleaning regimes that included cleaning and scrubbing steps, followed by the use of a sanitizer, were evaluated. With the proposed cleaning regime more than 3-log reductions were achieved in the different types of PPE even when organic matter (skim milk inoculum) was present.

Advisor: Andréia Bianchini