Date of Award
Doctor of Philosophy
Food Science and Human Nutrition
Byron F. Brehm-Stecher
Infectious diseases caused by established foodborne pathogens, multidrug-resistant bacteria and opportunistic fungal pathogens pose serious threats to both public health and the economy. The aim of this work was to provide new approaches based on natural or value-added agricultural materials to address these important threats. Chapter 1 of this thesis provides a general introduction and description of how the work is organized. Chapter 2 reviews the literature related to our topics of research and Chapter 8 provides general conclusions. The remaining chapters report on the various projects that were conducted on the topics of natural and value-added approaches for pathogen control. Specifically, the cationic vegetable oil-based polyurethane dispersions and coatings described in Chapters 3, 4 and 5 of this work displayed promising antimicrobial properties against multiple human pathogens of both clinical and foodborne concern. The antimicrobial properties of these coatings were determined using a variety of cultural and instrumental approaches. Cultural methods included disk diffusion tests, time course plating and broth microdilution assay using a Bioscreen C Microbiological Reader. Instrumental approaches included flow cytometry for determination of cell membrane permeability, fluorescence and light microscopies for determining changes in cell and colony morphology and spectrophotometry for measuring the release of intracellular compounds. The use of multiple antimicrobial testing strategies allowed us to more fully characterize the cellular effects of polymer treatment and to gain clearer insight into polymer mode(s) of action (MOA). An understanding of MOA may help identify potential benefits and limitations of the practical use of these polymers in medical or food-related environments.
Over the last three decades, Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes have emerged as the three most prevalent bacterial pathogens causing outbreaks in fruits and vegetables. Natural antimicrobial systems capable of inactivating these pathogens could provide attractive clean-label solutions for enhancing produce safety. In Chapters 6 and 7, antimicrobial hurdle systems comprised of GRAS natural antimicrobials having complementary or interactive modes of action were developed and examined. Systems containing Grape Seed Extract, long-chain sodium polyphosphate (polyP) and various organic acids were found to be effective against E. coli O157:H7 and S. Typhimurium in both broth culture and in lettuce extract, a simulant for the plant-based organic materials expected in produce processing waters and which may challenge the efficacy of applied antimicrobials. Data gathered using various methods demonstrated that use of polyP resulted in enhancement of GSE against L. innocua or L. monocytogenes. Lastly, pronounced differences in the antimicrobial efficacy of two commercial GSE’s were observed, suggesting that intrinsic biological or preparative variations resulting in different levels of antimicrobially-active polyphenolic components might be important for practical use of this ingredient. A greater understanding of the biochemical basis of these variations, coupled with quality control and standardization is needed before GSE can be widely adopted by the fresh produce industry.
Together, the studies presented in this thesis provide natural and value-added approaches for pathogen control that may be useful in both medical and food production applications.
Zhang, Zongyu, "Natural and value-added approaches for pathogen control" (2015). Graduate Theses and Dissertations. 14726.