Predicting initial transformation products of food-based bio-polymers and -molecules during food disinfection

Starting in the early 1900s, chlorinating potable water supplies dramatically reduced the incidence of waterborne diseases. However, in the 1970s, analytical chemists discov-ered trihalomethanes (THMs) as byproducts of chlorination reactions with natural organic matter (NOM) in drinking water. Although greater than 600 disinfection byproducts (DBPs) have since been characterized in drinking water, regulations continue to focus on THMS and haloacetic acids (HAAs). With recent toxicological studies demonstrating that other DBPs have orders of magnitude higher toxic potencies than THMs and HAAs, cur-rent research has shifted to focus on characterizing newer classes of DBPs that could con-tribute to toxicity. However, these investigations remain arduous due to the difficulty in characterizing DBP precursors found in NOM. Nonetheless, research using amino acids and other model precursors demonstrates that yields of THMs and HAAs are < 1% due to the difficulty of breaking carbon-carbon bonds to liberate these 1-2 carbon byproducts from larger precursor structures. Identifying the higher-yield initial products of chlorine addition to components of NOM has been difficult because the structures of these NOM compo-nents are unclear. With regards to food, pathogenic outbreaks are still prevalent. It is estimated that foodborne pathogen outbreaks now exceed those in drinking water. Free chlorine is the most widely used food disinfectant. Although chlorine exposures required for food wash-ing in packaging facilities have not yet been codified, chlorine doses (50-200 mg/L as Cl2) and precursor concentrations (solid food) are much higher than encountered in drinking water. Although research on the formation of DBPs in chemically disinfected foods has been published, these studies tend to focus on the same low-yield DBPs (e.g., THMs) that are the focus of drinking water research. They are unlikely to represent an exposure con-cern in food because they tend to partition to the washwater rather than the food. In con-trast, the structures of the biomolecular precursors in food (e.g., the amino acids constitut-ing protein and the fatty acids constituting lipids) are well-characterized. Instead, I argue that the initial products of chlorine addition to amino acids and fatty acids will be of greater importance for consumer exposure since they will form at high yield and remain bound in food matrices. This dissertation introduces (chapter 2) the reader to: the necessity of food disinfec-tion, food processing, mechanisms of disinfection by chlorine and ozone, and the study of food disinfection byproducts as the backdrop for understanding the subsequent chapters. Following this introduction, the dissertation uses the formation of chlorotyrosines from protein-bound tyrosines in produce as a model for the initial chlorine addition products to proteins within produce and demonstrates their importance as toxicity drivers relative to the 1-2 carbon DBPs of current research interest (chapter 3). Finally, this work (chapter 4) shows the formation of fatty acid chlorohydrins from lipid-bound fatty acids as a model for the initial chlorine addition products to lipids inside chlorine-treated produce. Overall, this dissertation shows the complexity of food disinfection byproduct research, and the need for further investigation of these contaminants as potentially dominant components of the over-all toxic exposures

Advisor: Mitch William A. 
Criddle Craig
Luthy Richard G.
Tarpeh William