UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item The Development of a Qualitative Risk Assessment and Targeted Storage Decline Kinetics Data as Critical Components for Developing a Full Quantitative Risk Assessment of Salmonella Contamination in Milk Chocolate(2019) Oni, Ruth Adeola; Buchanan, Robert L; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Salmonella enterica infections and outbreaks have been associated with chocolate consumption over the last four decades. The source of contamination for these occasional salmonellosis outbreaks are often unidentified, and typically the level of contamination is only a few salmonellae per serving. The main goals of this dissertation were to collate relevant scientific information regarding microbial safety of milk chocolate, conduct a qualitative assessment of risk factors for Salmonella contamination encountered during the complex processes of cocoa bean cultivation and the subsequent process of milk chocolate manufacturing, and to generate targeted data and survival models for kinetics of Salmonella stored in milk chocolate crumb; all components critical to the development of a stochastic quantitative microbial risk assessment. The farm-to-packaging qualitative assessment provided categorizations of risk for relevant activities and ingredients, identified critical data gaps and “risk spots” and culminated in an Excel-based risk rating tool used to illustrate the usability of the qualitative assessment. Results indicate an overall low residual risk of Salmonella contamination of a packaged milk chocolate product for a base model, provided dictates of process control measures are rigorously adhered to, and the risk rating tool enables the assessment of what-if scenarios for deviations from optimal practices. One of the data gaps identified in the qualitative risk assessment led to investigation into the use of milk chocolate crumb, an intermediate product during milk chocolate processing, and its potential association with Salmonella risk. Evaluation of the survival kinetics of S. enterica in milk crumb showed a significant (p<0.05) dependence of survival on storage temperature, strain and crumb type. Due to the manner in which crumb is generally utilized during milk chocolate processing, findings from this study are the first to link the use of crumb and Salmonella risk, and presents promising opportunities for risk reduction which can be explored through further research into optimization of crumb storage parameters. This study serves as a valuable resource to food safety stakeholders in the chocolate industry as it builds the foundation and provides much-needed data for a quantitative microbial risk assessment model that can be used to optimize food safety control programs.Item The Role of Organic Matrices (dried turkey manure) in the Contamination and Survival of Salmonella spp. on Baby Spinach Leaves(2012) Oni, Ruth Adeola; Buchanan, Robert L; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microbiological safety of fresh produce has attracted attention due to constant produce outbreaks. Manure contaminated with enteric pathogens has been identified as a major pre-harvest contamination source. This study investigated the survival of Salmonella in dust particles generated from dehydrated turkey manure, and how this could serve as an airborne contamination of leafy greens. Laboratory trials of the UV resistance of Salmonella in manure dust were also conducted to assess its protective effect; along with greenhouse studies to determine the survival of Salmonella in manure dust on spinach leaves. Results indicate survival times were inversely related to moisture content and particle size of manure dust. The presence of manure particles substantially enhanced the pathogen's survival under UV and reduced its inactivation on spinach leaves. This study presents data that could be used to assess the potential role of aerosolized manure as a pre-harvest risk factor for contamination of leafy greens.