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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    UNDERSTANDING THE INTERACTIONS OF COLD ATMOSPHERIC PLASMA AND THE PLANT STRESS RESPONSE TO IMPROVE FRESH PRODUCE SAFETY
    (2023) Gilbert, Andrea Rochelle; Tikekar, Rohan V; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Cold atmospheric plasma (CAP) is a surface modification technology that produces oxidative species that inactivate microorganisms. This technology has been shown to be an effective sanitization technology for use on a variety of food products and leafy greens are a uniquely promising application. CAP products, such as reactive oxygen species (ROS), reactive nitrogen species (RNS), UV light, and ozone, are environmental stressors with antimicrobial effects that plants already encounter in their natural environment, and fresh produce will produce a stress response when treated by CAP and this stress response is not limited to directly treated tissue. The stress responses of baby spinach, red leaf lettuce, baby kale and live basil were evaluated post-CAP treatment. In all evaluated fresh produce CAP treatment resulted in a significant (p<0.05) increase in ROS. This increase in reactive oxygen species was not limited to the plant tissues directly treated by CAP. In live basil, ROS generation was detected on indirectly treated leaves sharing the same stem, and in spinach the increase in ROS levels continued for 12 hours post-treatment. To further understand how the elevated ROS levels affected plant tissues the flavonoid content was evaluated in baby spinach, red leaf lettuce and baby kale. Baby spinach CAP treatment resulted in a significant increase in flavonoids at 50w and 120w power level. Flavonoids in red leaf lettuce were only significantly affected in directly treated leaf tissue. In baby kale, CAP treatment significantly reduced flavonoid content in both direct and indirectly treated leaf tissue. To understand the differences between the two leafy greens species and the effect of ozone and UVB treatment, two products treated with CAP, were also evaluated on baby spinach and baby kale. The two non-CAP treatments resulted in the opposite effects in baby spinach and baby kale, and an examination into the response of the stress hormones salicylic acid and jasmonic acid was inconclusive. The novel interactions of this sanitization treatment with the plant stress response may provide useful opportunities to improve both the food safety and nutritional quality of fresh produce. In addition to the research project, I composed a needs assessment survey instrument to evaluate food safety compliance among small and very small food processors in the northeastern United States in cooperation with the Northeast Center for the Advancement of Food Safety. The survey instrument was sent to food safety professionals and regulators in the region. Results of the survey revealed that the food safety concepts that processors struggled to learn were often those cited by regulators during inspections. 
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    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.