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 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.Item Photoirradiated Caffeic Acid as an Antimicrobial Treatment for Fresh Produce(2017) Gilbert, Andrea Rochelle; Tikekar, Rohan V; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The antimicrobial efficacy of 400 nm photoirradiated caffeic acid (CA, 5 mM) was evaluated against Escherichia coli O157:H7 and Listeria innocua. A stronger antimicrobial effect was observed on E. coli than on L. innocua where the combined treatment resulted in 4 and 1 log CFU/mL reductions, respectively. The treatment’s effects on metabolism (resazurin assay), uptake of CA (fluorescence technique) and membrane damage (prodpidium iodide assay) were studied in both species. CA uptake increased in both species, but membrane damage was only observed in E. coli. The treatment had minimal impact on metabolic activity in both species. The treatment applied to the surface of spinach leaves was found to be effective against E. coli. A combined treatment of 400 nm light and plant extracts known to contain CA was also evaluated for antimicrobial activity against E. coli and found to be effective. The novel treatment proposed in this study has the potential to improve the microbial food safety of fresh produce.