Nutrition & Food Science

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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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    EVALUATION OF THE COPPER HOMEOSTASIS AND SILVER RESISTANCE ISLAND AND ITS ROLE IN PERSISTENCE OF SALMONELLA ENTERICA
    (2023) Haendiges, Julie; Tikekar, Rohan; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Salmonella enterica is one of the leading bacterial cause of foodborne illness in the UnitedStates. Although there are many serovars, only a small subset causes human illness. Since Salmonella is ubiquitous in the environment, the Food and Drug Administration has established regulations for food processors to ensure that the products are free of contamination. Low-moisture foods are commonly ready-to-eat, and due to the low water activity do not promote growth of bacteria. However, Salmonella has been shown to persist in these foods. There havebeen two outbreaks and multiple recalls in the United States due to contaminated pistachios. Based on a retrospective study, results show that there is evidence of a contamination in the growing orchard and a significant number of Salmonella isolates from the environments contain the Copper Homeostasis and Silver Resistance Island (CHASRI) cassette. This raises several questions: what is the prevalence of CHASRI among different Salmonella isolates from food and environmental sources? Does presence of CHASRI enable Salmonella to survive better against copper stress? And whether presence of CHASRI provide cross-protection against other stresses such as desiccation and thermal treatment? This dissertation attempts to answer those questions. The prevalence of the CHASRI in Salmonella was determined by the use of publicly availablewhole genome sequencing data. The CHASRI was found in 61 different serovars and types of sources. The presence of the CHASRI in isolates from low-moisture foods that have caused previous outbreaks (peanut butter, nuts, spices) was interesting to note, and leads to future studies on correlations between this island and virulence. Based on results of phylogenetic analysis of CHASRI sequences from closed genomes, we determined there were four types of CHASRI found in Salmonella. Traditionally, the Salmonella Genomic Island-4 (SGI-4) is found but in addition the CHASRI can incorporate by itself, within a variant of SGI-4, or via a rare plasmid. Interestingly, the sequence of the CHASRI from SGI-4 and the variant SGI-4 were highly different. The high SNP differences in sequence along with the difference in the arsenic operon led to the conclusion that these variants arose independently. A Salmonella Senftenberg strain (CFSAN047523), isolated from pistachios, was used to createthree knockouts (∆cus, ∆pco, and ∆CHASRI). Previous studies have looked at the minimum inhibitory concentration (MIC) of strains with and without the CHASRI but have omitted the minimum bactericidal concentration (MBC). In this study, we used the knockouts to test for both MIC and MBC. While the MIC was similar for the strains, the MBC was greater in the wild type and partial CHASRI knockouts. Growth and inactivation kinetics were measured in different concentrations of copper sulfate. At higher levels of copper sulfate, the presence of the CHASRI made cells more resilient to inactivation by copper sulfate. Evidence shows that the stress response in Salmonella has the ability to crosstalk and provideprotection against multiple stresses. To investigate this phenomenon further, our isolates were tested against a multitude of stresses to evaluate for cross-protection that may be due to theCHASRI. Cells undergoing copper stress were better equipped to survive lethal copper concentrations and desiccation if the CHASRI was present. The presence of Salmonella in final pistachio products that have been fully processed identifies that some adaptation and stress response is occurring in the processing facility. Inoculated pistachios with the wild type and ∆CHASRI strain were thermally processed to test for survivors. This study showed that the presence of the CHASRI gave the isolate an advantage to survive thermal processing after desiccation. Overall, this study presents the prevalence of the CHASRI in Salmonella enterica as well as theimportant role it plays in copper tolerance. The evidence of cross-protection and tolerance to copper leads to future research regarding gene expression and virulence assessment.
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    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.
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    The Antimicrobial Effect of Benzoic Acid or Propyl Paraben Treatment combined with UV-A Light on Escherichia Coli O157:H7
    (2017) Ding, Qiao; Tikekar, Rohan V; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The antimicrobial effect of the combined UV-A light and benzoic acid (BA) or propyl paraben (PP) treatment was evaluated using Escherichia Coli O157:H7. Factors affecting the efficacy of antimicrobial treatments were examined through various microbial and biochemical approaches. A combined 15 mM BA and UV-A treatment exhibited more than 5 log (CFU/mL) reduction in antimicrobial activity via production of reactive oxygen species (ROS), membrane damage and decreasing intracellular pH. Similarly, the combined 3 mM PP and UV-A treatment also caused more than 5 log reduction contributed by membrane damage. UV-A and BA treatment was also found to be effective in a scaled-up, continuous system, while a combined UV-A and PP was able to significantly reduce the likelihood of cross-contamination in simulated fresh produce washing study. The findings from this study have revealed the potential for the combined treatments that help to improve the safety and quality of fresh produce.
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    Portable Hyperspectral Imaging Device for Surface Sanitation Verification in the Produce Industry
    (2011) Wiederoder, Michael; Lo, Y. Martin; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Produce processors must clean and sanitize surfaces before production to reduce the risk of foodborne illness. Current surface hygiene verification methods require direct surface sub-sampling at selected locations and a wait time. To augment these methods, a portable hyperspectral imaging device was developed to find potential contaminants in real-time and increase sub-sampling effectiveness. Analysis of hyperspectral fluorescence images showed that fresh-cut produce processing exudates in the regions of 460-540 and 670-680 nm are detectable from background materials, while select cleaning agents are not. The portable single operator imaging system includes a charge coupled device (CCD) camera, tunable optical filter, laptop, light emitting diodes (LED's) for fluorescence excitation, and a touchscreen display. Within a commercial plant, fluorescence imaging identified produce processing residuals following routine cleaning procedures that were not readily visible to the naked eye. These tests demonstrate the system's potential to enhance post-cleaning inspection, and helped improve routine cleaning procedures.
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    Assessment of Foodborne Pathogen Survival During Production and Pre-harvest Application of Compost and Compost Tea
    (2009) Ingram, David Thomas; Joseph, Sam W; Meng, Jianghong; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The use of compost in crop production systems as a soil amendment is recognized by both conventional and organic plant production practitioners as a means to increase yields and reduce the incidence of foliar diseases. Compost tea (CT), an aqueous extract of the biological components of compost, is also recognized as a means to broadcast the phytopathogen-reducing components of compost directly to the surfaces of plants where many foliar diseases become established. CT has been shown to control the proliferation of a variety of foliar diseases in many turf, crop and horticulture production systems when applied directly to the foliar surfaces of plants. This dissertation research was designed to address several pre-harvest food safety issues concerning compost and compost teas. Three objectives were pursued to establish whether the use of compost and compost teas as pre-harvest practices may introduce foodborne pathogens into the food supply and, therefore, contribute to the incidence of foodborne illness. The first objective involved a microbiological survey of commercially available compost in the U.S. to determine the prevalence of fecal coliforms, Escherichia coli, Salmonella and enterococci that might be reaching consumers through contaminated fruit and vegetables. The second objective was to investigate the ability of these foodborne pathogens to propagate during the production of CT. The third objective involved a field study examining the potential of CT to disseminate E. coli into organic and conventional strawberry production systems. The effects of CT on the fruit yield, phytopathogen suppression, as well as the potential for foodborne pathogen survival on the fruit surfaces were examined. This project provided important information and recommendations for the safe production and pre-harvest application of compost and compost teas. It was contended that, with proper attention to the manufacture and storage of compost and with simple modification of current trends in CT production systems, the current threshold of pre-harvest introduction of foodborne pathogens could be significantly reduced.
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    Biofilm formation by Escherichia coli O157:H7
    (2007-12-14) Silagyi, Karen Suzanne; Lo, Y. Martin; Kim, Shin-Hee; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Escherichia coli O157:H7 from cattle was evaluated for its ability to produce biofilm on food contact surfaces and quorum sensing signals in various raw meat, raw poultry, and produce broths. Generally, the strain was able to attach and form the most biofilm on stainless steel. Transfer of cells attached to stainless steel was observed onto various raw meat, raw poultry, ready-to-eat deli meats, and produce products as high as 104 CFU/cm2. E. coli O157:H7 isolated from 14 animal, food, and human sources were characterized on antimicrobial susceptibility, ability to form biofilm, and production of curli fimbriae and cellulose. Strains isolated from cattle, retail chicken, and retail beef were able to form strong biofilms in addition to curli and cellulose production. Additionally, E. coli O157:H7 from retail chicken showed considerable antimicrobial resistance. This study suggests E. coli O157:H7 biofilms pose significant risk to continuous contamination of a variety of food products.