Nutrition & Food Science Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2798
Browse
14 results
Search Results
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 CHARACTERIZATION, DISTRIBUTION, AND EVOLUTIONARY ACQUISITION OF ANTIMICROBIAL RESISTANCE ELEMENTS AMONG DIVERSE SALMONELLA SUBSPECIES(2017) Kroft, Brenda; Meng, Jianghong; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Insights into the evolution of antimicrobial resistance can be gleaned by examination of historical strains of Salmonella collected from a variety of locations, time periods, and sources. Here, the Salmonella Reference Collections were utilized to gain evidence into the distribution, prevalence, and reticulate nature of antimicrobial resistance from strains that represent the collective genetic diversity of Salmonella. Of the 141 strains examined, 25.5% were fully or intermediately resistant to one or more agents. Resistance to the older antimicrobials sulfisoxazole and streptomycin were more common than resistance to newer antimicrobials, with 15.6% and 14.2% of strains resistant, respectively. No strains presented with resistance to newer drugs--ciprofloxacin, cefoxitin, and ceftiofur specifically. Of particular importance was the identification of a correlation between strains isolated from food animal sources and the presence of resistance to streptomycin and kanamycin, as food animals have been implicated in the transfer of resistance elements through the food chain. Increased incidences of resistance were identified in serotypes Saintpaul, Heidelberg, and Typhimurium. Integrons, a major contributor to the horizontal transfer of resistance genes, were identified in 9.93% of strains and the most commonly harbored gene was aadA1, conferring resistance to streptomycin. Identification of exogenous genes responsible for the observed phenotypes revealed that 73.1% of resistant phenotypes could be accounted for by the presence of such an element. Analysis of horizontal gene transfer among the regulatory mar, ram and sox operon regions, which have been implicated in the development of multi-drug resistance via increased cellular efflux, revealed that recombination helped to maintain a handful of presumably beneficial alleles across subspecies I S. enterica. Diversification was particularly limited in the sox operon and in the global regulatory genes, as opposed to local regulators. Such lack of diversity speaks to the requirement for proper functioning of many processes in the cell. Retention of some clonality was seen in the closely-related SARA strains, with assortment of alleles more obvious across the more diverse SARB strains. Supported by evidence gathered here is the importance of horizontal gene transfer in evolution of selective benefits harbored by bacterial pathogens, in particular, S. enterica.Item ENHANCEMENT OF THERMAL INACTIVATION OF CRONOBACTER SAKAZAKII WITH INCLUSION OF PARABENS(2016) Ruan, Luxi; Buchanan, Robert L; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Parabens are a family of p-hydroxybenzoic acid esters, which have antimicrobial activity over a broad pH range (4-8). This study was designed to evaluate the enhanced thermal inactivation of Cronobacter sakazakii by the inclusion of “parabens” and to ultimately develop mathematical models to describe this effect. A heat-resistant strain, Cronobacter sakazakii 607, was heated at three mild heating temperatures in combination with treatments with five parabens in various concentrations. Results showed the presence of parabens significantly enhanced thermal inactivation in a concentration-dependent manner, and the effect increased with increasing alkyl chain length. The concentration of parabens, alkyl side chain length, and heating temperature acted synergistically, causing bacterial inactivation even at low temperatures that were not effective in killing C. sakazakii. The survival data were used to develop primary and secondary mathematical models that accurately describe how this synergistic activity can be applied in the food industry.Item ATTACHMENT, GROWTH AND PERSISTENCE OF CRONOBACTER ON GRANULAR ACTIVATED CARBON FILTERS(2016) Lu, Junchao; Buchanan, Robert L; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Several Cronobacter outbreaks have implicated contaminated drinking water. This study assessed the impact of granular activated carbon (GAC) on the microbial quality of the water produced. A simulated water filter system was installed by filling plastic columns with sterile GAC, followed by sterile water with a dilute nutrient flowing through the column at a steady rate. Carbon columns were inoculated with Cronobacter on the surface, and the effluent monitored for Cronobacter levels. During a second phase, commercial faucet filters were distributed to households for 4-month use. Used filters were backwashed with sterile peptone water, and analyzed for Cronobacter, total aerobic plate count, coliform bacteria and Enterobacteriaceae. Cronobacter colonized the simulated GAC and grew when provided minimal levels of nutrients. Backwashed used filters used in home settings yielded presumptive Escherichia coli, Pseudomonas and other waterborne bacteria. Presumptive Cronobacter strains were identified as negative through biochemical and genetic test.Item Antimicrobial Resistance of Salmonella and E. coli from Pennsylvania Dairy Herds(2015) Cao, Huilin; Pradhan, Abani K.; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The emergence and dissemination of bacterial antimicrobial resistance has become a major public health concern. A total of 444 manure composite samples were collected from 80 dairy farms in Pennsylvania, representing pre-weaned calves, post-weaned calves, dry cows, and lactating cows. E. coli and Salmonella were isolated, and tested for antimicrobial susceptibility. Salmonella was isolated from at least one sample from 51 (64%) farms and was more prevalent in adult animals than young animals. The predominant serotypes were Cerro, Montevideo and Kentucky. Salmonella isolates were mostly susceptible to all antimicrobials. E. coli were commonly resistant to tetracycline, streptomycin, sulfisoxazole and ampicillin. Resistance of up to 8 classes of antibiotics was observed in E. coli isolated from young animals. The blaCMY- and blaCTX-M-carrying E. coli were detected in 35% and 5% of the farms, respectively. The presence of multi-drug resistant E. coli suggested potential risks to human health associated with dairy farming.Item Investigating Metrics Proposed to Prevent the Harvest of Leafy Green Crops Contaminated by Floodwater(2015) Callahan, Mary Theresa; Buchanan, Robert L; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Pathogens can be transported by water through soil to contaminate distant crops. The California LGMA states that leafy green crops within 30ft of flooded soil should be destroyed due to potential contamination. Previously flooded areas should not be replanted for 60 days. This study investigated the transport of Salmonella enterica and Citrobacter freundii through soil in a model system with a positive slope (uphill). Field trials involving flooding one end of a spinach bed with a negative slope (downhill) with water containing Escherichia coli were also conducted. Soil type, soil moisture content, and slope affected bacterial movement. In field trials, E. coli was quickly transported to the 30ft boundary, and persisted significantly longer in the fall trial than the spring. These data suggest the LGMA metrics need to provide additional parameters to prevent the harvest of leafy green crops potentially contaminated by floodwater.Item ASSESSMENT OF PREHARVEST MICROBIAL QUALITY OF CANTALOUPES AND PUBLIC HEALTH RISKS ASSOCIATED WITH CANTALOUPES CONTAMINATED WITH LISTERIA MONOCYTOGENES(2014) Wang, Miao; Pradhan, Abani K; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cantaloupe has been recognized as a common vehicle for foodborne infections among fresh produce commodities. A severe multistate outbreak of Listeria monocytogenes associated with the consumption of whole cantaloupe resulted in 33 deaths in 2011. Quantitative microbial risk assessment (QMRA) modeling in food safety risk analysis has been acknowledged as an efficient tool to estimate and provide knowledge needed to manage potential public health risks associated with foodborne pathogens. The objectives of this study were to (i) conduct a microbiological survey of pre-harvest cantaloupes from farms in mid-Atlantic region, and (ii) develop a "farm to table" QMRA model for L. monocytogenes in cantaloupe. The results of the regional microbiological survey indicated a 5.3% (2/38) prevalence of generic Escherichia coli and negative for L. monocytogenes and Salmonella on cantaloupe during harvest season. A QMRA model was developed based on a thorough review of data from scientific publications and communications with fresh-cut processing industry. The model was simulated with Monte Carlo technique for 100,000 iterations in @Risk. The model estimated the public health risks associated with the consumption of both fresh-cut and whole cantaloupes in the U.S. The model demonstrated the risk associated with the consumption of a serving of fresh-cut cantaloupe is around 10 times higher than that for whole cantaloupe. Using the baseline model, the estimated median number of listeriosis cases per year associated with the consumption of fresh-cut cantaloupe among susceptible subpopulation and general healthy population are 0.0368 and 0.00134, respectively. Sensitivity analysis suggested temperature control during retail (correlation coefficient: 0.69) and home storage (correlation coefficient: 0.48) are two critical factors in mitigating the risk for fresh-cut cantaloupe consumption while home storage temperature (correlation coefficient: 0.79) after cutting is the most important factor for whole cantaloupe consumption. The QMRA model provided critical information for risk management and identified the critical data gaps including initial contamination and prevalence for future risk assessments of melon.Item ALTERNATIVE APPROACHES IN MOLECULAR CHARACTERIZATION OF FOODBORNE PATHOGENS: SHIGA TOXIN-PRODUCING Escherichia coli AND Salmonella SEROTYPES(2014) Toro Ibaceta, Magaly Alejandra; Meng, Jianghong; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Shiga toxin-producing E. coli (STEC) and Salmonella enterica subspecies enterica (S. enterica) are two major foodborne pathogens. They cause almost 1.5 million of cases of disease each year in the US. Due to their public health impact, development of new methods for their detection and identification are top priority. This research focused on identifying alternative molecular methods and markers for the identification of STEC and Salmonella. First, a suspension array was developed to simultaneously identify the seven most prevalent STEC (O26, O45, O103, O111, O121, O145, and O157) in the US. The panel targeted genes wzx or wzy and Shigatoxin genes. Testing and optimization employed four to eleven isolates of each serotype in the panel. STEC fluorescence values were 30 to >270 times greater than those of negative controls, demonstrating the method's effectiveness for the molecular serotyping of STEC. STEC strains (n=194) of 43 serotypes were examined for clustered regularly interspaced short palindromic repeats (CRISPR) arrays to study relatedness among serotypes. A subset of strains (n=81) was analyzed for cas and virulence genes to determine a possible relationship. CRISPR spacer content correlated well with serotypes, although some strains with different serogroup but the same H type shared identical arrays (O26:H11, O103:H11, and O111:H11). cas and virulence genes were not associated, but strains with greater probability of causing outbreaks and disease showed fewer spacers than those less likely to cause them (p<0.05). Therefore, CRISPR array content correlated well with STEC serotype, and CRISPR-cas systems were inversely related to strain virulence potential. Finally, the CRISPR arrays of 221 S. enterica of 53 serotypes were analyzed to define their relationship. CRISPR-cas systems of 50 S. enterica serotype Bareilly (S. Bareilly) were analyzed to resolve intra-serotype variations. CRISPR arrays correlated well with serotypes, although some serotypes displayed more than one type of array (e.g. S. Bareilly). Additionally, CRISPR-cas system elements reflected S. Bareilly phylogeny, but the array content was not linked to food vehicle or isolate's geographical origin. In conclusion, CRISPR array are useful for designing molecular serotyping assays, but a range of strains should be included to account for variation in S. enterica.Item Salmonella Newport: Genetic Diversity and Phylogenetic Analysis(2014) Cao, Guojie; Meng, Jianghong; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Salmonella enterica subsp. enterica causes over 99% of human salmonellosis. Salmonella Newport has ranked in the top three Salmonella serotypes associated with foodborne outbreaks in the United States. S. Newport is ubiquitous in the environment. S. Newport consisted of three lineages. It is necessary to investigate and determine the evolution relationship between S. Newport and to identify the genetic diversities of this emerging foodborne pathogen. Whole genome sequencing has played important roles in food safety and public health providing the most accurate information for phylogenetic analysis and more comprehensive picture for comparative genomics. Total 26 S. Newport strains from diverse sources and geographic locations were selected and conducted pyrosequencing to obtain 16-24 × coverage of draft genomes. More than 140,000 SNPs were identified to construct parsimony tree. Phylogenetic analysis indicated that S. Newport was divided into two major groups, lineages II and III. Lineage II was further grouped into three subgroups, IIA, IIB, and IIC. Lineage III strains showed close relationship to each other. Moreover, lineages II and III displayed divergent distance. Comparative genomics identified the region around mutS as potential biomarkers to distinguish these two lineages, including ste fimbrial operon, transposase, and cas genes. Salmonella pathogenicity islands (SPIs) play essential roles in virulence, metabolism, and host adaptations in Salmonella. Due to the significant roles of SPI-5 and SPI-6, the genetic diversities in these two gene clusters may contribute to the various activities in different strains. Both indels and mutations were identified in SPI-5, including two large insertions with over 40 kb encoding phage genes and 146 single nucleotide polymorphisms (SNPs). The phylogenetic tree of SPI-5 genes showed that lineages II and III contained divergent distances. SPI-6 was not identified in Asian strains in subgroup IIA, indicating the potential differences in virulence and host adaptations. S. Newport multidrug resistant strains have been clinical important issue in the United States. Plasmids contributed to the MDR phenotypes. The common genetic characterizations of these strains could be help to understand the prevalence of MDR strains. In the current study, all MDR strains belonging to one node in IIC and contained unfunctional CRISPR systems.Item Nutrition, Sensory, Quality and Safety Evaluation of A New Specialty Produce: Microgreens(2013) Xiao, Zhenlei; Wang, Qin; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microgreens are new emerging food products, which are young seedlings of vegetables and herbs, having two fully developed cotyledons with the first pair of true leaves emerging or partially expanded. They have gained popularity in upscale restaurants and grocery stores in recent years. However, little relevant scientific data is currently available on microgreens. The present research project was dedicated to explore the nutritional value, sensory attributes, consumer acceptance, postharvest quality and microbial safety of microgreens. In the first part of this project, phytonutrients were determined in 25 commercially available microgreens. Results showed that different microgreens provided extremely varying amounts of phytonutrients. Among the 25 microgreens assayed, red cabbage (Brassica oleracea L.), cilantro (Coriandrum sativum L.), garnet amaranth (Amaranthus hypochondriacus L.) and green daikon radish (Raphanus sativus L.) had the highest concentrations of ascorbic acids, carotenoids, phylloquinone, and tocopherols, respectively. Compared with the nutrient concentrations in mature leaves recorded in USDA National Nutrient Database, microgreen possessed higher nutrient density. Although microgrees are nutrient-dense, there is little information and data on the consumer acceptability of microgreens; therefore, consumer acceptance test were carried out. Six microgreens were first selected out of 25 varieties of microgreens in the prelimanry test and subsquently evaluated by 80 consumer panelists for sensory attributes. Chemical compositions and nutritional values of the taste-panel tested microgreens were also investigated for correlations with sensory attributes. All microgreens evaluated demonstrated "good" to "excellent" consumer acceptance and nutritional profil and overall acceptability of microgreens was significantly correlated with flavor acceptability. Generally, microgreens are very tender, and thus have a short shelf life. To optimize the postharvest handling conditions, the effects of temperature, modified atmosphere packaging (MAP) and chlorine wash on postharvest quality and shelf life of radish microgreens (Raphanus sativus L. var. longipinnatus) were studied. The impacts of light exposure during storage on sensorial quality and bioactive compounds were also investigated. Results showed that 1) one degree Celsius was the optimal temperature for radish microgreens storage; 2) MAP did not significantly affect quality attributes during 28 days of storage at 1°C; 3) chlorine wash treatment reduced microbial populations initially, however, it rebounded to pre chlorine wash levels within 7 days; and 4) light exposure accelerated quality deterioration and increased the amount of ascorbic acid, while dark storage may be profound for quality and carotenoid retention. The final part of this project was a comparative microbiological study between radish sprouts and radish microgreens producd from artificially contaminated radish seeds. Starting from seeds with same contamination levels, E. coli O157: H7 and E. coli O104: H4 populations on harvested radish microgreens were 3-4 logs lower than that on radish sprouts. These results demonstrated that the microbial growth on sprouts were much faster than that on microgreens, which poses great risk of microbiological hazard to sprout-consumers. In contrast, microgreens seem to bear a relatively low food safety risk.