College of Agriculture & Natural Resources
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Item SURVIVAL AND PERSISTENCE OF LISTERIA AND ESCHERICHIA COLI AND CHANGES IN PHYSICOCHEMICAL PARAMETERS IN AQUAPONICS SYSTEMS DURING LETTUCE PRODUCTION(2023) ALHAMMAD, GHADAH ABDULRAHMAN; Lei, David K. Y.; Nutrition; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aquaponic (AP) food production systems integrate aquaculture and hydroponics in soilless controlled environments while conserving space and natural resources (soil, water, air). Increasing global demand for high-quality quality nutritious, safe food continues to increase exponentially. Information specific to AP is needed to validate operational and handling practices for AP food safety. The first study is to assess the persistence of E. coli TVS 354 in bench-scale aquaponic systems (180 days after primary plant harvest). Methods: follow-up on the previous study and evaluate growth and persistence of E. coli TVS 354 at 180 days after primary plant harvest. Samples were collected from 10 independent aquaponic systems and bacterial growth was evaluated including aerobic plate count (APC), coliform bacteria (CB), heterotrophic plate count (HPC), and cultural enrichment for E. coli TVS 354 levels. Results: E. coli TVS 354 was not detected in samples from hydrotons (25 g), filters, fish feces, core and roots. The aerobic bacteria count of fish and plant tank samples ranged between 2.5 to 3 log CFU/mL for all treatments, while aerobic bacteria count on the core of the lettuce plant was significantly lower, ranging from 1.44 to 2.08 log CFU/mL. The second study is to evaluate the survival of Listeria innocua 2066 in effluent from fish tanks and plant tanks of aquaponic research units. Methods: four different treatments: fish tank water, fish tank water-replenished, plant tank water, and plant tank water-replenished. Each bottle was inoculated with Listeria innocua 2066, and bacterial growth and water chemistry conditions were evaluated over 7 days to identify physiochemical parameters associated with Listeria innocua 2066 survival and growth. Results: In 24 hours a significant reduction (p<0.05) in Listeria inccoua 2066 populations was observed for all treatments with a total reduction 3.9-3.7 log CFU/mL. Listeria innocua 2066 counts were lowest on day 7 for treatment groups, ranging from 1.1 log CFU/mL to 1.0 log CFU/mL. Treatments that were replenished daily from the aquaponic systems had higher counts of Listeria innocua 2066 compared to treatments that were non-replenished. The lowest APC on day 0, immediately after inoculation, ranged from 4.16 log CFU/mL to 4.32 log CFU/mL. A significant increase (P<0.05) in APC count was observed for all treatments in 24 hours while there is no significant difference in APC values between the treatments (p=0.35). The final and third study is to evaluate survival of inoculated Listeria innocua 2066 and nonpathogenic Escherichia coli and changes in AP physicochemical parameters. Methods: A four-week bench-scale AP experiment (n=12) with four goldfish (Carassius auratus)/aerated 37L tank, a 3-step biofilter, and four lettuce plants (Lactuca sativa var. Truchas)/37L hydroponic tank was conducted. Treatments were high and low-dose (6-log and 2-log CFU/mL, respectively) of Listeria innocua 2066-Er or E. coli-Rifr TVS 354, and uninoculated controls. Listeria innocua-2066-Er and E. coli-Rifr populations, mesophilic counts (APC), and physicochemical parameters (pH, temperature, dissolved oxygen, turbidity, ammonia, nitrite, and nitrate) were analyzed in plant tank water, and biofilters until plant harvest. Listeria innocua 2066-Er and E.coli-Rifr enumeration and APC (Petrifilm®) from lettuce shoots, roots and rockwool were determined at harvest. Results: Listeria innocua 2066 and E. coli TVS 354 populations declined significantly within 24 hours post-inoculation and were undetectable at day 14 and day 12 respectively (P <0.05). This decline was observed for both high and low-dose treatments. Listeria innocua 2066 and E. coli TVS 354 were detected in biofilters until week 4. At harvest, Listeria innocua 2066 and E. coli TVS 354 were recovered from lettuce roots, and rockwool, but not from plant leaves, and 100mL plant tank water grab samples. Lower leaves preharvest had a significantly higher APC (5.1- 6.4 log CFU/mL) relative to harvested lettuce upper leaves (2.8 - 4.2 log CFU/mL). Plant tank water pH had a significant effect (P<0.05) on Listeria innocua 2066 and E. coli TVS 354 survival. Significance: These results provide insights into the survival dynamics and sites of E. coli TVS 354 and Listeria innocua 2066 in AP and associated physicochemical conditions. These findings contribute to our understanding of potential food safety risks and associated risk factors such as inputs, physicochemical factors, and other environmental conditions in aquaponics systems.Item Enhancement of thermal processing with food-grade antimicrobial compounds in low-moisture food matrix to improve food safety(2022) Ding, Qiao; Tikekar, Rohan V; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Heat resistant foodborne pathogens have been a concern in low-moisture foods and ingredients (LMFs). Increased thermal resistance of pathogens such as Escherichia coli O157:H7 and Salmonella Typhimurium at low water activity (aw) reduces the efficiency of thermal treatment in LMFs. Alternative methods are therefore needed to augment thermal processing and reduce food safety risk. This study investigated the enhancement of thermal treatment efficiency against pathogenic bacteria in LMF matrices at different aw by inclusion of food-grade antimicrobial compounds. Based on their similar target sites in cells, it is hypothesized that antimicrobial compounds may work synergistically with heat treatment in LMF matrices. The treatment effect may be dependent on both aw and matrix compositions. Physiological and transcriptional changes may take place within cells adapted to different environments and contribute to the varied bacterial resistance. A combination of Butylparaben (BP), a known antimicrobial and thermal treatment was tested to enhance inactivation rates of S. Typhimurium and E. coli O157:H7 in meat and bone meal (MBM) equilibrated to water activity (aw) of 0.4 and 0.7. Presence of BP significantly accelerated thermal inactivation of E. coli O157:H7 in MBM at both 0.4 and 0.7 aw. However, inactivation rate of S. Typhimurium was not affected by the combined treatment at either 0.4 or 0.7 aw. BP accelerated the inactivation of the thermal-resistant subpopulation in E. coli O157:H7 but not S. Typhimurium. Therefore, further studies were conducted to identify alternative antimicrobial compounds to enhance thermal treatment against S. Typhimurium in LMF matrices and investigate the resistance mechanisms. Trans-cinnamaldehyde (CA) and eugenol (EG) were selected from a screening study to assist thermal treatment against S. Typhimurium adapted to different aw in whey protein (WP), corn starch (CS) or peanut oil (PO). Although addition of CA or EG significantly accelerated thermal inactivation of S. Typhimurium in water and LMF components at 0.9 aw, similar effect was not observed in bacteria adapted to lower (0.4) aw in any of those matrices. The matrix effect on bacterial thermal resistance was observed at 0.9 aw and were ranked as WP > PO > CS. The combined heat treatments reduced bacterial metabolic activity, which was partially dependent on the food components as well. S. Typhimurium had lower membrane fluidity because of membrane fatty acid composition change when adapted to a lower aw, which contributed to resistance against the combined heat treatments. Based on the aw- and matrix- dependent bacterial resistance and physiological changes observed in the two previous studies, transcriptional analysis was conducted to further understand the molecular mechanism behind the bacterial resistance. Expression of nine stress-related genes in S. Typhimurium adapted to different aw in LMF components were analyzed with or without the CA-assisted heat treatment. The upregulation of rpoH and dnaK in S. Typhimurium was induced by the stress during bacterial adaptation to the low aw environments as well as the combined heat treatment, which contributed to the bacterial resistance to both desiccation and the combined treatment. Although its link to the desiccation response in bacteria is not fully understood, the downregulation of ompC during the combined treatment also partially contributed to the treatment resistance. The upregulation of rpoE, otsB, proV and fadA in S. Typhimurium was induced by the desiccation stress during incubation at the low aw environment but was not a major contributor to the resistance during the combined treatment. The observed upregulation of fabA and downregulation of ibpA could not be directly linked to either bacterial resistance to desiccation or the combined heat treatment. Differential expressions were also observed among different aw levels or in different matrices at the same aw. The inconsistencies between the expression profiles of dnaK and ompC and bacterial resistance during the combined treatment suggested the presence of additional stress-response pathways.In conclusion, the results have demonstrated the potential of using food-grade antimicrobial compounds to complement thermal treatment in LMF during processes that start with a relatively high aw (such as dehydration). However, their effectiveness may subside at low aw environments. Future works should focus on optimizing the parameters of the CA/ EG-assisted heat treatment for higher efficiency, studying the molecular mechanism behind the bacterial resistance at global scale, and exploring alternative non-thermal processing technologies to enhance thermal treatment efficiency in LMFs without raising thermal treatment intensity.Item BIOACTIVE LACTOBACILLUS CASEI IN REDUCING GROWTH AND COLONIZATION OF CAMPYLOBACTER JEJUNI(2018) Tabashsum, Zajeba; Biswas, Debabrata; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Campylobacter jejuni (CJ) is one of the pre-dominant causative agents of acute gastroenteritis in the US and occurs commonly through handling/consumption of contaminated poultry products. Probiotics with enhanced bioactive metabolites such as conjugated linoleic acids (CLAs) play crucial role in improving host health and act as antimicrobials. Further, prebiotic like components such as bioactive phenolics from berry pomace extract (BPE) can stimulate growth of beneficial microbes including Lactobacillus casei (LC) and inhibit bacterial pathogens in vitro. In this study, we aimed to assess efficiency of CLA overproducing LC (LC+mcra) alone or in presence of BPE against CJ. LC+mcra alone or LC+mcra with BPE reduced CJ growth, adhesion and invasion efficiency to cultured cells and also altered physicochemical properties, gene expressions related to virulence. These findings suggest, BPE and LC+mcra in combination may able to prevent CJ colonization in poultry and reduce cross-contamination, hence control foodborne infections with CJ in human.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.Item Noninvasive Cleaning and Sanitation Monitoring System for Deli Department Processing(2013) Beck, Elizabeth Ann; Lo, Y. Martin; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The inability to adequately judge the efficacy of cleaning/sanitation in deli departments is a recognized food safety concern. In prior studies, our research group demonstrated that visual inspection of cleaned produce processing surfaces could be enhanced through the use of a portable imaging device. To explore the feasibility of using this technology to facilitate detection of deli residues, fluorescence spectra of deli commodities were acquired using a laboratory-based hyperspectral imaging system. Cheeses evidenced a strong response at 675 nm; meats were best detected at 475 or 520 nm, demonstrating these wavelengths are good candidates for deli residue detection. To confirm these findings, images were taken of an in-house deli slicer with the portable imaging device. Deli residues were detected and several slicer areas were identified as being prone to residue buildup. Results confirmed the potential to use a portable imaging device to enhance current cleaning procedures in a deli setting.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.Item FACTORS INFLUENCING MARYLAND FARMERS' ON-FARM PROCESSING LICENSE APPLICATION BEHAVIOR(2010) Lubran, Meryl; Kantor, Mark; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A 2005 regulation adopted by Maryland's state health department allowed farmers to sell foods processed in their home kitchen provided they complete an 8-hour food safety education course and apply for an on-farm processing license. Although more than 100 farmers completed the course, only 25 farmers applied for and received a license. The number of licenses granted has not met expectations and the health department is continually looking for ways to improve the program. The objective of this study was to identify factors that may influence Maryland farmers' intentions to apply for a license as well as their actual license application behavior using a model which combines two dominant theoretical paradigms - the Health Belief Model and the Theory of Planned Behavior. To test the proposed model, a mail survey was administered to farmers who completed the training, farmers who have an on-farm license, and to a systematic random sample of other Maryland farmers (n = 745). To explore reasons why the courses may not have encouraged more farmers to apply, a content analysis of the training presentations was conducted by two trained coders. The usable survey response rate was 15% (n = 110). Using structural equation modeling, the proposed model, predicting farmers' intentions to apply for a license, was found to have marginal fit. Significant direct relationships were found between farmers' attitudes, subjective norms, and their intentions. Significant indirect relationships were found between farmers' beliefs of perceived benefits and barriers and their attitudes. Using rare events logistic regression to predict license obtainment, and a multiple regression and two correlation analyses to test the proposed indirect relationships, the same relationships were found to predict actual behavior as behavioral intentions. An additional significant relationship was found between perceived behavioral control and behavior. Few differences were found between mean responses of farmers who did and did not attend the training. The content analysis of training materials revealed few persuasive strategies were utilized during training. These findings provide insight into factors affecting farmers' decisions to apply for an on-farm license, and suggest relevant factors, concerns, and issues to address in future educational outreach efforts.Item EPIDEMIOLOGY OF SALMONELLA CONTAMINATION OF POULTRY MEAT PRODUCTS: KNOWLEDGE GAPS IN THE FARM TO STORE PRODUCTS(2004-11-29) Myint, Maung San; Johnson, Yvette J; Veterinary Medical Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ultimate goal of controlling foodborne hazards is to reduce the risk of disease to consumers, and the economic burden related to foodborne illness. A literature review identified four areas of insufficient data on the epidemiology of Salmonella. A cross-sectional study was used to estimate prevalence of enteric bacterial contamination of plant-based animal feed and milk replacer from Maryland and Northern Virginia. All samples were negative for Campylobacter; 0.6% were positive for Salmonella; 5.7 % for E.coli; and 50.6% for Enterococcus. Samples purchased in summer of 2002 were 38 times more likely to be contaminated with Enterococcus than samples purchased in winter of 2002 (p-value<0.001). Enterococcus positive samples were 8 times more likely to be E.coli positive than Enterococcus negative samples. Another cross-sectional study was used to assess the association between the pattern of airflow and the distribution of fecal coliforms and Salmonella in commercial chicken litter. At moderate relative humidity (about 50%), there was a significant association between regions of reduced airflow and increased coliform and Salmonella contamination within a poultry house. An analysis of a PCR technique to validate sensitivity and specificity relative to culture techniques for detecting Salmonella contamination in retail poultry meat was conducted. When only BPW pre-enrichment was used, the PCR test had a sensitivity of 85%. This increased to 89 - 100% when BPW pre-enrichment was followed by selective enrichment with RV or TT-H broth, respectively when conventional culture is the gold standard. A minimum of 12 hours pre-enrichment and 100 cfu was necessary to achieve 100% sensitivity with PCR. Random poultry meat samples from 10 retail grocery outlets in Maryland were collected in the final cross-sectional study. Overall Salmonella prevalence in poultry meat products was 23% (C.I 15.16 - 30.86). Integrator brand ground chicken meat had an increased Salmonella prevalence compared to non-ground meat products; however this difference was not significant (p=0.0533). Store brand non-ground chicken meat products were 18 times more likely to be contaminated with Salmonella than integrator brands (C.I. 5.41-61.26).