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Title: COMPARATIVE ANALYSIS OF GROWTH KINETICS OF LISTERIA MONOCYTOGENES LINEAGES I AND II IN CHOPPED RED CABBAGE AND CUCUMBER USING PRIDICTIVE MODELING
Creator: Qi, Yan
Date: 2015, 2015-07
Description: Recently, outbreaks oflisteriosis assoc iated with cons umption of contaminated fresh produce by Listeria monocytogenes have increased....
Show moreRecently, outbreaks oflisteriosis assoc iated with cons umption of contaminated fresh produce by Listeria monocytogenes have increased. However, we know little about L. monocytogenes persistence and growth in fresh-cut produce items . The two main human foodbome outbreak lineages ofL. monocytogenes are LI and LB. Strains in LI (including serotypes 1/2b and 4b) are most likely to be isolated from human with listeriosis and Strains in LII (including serotypes 1/2a and 1/2c) are most likely to be isolated from food products and the natural environment. In order to determine the comparative survival and growth kinetics of these two lineages in chopped red cabbage and cucumber, samples of produce were chopped into 100 grams quantities and inoculated with 104 CFU/g of a cocktail of either LI (F2365, H7858, R2-502) or LII (LS814, JI-I 01, J1-067) antibiotic resistant strains. Samples were stored in deli-style containers at 5 or 10°C for 14 days, or 25°C for 7 days. At various intervals, samples were stomached and plated onto PCA with appropriate antibiotics. Data were modeled using DMFit from ComBase and statistical analyses were performed with GraphPad InStat. A p -value less than 0.05 was considered significant. The res ults for the grow th rates ((logIOCFU/g)/h) of the L. monocytogenes LI cocktail in red cabbage were significantly higher at 5°C (0.006±0.003), 10°C (0.017±0.004), and 25°C (0.051±0.017) than the LII cocktail ; and L. monocytogenes LI cocktail in cucumber were significantly lower at 25°C (0.098±0.00 84). Secondary models using the Ratkowsky equation presented r 2 values of 0.9866 for LI in red cabbage whereas presenting / values of 0.9998 and 0.9997 for LI and LII in cucumber, respectively. No significant difference between two lineages was seen in red cabbage and cucumber during ambient temperature display. Finally, the behavior of L. monocy togenes LI and LII on red cabbage and cucumber after potential consumer temperature abuse was determined. In red cabbage, LI grew steadily. However, the growth of L1I in red cabbage was more dynamic. In cucumber, there was no significant difference between LI and LII. The result s from this study will aid in comparing the growth and survival kinetics of Ll and L1l of L. monocytogenes and will provide guidance to both customers and the food industry.
M.S. in Food Safety and Technology, July 2015
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Title: LISTERIA MONOCYTOGENES SURVIVAL AND GROWTH IN FLAVORED MILKSHAKES MADE FROM NATURALLY-AND ARTIFICIALLY-CONTAMINATED ICE CREAM
Creator: Bathija, Vriddi Mahesh
Date: 2016, 2016-12
Description: Listeria monocytogenes is the causative agent of the disease listeriosis and was implicated in a multistate foodborne outbreak associated with...
Show moreListeria monocytogenes is the causative agent of the disease listeriosis and was implicated in a multistate foodborne outbreak associated with ice cream spread over four years from 2010 to 2014 in Kansas, Oklahoma, Texas and Arizona. Ten illnesses were reported during the course of this outbreak, resulting in 100% hospitalization and a mortality rate of 33%; the individuals who died in the outbreak had consumed milkshakes made with the contaminated ice cream. The ice cream was found to be contaminated uniformly at 10 MPN/g. This study assessed the growth kinetics of L. monocytogenes in milkshakes made with naturally- and artificially-contaminated ice cream, and with or without flavoring agents. Artificial-contamination of ice cream samples included inoculation with a cocktail of rifampicin-resistant L. monocytogenes into the middle of the product using a wide-orifice pipet tip. Milkshake were prepared with or without strawberry, chocolate, or mint flavoring, using the recipe associated with the healthcare facility where the illnesses occurred. Milkshakes were stored in sterile plastic cups at 10ºC and an asymmetric (3 tubes of 100ml, 5 tubes of 10 ml, 8 tubes of 1ml and 8 tubes of 0.1ml sampling scheme) most probable number (MPN) enumeration was conducted after 0, 12, 24, 48, 72, 96 and 144 h. The Baranyi model was used to model L. monocytogenes growth rates, maximum populations, and lag phases. Compared to milkshakes made with no flavoring agents, the milkshakes with flavoring resulted in decreased growth rates for L. monocytogenes for both contamination states; the lowest growth rate of the pathogen was observed in strawberry flavored milkshakes made from artificially-contaminated ice cream (0.029 log CFU/ml per hour). Chocolate and mint flavorings resulted in significantly (P < 0.05) longer lag phases for both natural (68.2 and 83.0 h) and artificial-contamination (47.7 and 54.2 h, respectively). The highest maximum population (5.79 log CFU/ml) was achieved by L. monocytogenes in naturallycontaminated milkshakes without any flavoring agent. Since challenge studies often depend on the artificial contamination of a food product, this study evaluated the differences between artificial and natural contamination of L. monocytogenes in milkshakes. The data obtained can be used for risk assessment purposes.
M.S. in Food Safety and Technology, December 2016
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Title: SURVIVAL OF LISTERIA MONOCYTOGENES AND ESCHERICHIA COLI O157:H7 DURING AGING OF GOUDA CHEESE MADE USING UNPASTEURIZED MILK
Creator: Natarajan, Vidya
Date: 2018, 2018-05
Description: The FDA code of federal regulations states that cheeses made using unpasteurized milk must be aged for a period of at least 60 days to...
Show moreThe FDA code of federal regulations states that cheeses made using unpasteurized milk must be aged for a period of at least 60 days to minimize the inherent risks associated with unpasteurized milk. However, there have been several foodborne outbreaks associated with 60-day aged semi-soft cheeses made using unpasteurized milk, specifically Gouda cheese. In this study, Gouda cheese was manufactured using unpasteurized milk artificially-inoculated with Listeria monocytogenes (1 or 3 log CFU/mL) and Escherichia coli O157:H7 (1 log CFU/mL). The Gouda cheese was pressed, brined, waxed, and aged at 10°C for 90 (for the 1 log CFU/mL) or 150 (for the 3 log CFU/mL) days. Samples were assessed during cheese manufacture and aging for survival of the pathogen as well as for the population dynamics of the native microflora including Enterobacteriaceae, yeast and mold, lactic acid bacteria, and mesophilic bacteria. In addition, cheese samples during aging were also analyzed for property characteristics including salt and moisture content, fat in solid content, pH, and water activity. Results determined that the population levels of both pathogens significantly increased during manufacture. During aging of the Gouda cheese, E. coli O157:H7 was capable of survival only until 49 days and was henceforth not detected via enrichment. For L. monocytogenes, pathogen populations were 2.07±0.12 log and 1.26±0.00 log CFU/g at 60 and 90 days of aging, respectively, for the 1 log CFU/mL initial inoculation level. Compared to day 60 (2.31±0.92 log CFU/g) of aging, the population of L. monocytogenes for the Gouda cheese made with the 3 log CFU/mL initial inoculation level was significantly higher (p<0.05) on both 90 and 150 d of aging (4.62±0.25 and 6.00±0.72 log CFU/g, respectively). During aging, the populations of lactic acid and mesophilic bacterial were significantly higher than other microflora categories. The population of yeast and mold displayed an increasing trend in population, whereas Enterobacteriaceae populations were highly unsteady. Increases in lactic acid bacterial populations were accompanied by decreases in pH and pathogen populations. These results indicate that the characteristics of Gouda cheese and the native microflora population may play a pivotal role in survival and growth of pathogens. Overall, this study suggests that the current 60-day aging regulation, while sufficient to control E. coli O157:H7, may not be suitable to control the risk of L. monocytogenes in Gouda cheese.The population of yeast and mold displayed an increasing trend in population, whereas Enterobacteriaceae populations were highly unsteady. Increases in lactic acid bacterial populations were accompanied by decreases in pH and pathogen populations. These results indicate that the characteristics of Gouda cheese and the native microflora population may play a pivotal role in survival and growth of pathogens. Overall, this study suggests that the current 60-day aging regulation, while sufficient to control E. coli O157:H7, may not be suitable to control the risk of L. monocytogenes in Gouda cheese.
M.S.in Food Safety and Technology, May 2018
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Title: GROWTH, SURVIVAL, AND INACTIVATION OF LISTERIA MONOCYTOGENES IN HUMMUS
Creator: Mhetras, Tanvi
Date: 2018, 2018-05
Description: Listeria monocytogenes is widely spread in the environment and is the causative agent of listeriosis. L. monocytogenes can contaminate ready...
Show moreListeria monocytogenes is widely spread in the environment and is the causative agent of listeriosis. L. monocytogenes can contaminate ready-to-eat (RTE) foods such as dairy products, salad dips, sandwiches, and seafood. In recent years, various recalls of hummus products have been reported to be associated with L. monocytogenes. This study aimed to 1) assess survival of L. monocytogenes on individual dry ingredients (chickpeas and sesame seeds), 2) examine survival of the pathogen in individual wet ingredients (mashed chickpeas and tahini) of hummus; 3) to evaluate L. monocytogenes survival in complete hummus dips; and 4) to determine L. monocytogenes inactivation in hummus dip using high pressure processing (HPP). Dry hummus ingredients (chickpeas and sesame seeds) were inoculated with a cocktail of four L. monocytogenes strains and stored at relative humidity (RH) levels of 25, 45, and 75% RH at 25 C for 28 d. When inoculated at 10 log CFU/g, L. monocytogenes populations decreased significantly (P<0.05) on sesame seeds and chickpeas in the first 24 h. The pathogen was more resistant to survival on sesame seeds at each of the RH levels than on chickpeas. The lowest D-value observed for L. monocytogenes was 9.90 d on chickpeas at 45% RH, while the highest value was 35.87 d on sesame seeds at 75% RH. When inoculated onto wet ingredients of hummus (mashed chickpeas and tahini), hummus dip, and hummus made using contaminated tahini or mashed chickpeas at 2 log CFU/g, L. monocytogenes was capable of survival in tahini during 28 d storage at 10 C. In mashed chickpeas, however, the pathogen increased significantly by approximately 4 log CFU/g after 7 d and had a growth rate of 2.21±1.34 log CFU/g/d. In hummus dip, L. monocytogenes had a significantly lower growth rate (0.11±0.01 log CFU/g/d) than in the mashed chickpeas. In hummus made using contaminated mashed chickpeas, the L. monocytogenes population significantly increased by 1.16 log CFU/g after 14 d. In hummus made using contaminated tahini, L. monocytogenes was capable of surviving, but did not grow. Hummus dip was treated with HPP at 350 MPa with holding times of 60,120,180 and 240 s. The D-value for L. monocytogenes was determined to be 98.2 seconds. The results from this study will aid in determining how L. monocytogenes survives in Refrigerated RTE hummus and its individual dry and wet ingredients. The study will also help in assessing the use of HPP for inactivation of L. monocytogenes in contaminated hummus.
M.S. in Food Safety and Technology, May 2018
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Title: CHARACTERIZATION OF NOVEL PULSED UV-LIGHT SYSTEMS FOR INACTIVATION OF LISTERIA MONOCYTOGENES IN APPLE JUICE AND ON APPLE SURFACE
Creator: Malik, Sargun
Date: 2018
Description: Pulsed light processing can effectively inactivate microorganisms from the surface of foods or in transparent liquid foods. Pulsed light...
Show morePulsed light processing can effectively inactivate microorganisms from the surface of foods or in transparent liquid foods. Pulsed light systems currently available in the market operate at a fixed pulse duration and frequency and might not be optimized for microbial inactivation. A novel pulsed light system (Model X 1100; Xenon Corporation, USA) enables the researchers to adjust various parameters including pulse duration (100-7000μsec), voltage(1000-3000V), frequency (0.1-20Hz),% of energy (0-100%), and energy (up to 9J /cm2 / pulse of optical energy or 2433J / pulse of electrical energy ) . This study evaluated the effect of various parameters (treatment time, voltage, frequency, energy / pulse) on inactivation of Listeria monocytogenes in buffered peptone water (BPW), apple juice, and apple surface. For liquids, a 4-mL of sample (4-mmdepth) artificially inoculated with Listeria monocytogenes was treated in a quartz Petri dish (5.5-cmdiameter). For solid food, the top surface (skin side) of a slice of apple (1×1×0.5cm）was inoculated and exposed to various pulsed light treatment conditions. The results indicated that the impact of these factors vary as many of these factors are inter-related. In general, increasing the frequency, input voltage, pulse duration, and percentage of energy, increased the microbial reduction at the tested conditions (p<0.05). For instance, reductions of 1.21and 5.47 log10 CFU/mL were obtained in BPW and reductions of 1.35 and 4.70 log10 CFU/mL was acquired in apple juice, at 0.1and 0.82Hz, respectively, for a 20-sec treatment at 2500V (50% energy,700 μsec pulse width). Increased energy per pulse resulted in increased microbial reduction. For example, reductions of 2.30, 5.59, 6.69, and 6.69 log10 CFU/mL were obtained at 645, 1241, 1837, and 2433J/ pulse of electrical energy, respectively, in apple juice. Similarly, reductions of 5.34, 6.45, 6.02, and 6.56 log10CFU/mL were obtained at 645, 1241, 1837, and 2433J/ pulse, respectively in BPW. Lower reduction was obtained from the skin surface of the apple, for instance, reductions of 0.70 and 1.19 log10 CFU/ slice were obtained at 0.10 and 0.82 Hz, respectively, after a 10 seconds treatment at 2500V (50%energy). Similarly, reductions of 2.44, 2.43, 3.39, and 3.48 log10 CFU/ slice were obtained at 645, 1241, 1837, and 2433J/ pulse of electrical energy, respectively, after a 15 seconds treatment at 3000V (0.2Hz). The results were similar to the pulsed light treatment with RC 800 system (Xenon Corporation, USA). Absorption of pulsed light energy resulted in temperature increase in the products. Temperature increase of up to 11°C was observed at the treated conditions. The results suggest that this novel pulsed light system can potentially be used for inactivation of Listeria monocytogenes.
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Title: Growth Kinetics of Listeria monocytogenes and Salmonella enterica on Rehydrated Enoki and Wood Ear Mushrooms during Storage
Creator: George, Josephina
Date: 2023
Description: Plant foods, such as fruits and vegetables, that have been dehydrated do not support the growth of pathogenic microorganisms. Recent...
Show morePlant foods, such as fruits and vegetables, that have been dehydrated do not support the growth of pathogenic microorganisms. Recent listeriosis and salmonellosis outbreaks in the U.S. have been associated with imported specialty mushrooms. These mushrooms are commonly sold fresh or dehydrated. This study evaluated the survival and growth of two foodborne pathogens Listeria. monocytogenes and Salmonella. enterica on dehydrated mushrooms during both rehydration at 25 or 5℃ and storage at 5, 10, or 25℃. Fresh enoki and wood ear mushrooms were dehydrated for 24 h at 60°C. Dehydrated mushrooms were inoculated with a four-strain cocktail of S. enterica or L. monocytogenes at 4 log CFU/g. Mushrooms were dried for 1 h, followed by rehydration for 2 h with 5 or 25°C (water and air temperature). Rehydrated mushrooms were stored at 5, 10, or 25°C for up to 14 d. The pathogens were enumerated at 0, 1, 3, 6, 9 and 14 d. Three independent trials with triplicate samples at each time point were completed. Population differences were evaluated via Student’s t-test; p<0.05 was considered significant. The growth rates were determined by DMFit in Excel. Overall, the growth rates of L. monocytogenes and S. enterica on enoki mushrooms were significantly higher when the mushrooms were rehydrated at 25℃ and stored at 25℃ (P<0.05). The growth rates were 2.69 log CFU/g per day and 3.56 log CFU/g per day, for L. monocytogenes and S. enterica respectively. Since the growth of pathogens on wood ear mushrooms during rehydration and storage was considerably less and below the level of enumeration, enrichment of the pathogens was conducted. The pathogens could be suppressed during rehydration due to less nutrient contents and antimicrobial properties of wood ear. The result of this study outlines the importance of refrigerated storage temperature and time combination for safety during rehydration and subsequent storage of the mushrooms.
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Title: Efficacy of Power Ultrasound Technology on the Reduction of Listeria monocytogenes and Salmonella enterica on Produce Matrices
Creator: Biswas, Priya
Date: 2023
Description: Fresh produces are considered as ready-to-eat (RTE) and are minimally processed before the distribution to retailers and consumers. Fresh...
Show moreFresh produces are considered as ready-to-eat (RTE) and are minimally processed before the distribution to retailers and consumers. Fresh produce recalls are frequently linked with pathogenic bacteria like Salmonella enterica and Listeria monocytogenes because of minimal processing. This study evaluated the use of power ultrasound coupled with organic acids like citric, acetic, and lactic acid which are generally recognized as safe and often helps to maintain the quality and prolong the shelf life of fresh RTE fruits and vegetables.All the produce matrices which include cucumbers, romaine lettuce, tomatoes, and strawberry were inoculated with four-strain cocktails of rifampicin-resistant S. enterica or L. monocytogenes at approximately 8 log CFU/ matrix. The produce matrices were dried for 1 h and treated for 2 minutes using 2 % or 5 % citric, lactic, or malic acid. This treatment was conducted with or without power ultrasound treatment at 40 kHz. Samples were taken in sets of three and placed into a stomacher bags. The bag contained 225 ml of water or acid. Following a 2 min treatment period, the samples were placed in separate stomacher bags, each containing 225ml of BPB or BLEB, for S. enterica or L. monocytogenes respectively. Followed serial dilutions, samples were then plated on BHIARif plates. For each condition, triplicate samples were taken, and three separate trials were conducted. The use of Student's t-test allowed for the evaluation of population differences, with a significance level of p<0.05 being deemed significant. Cucumber, romaine lettuce, tomatoes, and strawberries treated with 5 % concentration of citric, lactic, and malic acids, with addition of ultrasound showed a greater result in reductions of S. enterica to populations of 5.54 ± 0.47, 4.54 ± 0.83, and 4.69 ± x 0.36, log CFU/cucumber, 6.66 ± 0.51, 4.12 ± 0.32, and 5.51 ± 0.68, log CFU/ lettuce, 4.38 ± 0. 47, 3.12, and 5.04 ± 0.37 log CFU/ tomato, 4.66 ± 0.49, 4.69 ± 0.06, and 6.22 ± 0.39, log CFU/ strawberries, respectively. For L. monocytogenes, 5 % concentration of acids with the addition of ultrasound resulted in populations of 7.69 ± 0.35, 6.04 ± 0.24, and 6.96 ± 0.41, log CFU/ cucumbers, 7.57 ± 0.12, 5.49 ± 0.55, and 5.78 ± 0.73 log CFU/ lettuce, 6.44 ± 0.13, 5.08 ± 0.12, and 6.04 ± 0.22 log CFU/ tomato, 6.16 ± 0.37, 5.18 ± 0.22, and 5.64 ± 0.50, log CFU/ strawberries, respectively. The most effective acid was lactic when compared with citric and malic acids. The objective of this study is to investigate the effectiveness of power ultrasound as a novel non-thermal processing technology, in order to contribute to the existing knowledge base on this topic.
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Title: Factors Influencing the Level of Detection of Testing Listeria monocytogenes in Ice Cream
Creator: Chen, Bairu
Date: 2022
Description: The increasing evidence has shown that having a sensitive detection method for Listeria monocytogenes in food products is critical for public...
Show moreThe increasing evidence has shown that having a sensitive detection method for Listeria monocytogenes in food products is critical for public health as well as industrial economics. L. monocytogenes was associated with foodborne illness outbreaks linked to ice cream in the United States from 2010 to 2015, with another recent outbreak under investigation. The FDA Bacteriological Analytical Manual (BAM) method was commonly used for L. monocytogenes detection. However, the performance characteristics of the chromogenic methods (MOX, RLM, and R&F agars) remain to be elucidated. The factorial effect on Level of Detection (LOD) as an essential element of the International Organization for Standardization (ISO) approach for qualitative method validation was investigated in this study.For examining the LOD of L. monocytogenes in ice cream, fractional contaminated samples were prepared with the ice cream obtained from the 2015 outbreak and enumerated using the FDA BAM Most Probable Number (MPN) method for Listeria. The effect of test portion size was determined by comparing 10g and 25g using the BAM method with chromogenic agars (MOX, RLM, and R&F). The ISO single-lab validation requirement was followed for the factorial effect study, including four different factors: sample size (10g and 25g), ice cream types (commercially available regular vanilla ice cream and vanilla ice cream with low fat and no added sugar), re-freezing process (with re-freezing and without re-freezing process), and thawing process (slow thaw and fast thaw). LOD and relative LOD (RLOD) were computed using MiBiVal software to compare the sensitivity of the three chromogenic agars and the different factors. For all of the detection experiments, presumptive colonies were identified using the API listeria kit. The 2015 naturally contaminated ice cream was enumerated and resulted in an average contamination level of 2.15 MPN/g. At fractional levels of 0.25 MPN/10g and 0.75 MPN/10g, the positive rates of L. monocytogenes detected from 10g and 25g of sample portions were consistent with the statistically theoretical positive rates. The RLOD values for the reference method (MOX) and the alternative methods (RLM, R&F) were above 1 in both portion sizes, which suggested that MOX was slightly more sensitive than RLM and R&F. The factorial effect study indicated that the four factors have no significant influence on the LOD of L. monocytogenes detection at the fractional contamination levels. However, the test portion size of 25g provided more consistent results among the chromogenic media than the 10g portion size. Fat content was shown to have an effect on L. monocytogenes detection in a large test portion. The information from this study will be useful for the improvement of the reproducibility of a qualitative detection method and can also be used for data analysis standards such as ISO 16140 in method validation studies.
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