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PULSED LIGHT INACTIVATION OF MURINE NOROVIRUS ON VARIOUS FOOD CONTACT SURFACES
Title
PULSED LIGHT INACTIVATION OF MURINE NOROVIRUS ON VARIOUS FOOD CONTACT SURFACES
Creator
Zhou, Zijin
Date
2015, 2015-07
Description
Norovirus is one of the leading causes for foodborne illness. Transmission of virus from surface to food has been known to cause a number of...
Show moreNorovirus is one of the leading causes for foodborne illness. Transmission of virus from surface to food has been known to cause a number of outbreaks. Studies of norovirus have been conducted using Murine Norovirus to simulate the behaviors. Pulsed light (PL) is a promising surface decontamination technology, which has the potential to be applied in a food service setting. PL uses intense pulses of short duration and a broad spectrum to accomplish microbial inactivation. This study evaluates the effect of PL on MNV-1, artificially inoculated onto various food contact surfaces including 304 stainless steel, glazed tile, polypropylene, and ultra-high molecular weight (UHMW) polyethylene. The virus was allowed to inoculate on the coupons for 20mins and treated with PL in a Xenon Steripulse XL-3000TM pulsed light treatment system for up to 60 s, at a distance of 8.3 cm 10.8 cm or 13.3cm from the central axis of the lamp. An infrared (IR) camera was used to record surface temperatures, in 1-s increments. After PL treatments, remaining viruses were recovered from surfaces and quantified by plaque assay. At a distance of 10.8cm, MNV-1 was reduced by 2.22-, 2.27- 2.75- and 3.12-log, after 20s treatment on inoculated stainless steel, glazed tile, UHMW polyethylene and polypropylene, respectively. After 50s treatment, MNV-1 was reduced by 4.86- and 5.93- log on glazed tile and stainless steel surface respectively. The surface temperature on tile and stainless steel increased at the rate of 1.08±0.20 and 1.28±0.32°C /s respectively. A relatively short treatment using pulsed light is sufficient to inactivate MNV-1 on the surface of materials commonly used in food preparation. The results suggest that the technology has the potential to reduce surface viral contamination in a food preparation setting.
M.S. in Food Safety and Technology, July 2015
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DEVELOPING METHODS TO IDENTIFY SURROGATES FOR ESCHERICHIA COLI O157:H7 IN VALIDATION OF FRESH PRODUCE WASHING PROCESSES
Title
DEVELOPING METHODS TO IDENTIFY SURROGATES FOR ESCHERICHIA COLI O157:H7 IN VALIDATION OF FRESH PRODUCE WASHING PROCESSES
Creator
Rolfe, Catherine
Date
2016, 2016-07
Description
Cross-contamination during fresh produce washing is commonly prevented using chlorine treatment. Surrogate microorganisms have been widely...
Show moreCross-contamination during fresh produce washing is commonly prevented using chlorine treatment. Surrogate microorganisms have been widely used in process validation and to assess microbial cross-contamination. Fresh produce washing incorporates physical, chemical, biological and kinetic factors which create an intricate process for which little is known regarding surrogate selection. The purpose of this study was to identify the important elements relevant to produce washing processes and identify methods that will be used in surrogate selection. The behavior of three (3) non-pathogenic microorganisms (generic E. coli Nissle 1917 EcN, Pediococcus pentosaceus and lettuce isolate 813-F1) were examined in comparison to E. coli O157:H7 based on phenotypic similarities. Chlorine inactivation kinetics of E. coli O157:H7 and the non-pathogenic strains were evaluated with varying pH levels (6.5 and 8.0) and exposure times (3-30 seconds). Detachment of leaf-bound E. coli O157:H7 and non-pathogenic strains at different inoculation levels (approximately 2 and 6 log CFU/mL) and drying conditions (aging time, temperature) in wash water was examined. Chlorine inactivation at pH 6.5 resulted in a range of viability corresponding to E. coli O157:H7 and the non-pathogenic strains; demonstrating a sharp inactivation curve for E. coli O157:H7, EcN and P. pentosaceus. Whereas, inactivation at pH 8.0 allowed more survival relating to exposure time for all microorganisms. Detachment from inoculated leaves at 2 and 6 log CFU/mL inoculation showed steady survival levels in wash water at 0 ppm and lower survival at 1 ppm for all strains excluding 813-F1; 813-F1 was consistently less chlorine-sensitive in chlorine inactivation assays and more cross-contamination to wash water was observed for this strain. Aging time of inoculated bacteria on leaves was not seen to have remarkable effects on bacterial transfer during washing. These results suggest assay methods of chlorine inactivation at pH 6.5 and detachment with 6 log CFU/mL initial inoculation may be useful in selecting appropriate surrogates for fresh produce washing.
M.S. in Food Safety and Technology, July 2016
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GROWTH, SURVIVAL, AND INACTIVATION OF LISTERIA MONOCYTOGENES IN HUMMUS
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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