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Title: VALIDATION OF BAKING TO INACTIVATE SALMONELLA IN HIGH-PROTEIN AND HIGH-FAT MODEL FOODS
Creator: Wang, Wenqian
Date: 2017, 2017-07
Description: Baked food products, such as dry pet foods, undergo changes of temperature and water activity (aw) during forced hot air processes. As one of...
Show moreBaked food products, such as dry pet foods, undergo changes of temperature and water activity (aw) during forced hot air processes. As one of the most thermal resistant microorganisms in low-moisture/intermediate moisture foods, Salmonella’s thermal inactivation kinetics during these processes is not well understood and difficult to predict. The objective of this study was to evaluate thermal inactivation kinetics of Salmonella enterica serovar Agona 447967 in model high-protein (HP) and high-fat (HF) multiple-component foods baked in a laboratory-scale oven, as influenced by oven temperature and relative humidity (RH). Model high-protein and high-fat foods, formulated with wheat flour, soy protein and soy oil, were inoculated with Salmonella Agona to a level of ~9 log CFU/g, and mixed to form a homogenous dough. Dough samples (57 mm diameter x 6 mm thick) were baked (3 samples per dwell time, 6 dwell times per condition) in a lab-scale oven at 120°C (10% RH) and 85°C (20%, 35% RH, 50% RH), respectively. Temperature and aw were measured at the surface and geometric center of the product during baking. Processed samples were collected in sterile bags and immediately cooled in an ice-water bath. Salmonella was enumerated on trypticase soy agar supplemented with yeast extract and incubated at 37°C for 24 h. Similar reductions (p>0.05) of 5.12-, 5.11-, 4.55-, and 4.78-log CFU/g were achieved after 40 min at 120°C/10% RH, 90 min at 85°C/20% RH, 50 min at 85°C/35% RH, 8 min at 85°C/50% RH, respectively, in the high-protein model food. Similar results were achieved in the high-fat matrix. The aw at the geometric center of the product (initially at aw =0.98) did not change appreciably during baking, while the aw at the product surface, the location of least lethality, decreased significantly (p<0.05) during baking; the decreases were more pronounced at lower oven RH. The results indicate that thermal inactivation of Salmonella Agona was driven by temperature and relative humidity in the oven. Higher temperature and higher relative humidity level led to greater Salmonella inactivation.
M.S. in Food Process Engineering, July 2017
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Title: THERMAL STABILITY OF FOOD ALLERGENS AND NONALLERGENIC PROTEINS: A COMPARATIVE STUDY
Creator: Wu, Yan
Date: 2015, 2015-07
Description: Thermal stability has been proposed as a criterion to assess the allergenic potential of genetically modified foods, but there is a lack of...
Show moreThermal stability has been proposed as a criterion to assess the allergenic potential of genetically modified foods, but there is a lack of information on the relative thermal stability of food allergens vs. nonallergenic proteins. This study compared the thermal stability of several paired food allergens and nonallergenic proteins by measuring the changes in their solubility, antigenicity and thermodynamic properties after thermal treatment using BCA total protein assay, inhibition ELISA assay, Differential Scanning Calorimetry and Far-UV Circular Dichroism Spectroscopy. The selected protein pairs included bovine α-lactalbumin (allergen) vs. human α-lactalbumin (nonallergen), peanut lectin (allergen) vs. concanavalin A (nonallergen), soybean trypsin inhibitor (allergen) vs. lima bean trypsin inhibitor (nonallergen). With respect to protein solubility, a greater thermal stability was observed for: (1) bovine α-lactalbumin (bovine ALA) when it was autoclaved in water compared with human α-lactalbumin (human ALA) (2) peanut lectin when it was boiled or autoclaved in water compared with concanavalin A (ConA) and (3) soybean trypsin inhibitor (STI) when it was boiled in water or PBS, or autoclaved in water compared with lima bean trypsin inhibitor (LTI). Regarding TM values determined by DSC: (1) bovine ALA was more thermally stable than human ALA under both dry-heat treatment and moist-heat treatment (2) ConA was more thermally stable than peanut lectin during moist-heat treatment, while a greater thermal stability was observed for peanut lectin when the protein was under dry-heat treatment (3) LTI was more thermally stable than STI during heating in water or under dry-heat treatment, while a greater thermal stability was observed for STI when the protein was heated in PBS. Based on CD analyses, (1) bovine ALA was more thermally stable than human ALA (2) peanut lectin was more thermally stable than ConA (3) STI and LTI showed similar thermal stability. With respect to antigenicity, a greater thermal stability was observed for: (1) human ALA when it was autoclaved in water compared with bovine ALA (2) ConA when it was boiled or autoclaved in water, or under dry-heat treatment at 176℃ compared with peanut lectin (3) STI when it was autoclaved in PBS compared with LTI. In summary, allergens tended to be more thermally stable than nonallergenic proteins with respect to solubility, but there was no consistent trend in the relative thermal stability of these protein pairs regarding the antigenicity or the TM values. No correlation between thermal stability of the proteins and their allergenic potential was observed.ConA (3) STI and LTI showed similar thermal stability. With respect to antigenicity, a greater thermal stability was observed for: (1) human ALA when it was autoclaved in water compared with bovine ALA (2) ConA when it was boiled or autoclaved in water, or under dry-heat treatment at 176℃ compared with peanut lectin (3) STI when it was autoclaved in PBS compared with LTI. In summary, allergens tended to be more thermally stable than nonallergenic proteins with respect to solubility, but there was no consistent trend in the relative thermal stability of these protein pairs regarding the antigenicity or the TM values. No correlation between thermal stability of the proteins and their allergenic potential was observed.
M.S. in Food Safety and Technology, July 2015
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Title: FABRICATION, CHARACTERIZATION AND RELEASE STUDIES OF LOW DENSITY POLYETHYLENE/CLAY NANOCOMPOSITES
Creator: Zhao, Ziqian
Date: 2015, 2015-07
Description: Nanocomposites exhibit enhanced physical properties including mechanical strength, thermal stability, and gas barrier properties. The...
Show moreNanocomposites exhibit enhanced physical properties including mechanical strength, thermal stability, and gas barrier properties. The development of nanocomposites has led to applications in food industry, mostly in food packaging. The application of nanocomposites in food packaging may extend the shelf life of a food, thus increasing the market value for manufactures. However, there is limited data and research to assess the risk of exposure of nanomaterials to consumers. This project aims at evaluating the factors that can influence the release of nanomateirals in low density polyethylene/clay nanocomposites films. Nanocomposites based on low density polyethylene (LDPE), containing 1, 3, 5 and 7 wt.% of Cloisite 20A and maleic anhydride-grafted polyethylene (MAPE) as a compatibilizer were prepared by melt compounding and characterized in this thesis project. Cloisite 20A is mostly composed of montmorillonite (MMT), which is commonly used as a nanoscale size filler. LDPE/Clay nanocomposite films containing MMT and three mass equivalents of MAPE were successfully extruded into thin films with good optical clarity. The materials were characterized by using transmission electron microscope (TEM), thermogravimetric analysis (TGA), oxygen permeation analysis and a material testing machine. Important properties such as tensile modulus, oxygen transmission rate, thermal resistance and glass transition temperature were measured. Nanocomposite films were immersed in three kinds of food simulants (absolute ethanol, 3% acetic acid and deionized water). Storage time, storage temperature and percent fill of clay were evaluated as the factors that can influence the release of nanomaterials. The content of released of Al, Mg, and Si was quantified using inductively coupled plasma mass spectrometry (ICP-MS). Mg, Al and Si were continuously released from nanocomposite films in duration of 30 days. Fastest releasing speed was found in 3% aqueous acid at 75 °C, and lower temperature can largely decrease the release of nanoparticles. This project is an initial attempt to assess the risks from the use of nanocomposites as food packaging.
M.S. in Food Safety and Technology, July 2015
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Title: IN VITRO ASSAYS FOR ASSESSING THE IMPACT OF PROCESSING ON THE ALLERGENIC POTENTIAL OF MILK ALLERGENS
Creator: Zhao, Yuhui
Date: 2014, 2014-07
Description: A better understanding of how processing may affect the allergenicity of proteins will allow a more accurate allergen risk assessment and...
Show moreA better understanding of how processing may affect the allergenicity of proteins will allow a more accurate allergen risk assessment and achieve a greater success in food allergy management. To determine whether food processing can affect the allergenic potential of proteins, immunochemical methods are commonly used, however, these methods are not able to determine changes in the proteins’ ability to elicit allergic reactions. Although food challenge studies are the gold standard for determining the allergenicity of proteins, such studies are seldom performed due to ethical reasons and the difficulty in recruiting a sufficient number of study participants. In recent years, a number of mediator release assays have been developed to measure the allergenic potential of food proteins in vitro. How these cell-based assays can be used to assess the impact of thermal or other processing conditions on the allergenic potential of proteins remains to be determined. This study evaluated the use of sensitized rat basophilic leukemia (RBL) cells for assessing the impact of boiling on the allergenic potential of milk allergens by measuring changes in the proteins’ ability to induce cell degranulation and the release of β-hexosaminidase. RBL-2H3 cells sensitized with rat IgEs that were specifically raised against NIST non-fat milk standard reference material, β-lactoglobulin (BLG), α-lactalbumin (ALA) and α-casein (αCAS) were challenged with various concentrations of each allergen in its native and processed (boiled in PBS for 10 min) forms. Cell degranulation caused by the allergen was monitored by measuring the release of β-hexosaminidase. All allergens (NIST milk, BLG, ALA, and αCAS) were able to induce the release of β-hexosaminidase, up to 43.1%. A decrease in % release of β-hexosaminidase was observed when cells were challenged with a decreasing concenration xi of the ALA and milk allergens. Boiling of nonfat milk, ALA, BLG and αCAS caused an increase in the % release of β-hexosaminidase from sensitized cells across antigen concentrations from 10-6 mg/mL to 1 mg/mL. In conclusion, this study demonstrated that the in vitro mediator release assay method may serve as a useful model to evaluate the impact of thermal processing on the allergenic potential of milk allergens.
M.S. in Food Safety and Technology, July 2014
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Title: EFFECT OF HIGH PRESSURE PROCESSING ON MIGRATION CHARACTERISTICS IN POLYETHYLENE TEREPHTHALATE FILM
Creator: Zhou, Yue
Date: 2015, 2015-12
Description: High pressure processing (HPP) is gaining prominence worldwide as an alternative method of food preservation due to its benefits of improved...
Show moreHigh pressure processing (HPP) is gaining prominence worldwide as an alternative method of food preservation due to its benefits of improved quality, freshness and nutrient retention. The use of polymer-based flexible packaging materials has allowed application of HPP to prepackaged food products, without significant loss of physical and mechanical properties. However, there is limited data existing on migration properties in the materials before and/or after HPP. Therefore, it is necessary to evaluate potential migration issues in pre-packed foods during HPP (Song 2014). This research was conducted to determine the migration properties in polyethylene terephthalate (PET) films during and after HPP (121°C and 700MPa) and a comparable thermal processing (TP, 121°C and 0.1MPa), using gas chromatography (GC) coupled with mass spectrometer (MS) technique to quantify four model surrogates in FDA-suggested food simulants (Miglyol). This research will help the U.S Food and Drug Administration (FDA) and food industries to identify whether any safety issue related to chemical migration should be addressed concerning the use of HPP in production of pre-packaged foods.
M.S. in Food Safety and Technology, December 2015
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Title: DEVELOPMENT AND VALIDATION OF A HIGH PERFORMANCE LIQUID CHROMATOGRAPHIC METHOD FOR SIMULTANEOUS DETERMINATION OF VITAMINS A AND D IN FLUID MILK PRODUCTS
Creator: Li, Wenjing
Date: 2013, 2013-12
Description: Measurement of fortification levels for vitamins A and D in fluid milk products is required by the U.S. Food and Drug Administration (FDA)...
Show moreMeasurement of fortification levels for vitamins A and D in fluid milk products is required by the U.S. Food and Drug Administration (FDA) according to Pasteurized Milk Ordinance. In the current study, a high performance liquid chromatographic (HPLC) method was developed for simultaneous determination of retinyl palmitate (vitamin A) and cholecalciferol (vitamin D3) in fortified milk, which will enhance the efficiency of routine monitoring of fortification for processors as well as laboratories. Saponification conditions and extraction solution compositions were studies for best recovery and simplification of the extraction procedures. Saponification conditions studied included temperature (20, 40 and 60℃), time (0.5 to 16 hour) and concentration of KOH (20, 30, 40 and 50%). The variables studied for extraction included solvent compositions (hexane, diethyl ether, ethyl acetate and dichloromethane) and corresponding polarities (0.1, 0.25, 0.5 and 0.75), and number of extractions (once, twice and three times). Freezing and centrifuging steps were also investigated to compare to SPE clean-up, as an alternative method to clean-up before injection. The optimum parameters found were: saponification conditions at 60℃ for 2 hours with 40% (w/v) KOH liquid-liquid extraction with hexane: diethyl ether (80:20, v:v). Vitamins A and D3 were quantitated using an HPLC system with fluorescence detector (FLD) and diode array detector (DAD) respectively within the same injection. Spike recoveries from three different fat levels (skim, 2% and whole) of commercial pasteurized milk samples were in the range of 94 to 110% for both vitamins A and D3 at three spike concentration levels. In addition, at National Institute of Standards and Technology (NIST) Standard Reference Material (SRM 1849a) was used xii for method accuracy evaluation. With eight replicates, the average vitamin A (expressed as retinol equivalents) concentration was 7.52 ± 0.23 μg/g, vitamin D3 concentration was 0.114 ± 0.0062 μg/g, an excellent agreement with the certified value of 7.68 ± 0.23 μg/g for vitamin A and 0.11 ± 0.017 μg/g for vitamin D3. In summary, an HPLC method for simultaneous determination of vitamins A and D3 in fluid milk products has been developed. The method showed high efficiency and accuracy of analysis during a single laboratory validation.
M.S. in Food Safety and Technology, December 2013
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Title: MINIMIZING SALMONELLA CONTAMINATION IN SPROUTS BY CONTROLLING THE GERMINATION TEMPERATURE
Creator: Zhang, Hanshuai
Date: 2013, 2013-12
Description: Since 1990, contaminated sprouts have been linked to at least 46 outbreaks and over 2,500 cases of illness in the US [13]. Unlike other ready...
Show moreSince 1990, contaminated sprouts have been linked to at least 46 outbreaks and over 2,500 cases of illness in the US [13]. Unlike other ready-to-eat produce, sprouts pose a particular concern as the conditions that promote germination of their seeds also facilitate the growth of pathogens [6]. To address sprout’s propensity to microbial contamination, the U.S. Food and Drug Administration (FDA) has recommended that seeds destined for sprout production be disinfected with chemical sanitizers such as 20,000 ppm of calcium hypochlorite, Ca(OCl)2 [29]. However, this disinfectant often cannot completely eliminate pathogen that may be present in seeds [4, 23]; in which case, the surviving bacteria can re-grow to significant numbers during germination and cause severe illness upon consumption [45]. Therefore, maintaining control of the germination conditions to present the proliferation of pathogens is a crucial step in the overall approach to reduce microbial hazards in finished sprouts. This study examines the effects of temperature on the proliferation of Salmonella during germination, and how this temperature effect is influenced by factors such as pathogen load, seed-lot, and the presence or absence of chemical treatment with Ca(OCl)2 was also evaluated. Alfalfa seeds artificially inoculated with ~3 log CFU/g of Salmonella were used as the contaminated seeds. They were mixed at different levels (0.01, 0.1, 1.0, or 10.0% by weight) with 200g of non-contaminated seeds and then were allowed to germinate in glass jars for 3 or 5 days at 10, 20, or 30°C. The same experiment was repeated for the spiking seeds that were treated with 20,000 ppm Ca(ClO)2 for 15 min prior to sprouting. Sprout samples were taken from each jar daily and analyzed for the level of Salmonella ix by either plating on XLD plates or the three-tube most probable number method as described in the FDA BAM. The level of Salmonella increased during sprouting at all three temperatures and reached the highest level at 48h. Sprouting at 10°C yielded the least number of Salmonella when all other factors were controlled. At all spiking levels, or the percentage of seeds contaminated before sprouting, level of Salmonella increased during sprouting, and at 20°C and 30°C, the level of Salmonella reached to a similar level of 5 log CFU/g and 7 log CFU/g respectively. At 1.0% spiking level, the level of Salmonella increased by approximately 1.5, 4.0, and 6.0 log CFU/g in sprouts grown at 10, 20, and 30°C respectively. Difference in the level of microflora background between different seed lots did not appear to affect Salmonella proliferation during sprouting. Treatments with 20,000 ppm free chlorine in some cases lowered the levels of Salmonella to undetectable levels, while in other cases, it caused an approx. 3 log reduction in Salmonella count on seeds. The surviving ones could still proliferate during sprouting although with a delay and a much slower rate, and did not reach the maximal level at 48 h of sprouting. However, Ca(OCl)2 did not prevent the re-growth of Salmonella during germination. In conclusion, these results showed that sprouting temperatures do affect Salmonella proliferations. We recommend lowering the sprouting temperature in conjunction with chemical treatment of prior to sprouting seeds to reduce microbial hazards in sprouts.
M.S. in Food Safety and Technology, December 2013
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Title: FEASIBILITY OF INDICATOR MICROORGANISMS IN ASSESSING THE EFFICACY OF SANITIZERS IN FRESH PRODUCE WASHING
Creator: Zhong, Zeyan
Date: 2016, 2016-05
Description: Sanitizers have been widely used in controlling cross-contamination during fresh produce washing processes. It is important to identify...
Show moreSanitizers have been widely used in controlling cross-contamination during fresh produce washing processes. It is important to identify different approaches for monitoring the efficacy of sanitizer washing. In this study, our objective was to determine the feasibility of indicator microorganisms in assessing the efficacy of chlorine and peroxyacetic acid (PAA) in fresh-cut produce washing. In inactivation experiments, the survivals of inoculated indicator microorganisms [total viable count (TVC), Enterobacteriaceae and total coliforms] and E. coli O157:H7 were determined after exposure to different concentrations of chlorine or PAA in water with added organic load (TOC~200 mg/l). In small-scale washing experiments, bacterial transfer from lettuce leaves inoculated with indicators or E. coli O157:H7 to wash water containing chlorine or PAA with/without organic matters was evaluated. In the inactivation study, higher log reduction was observed for Enterobacteriaceae and total coliforms than for E. coli O157:H7 after chlorine treatment at an initial concentration of 30 ppm. In the bacterial transfer study [a inoculated leaf (~5 log CFU) in 30 ml of wash water], without additional organic matter, approximately 3.5 log total CFU of all bacteria groups was transferred into wash water. Less than 1.5 log total CFU were detected for Enterobacteriaceae, total coliforms and E. coli O157:H7 in 1 ppm chlorine washing. With introduced organic matter, similar microbial loads of Enterobacteriaceae, total coliforms and E. coli O157:H7 were detected on washed leaves and in wash water with initial chlorine concentration of 1 ppm; when initial chlorine level increased to 10 ppm, less than 2 log total CFU of Enterobacteriaceae and total coliforms was detected while about 3 log total CFU of E. coli O157:H7 transferred to wash water, suggesting that chlorine at an initial concentration of 10 ppm could not prevent cross-contamination in the presence of organic load. The indicators showed different levels of survival and transfer from E. coli O157:H7 in this study and were unreliable to effectively monitor the behavior of the pathogen during chlorine wash in fresh produce processes. Enterobacteriaceae and total coliforms were more vulnerable to 40 ppm PAA treatment than E. coli O157:H7 in PAA inactivation experiments. No survival, except for TVC, was observed after 80 ppm of PAA inactivation. In the bacterial transfer study, 40 ppm PAA in wash water was found unable to prevent cross-contamination of indicators and E. coli O157:H7 from leaves to water. Further investigation is needed to compare the bacterial transfer levels of E. coli O157:H7 and the indicators at higher PAA levels.
M.S. in Food Safety and Technology, May 2016
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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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Title: STUDY OF SALMONELLA SURVIVAL ON THE SURFACE OF FRUITS
Creator: Sui, Ke
Date: 2017, 2017-05
Description: Salmonella enterica has been frequently linked to the major foodborne disease outbreaks. The molecular mechanisms underlying this pathogen...
Show moreSalmonella enterica has been frequently linked to the major foodborne disease outbreaks. The molecular mechanisms underlying this pathogen survival on the fresh fruit surface remain largely unexplored. In this study, the environmental factors that affect the survival of Salmonella strains on the surface of selected fruits were studied. Grape tomatoes (or cantaloupe peels) were inoculated in three separate trials with 1 mL Salmonella enterica serotypes Enteritidis or Typhimurium (approximately 1010-11 CFU/mL). Storage of grape tomatoes at 4 ℃ resulted in significant decrease in populations of S. Enteritidis; this trend was observed at both of the tested relative humidity with the D-value as 7.25±1.05 d and 7.28±2.34 d, respectively. At different temperatures, relative humidity only had marginal effects on the bacterial survival on the surface of grape tomato and cantaloupe. In addition, S. Typhimurium apparently survived better than S. Enteritidis on the surface of grape tomato. Furthermore, a transposonmutagenesis library with random transposon insertion mutants of S. Enteritidis and high-throughput sequencing analysis showed that the expression of genes rcsB and nlpD were hypothesized to be associated with the survival of S. Enteritidis on grape tomatoes. Inframe deletions of the two genes in S. Enteritidis were constructed by lambda red recombinase system and respective complementation mutants were also obtained for identification of the contribution of the two genes to the bacterial survival on the surface of grape tomato. Thus, this study provided microbiological and molecular microbiological basis to probe the roles of putative genes in Salmonella enterica survival on the surface of fresh fruits.
M.S. in Food Safety and Technology, May 2017
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Title: FABRICATION OF POLYMER OF CLAY NANOCOMPOSITES AND DEVELOPMENT OF CLAY DIGESTION METHODS
Creator: Jin, Zhen
Date: 2014, 2014-07
Description: This thesis reports on our preliminary development of methods used to assess the risks that polymer/clay nanocomposite (PCN) food packaging...
Show moreThis thesis reports on our preliminary development of methods used to assess the risks that polymer/clay nanocomposite (PCN) food packaging pose to consumers. PCN with 1% - 7% (w/w) montmorillonite (MMT) clay and 3 mass equivalents of maleic anhydride-grafted polyethylene (MAPE) as a compatibilizer dispersed in low-density polyethylene (LDPE) was successfully extruded into thin, free-standing films using a pilot-scaled microcompounder with 65 mm film device. These films had good optical clarity and a reasonably consistent thickness of 35 ± 3 μm. An oxygen permeability analyzer was used to measure oxygen transmission rate and permeability of these fabricated films to demonstrate that they perform similarly to PCN barrier materials intended for commercial applications; these results showed that the films with the highest amount of added clay had better barrier properties than the neat LDPE films. In preparation of experiments to assess whether clay particles can be released from these materials during intended conditions of use, we also explored effective digestion and trace-metal analysis (Inductively Coupled Plasma-Optical Emission Spectroscopy) methods of both pure clay and MMT/MAPE/LDPE films. This work resulted in an effective digestion protocol to fully digest neat clays and PCN films, as well as an analysis method that provides for a 5-orders-of-magnitude linear detection range and single-digit parts-per-billion detection limits for aluminum and magnesium. Silicon was a more challenging element and efforts to eliminate environmental contamination of samples with this element were unsuccessful. While the work presented in this thesis is largely preliminary and numerous questions remain unanswered, the PCN fabrication and ix characterization methods developed here will be invaluable in our future efforts to understand the risks that nanocomposite food packaging materials pose to human health.
M.S. in Food Process Engineering, July 2014
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Title: IMPACT OF INOCULUM LEVEL ON THE TRANSFER OF SALMONELLA SEROVARS FROM CONTAMINATED ALMOND BUTTER TO FOOD CONTACT MATERIALS
Creator: Zheng, Yue
Date: 2012-11-19, 2012-12
Description: Outbreaks of salmonellosis associated with nut butter have raised public concerns of sanitation issues in nut butter processing. The high fat,...
Show moreOutbreaks of salmonellosis associated with nut butter have raised public concerns of sanitation issues in nut butter processing. The high fat, low-moisture characteristics of nut butters significantly affect the efficiency of regular cleaning and sanitizing programs, allowing cross-contamination issues to persist on processing equipment. Besides organic matter in food soil, microbial load could also be a factor affecting efficacy of chemical sanitizers. The FDA Food Code (2005) require a 5-log bacterial reduction in testing the efficacy of a chemical sanitation method. As a result, evaluation of microbial transfer is essential for establishing methods for equipment sanitation. The first study of this thesis (Section 4.1) evaluated the survival of Salmonella serovars in almond butter at 25 ± 2 oC. This was achieved by investigating the survival of Salmonella Tennessee and Salmonella Oranienburg in inoculated almond butter sample for up to two weeks. These Salmonella serovars were inoculated into creamy almond butter separately and stored at 25 ± 2 oC. Results showed that Salmonella populations decreased slowly and could survive in almond butter for at least two weeks. This study also investigated the effect of initial inoculum level, contact time, food-contact material and bacterial serovar on the subsequent potential for transfer of bacteria to equipment surfaces (Section 4.2). Almond butter inoculated with Salmonella Oranienburg and Tennessee at different inoculums levels (~3, 6, 9 log CFU/g) were spread on 16 cm2 coupons made of polyethylene, polyurethane, Delrin and stainless steel. Microbial analysis was conducted after physically removing all visible nut butter with laboratory wipes. Results for S. Oranienburg and Tennessee followed similar trends of microbial transfer with regards to inoculum level and food-contact surface. The amount x of Salmonella transferred to a food-contact surface was dependent on initial inoculation levels. An average of 0.88 ± 0.22, 1.53 ± 0.15, and 4.59 ± 0.06 log CFU S. Tennessee per 16 cm2 were transferred to the four different food-contact surface types for low, medium, and high inoculum level, respectively. An average of 1.25 ± 0.24, 2.08 ± 0.08, and 4.55 ± 0.35 log CFU S. Oranienburg per 16 cm2 were transferred to the same four different foodcontact surfaces for low, medium, and high inoculum levels, respectively. The third part of this study (Section 4.3) determined the transfer of Salmonella from contaminated food-contact coupon surfaces to almond butter. Uninoculated almond butter was applied on the surface of previously contaminated food-contact coupon surfaces. More than 5 log CFU/16 cm2 Salmonella could transfer to clean almond butter after immediate contact (within 5 min) with the contaminated area. These findings help advance our understanding of factors affecting microbial transfer between nut butters and processing equipment surfaces. This research can be used to support future cleaning and sanitation studies for nut butter processing equipment.
M.S. in Food Safety and Technology, December 2012
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Title: SURVIVAL AND GROWTH OF LISTERIA MONOCYTOGENES IN CHOPPED GREEN AND RED BELL PEPPERS USING PREDICTIVE MODELING
Creator: Zhang, L1jie
Date: 2015, 2015-07
Description: Listeria monocytogenes (L. monocytogenes) is a Gram-positive pathogenic organism and the causative agent of human and animal listeriosis....
Show moreListeria monocytogenes (L. monocytogenes) is a Gram-positive pathogenic organism and the causative agent of human and animal listeriosis. Listeriosis is a gastrointestinal or invasive systemic illness resulting from consumption of contaminated food products, mainly cheese, deli meats, and fresh produce, by L. monocytogenes. In recent years, several foodborne outbreaks have been reported that were associated with fresh produce, such as cantaloupe, celery and sprouts. Temperature is considered a major factor that affects L. monocytogenes growth during storage. The proliferation of L. monocytogenes varies on different produce items based on storage temperature. In this study, the persistence and population dynamics of three L. monocytogenes strains, LS806 (cheese isolate), LS810 (cantaloupe isolate) and LS808 (celery isolate) were evaluated by incubating inoculated fresh-cut green bell pepper and red bell pepper at various temperatures (5oC, 10oC, and 25oC) for 14 days. To assess the risk of L. monocytogenes in these fresh-cut vegetable items, a primary predictive model was fitted for L. monocytogenes growth data using DMFit. Green bell pepper had significantly (P<0.05) higher pH and aw, and higher amounts of yeast and mold and Enterobacteriaceae than did red bell pepper. In green bell pepper, all three strains showed no significant difference (P>0.05) in growth rate when incubated at the same temperature. In red bell peppers, LS808 had the highest (P<0.05) growth rate at both 5°C and 25°C out of the three strains. All of the three strains grew significantly faster (P<0.01) at 25°C than either 5°C or 10°C in both green and red bell peppers. All three strains obtained less than 1 log10 growth increase after incubating at 25°C for 6 hours on pre-chilled produce. Some strains (LS806 and LS810) significantly increased (P<0.01) during two 5-hour 25°C incubations, but did not reach 1 log10 growth increase. The results indicate that L. monocytogenes not only persists, but also grows in chopped green and red bell peppers at 5, 10, and 25°C, and strains grew faster at the higher temperature (25°C). Data obtained could be further evaluated for determining whether Time/temperature control for safety (TCS) designation should be applied to chopped green and red bell peppers.
M.S. in Food Safety and Technology, July 2015
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Title: THERMAL PROCESSING TO MITIGATE ARSENIC CONTENT IN NORTH AMERICAN RICE: TOTAL, SPECIATED ARSENIC AND NUTRIENT EVALUATION
Creator: Zhao, Pengyi
Date: 2015, 2015-05
Description: Arsenic in the food supply has been a concern since public news reports in 2011 of the detection of arsenic in apple juice. Food and Drug...
Show moreArsenic in the food supply has been a concern since public news reports in 2011 of the detection of arsenic in apple juice. Food and Drug Administration (FDA) work on this issue has proposed a guidance for no more than 10 ppb of inorganic arsenic in apple juice. More recently rice harvested from the southern states of the United States is of concern of the arsenic content. Arsenic levels in rice have been attributed to the natural levels of arsenic in the soil and the farming practices used to grow rice. FDA released data that showed inorganic arsenic amounts in long grain white rice between 70 and 150 ppb. This work presents a process through washing/ rinsing to reduce the arsenic levels in prepared/cooked rice. Four different rice materials were obtained from Mississippi, Arkansas, Texas and Louisiana. Different processing methods such as common cooking, washing and cooking, excess water cooking, were used to prepare the rice. The common cooking method cooked the rice in a 2:1 (water : rice) ratio. The washing and cooking method rinsed a batch of rice with a 2:1 (water : rice) ratio at first, and then poured off wash water and added new water to cook rice in a 2:1 (water : rice) ratio. The excess water cooking method cooked the rice in excess water of a ratio of 4:1 (water : rice) and the excess water was removed after cooking. Controls of raw rice samples were also evaluated. The common cooked rice showed variable to no difference (-13.9% to 14.9%) from the raw control in arsenic retention. The washed and cooked rice showed a 9.8% to 36.8% reduction of arsenic from the control. The excess water cooked rice showed the greatest reduction of arsenic from 39.1% to 65.5% compared to the control. The species of arsenic mimic the total arsenic loss. There is a visible trend for reduction of arsenic content by washing, but the most reduction was achieved by cooking rice with an excess volume of water.
M.S. in Food Safety and Technology, May 2015
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Title: APPROACHES TO QUANTIFY AND COMPARE THE THERMAL STABILITY OF FOOD ALLERGENS
Creator: Meng Xu
Date: 2013-04-24, 2013-05
Description: Stability to heat or other food processing conditions has been suggested as one of the characteristics of food allergens, however there is in...
Show moreStability to heat or other food processing conditions has been suggested as one of the characteristics of food allergens, however there is in general a lack of standardized approach to determine or compare the thermal stabilities of food allergens. This study evaluated the use of several analytical tools including the BCA total protein assay, Far-UV Circular Dichroism Spectroscopy, Differential Scanning Calorimetry, and inhibition ELISA assays to study the changes in the structural and immunological properties of major allergens as a result of heat treatments, and identified parameters that can be used to quantify and compare the thermal stability of food allergens. Purified allergens from milk, egg, and almond were subjected to moist-heat or dry-heat treatments and changes in protein solubility, IC50 values and thermodynamic properties of each protein were determined. It was found that high transition temperature (Tm) was closely related to a greater resistance to changes in immunological properties after heat treatments, suggesting that it can be a good parameter to quantify and compare the thermal stability of different food allergens.
M.S. in Food Safety and Technology, May 2013
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Title: TRANSFER RATE OF NOROVIRUS DURING CHOPPING ROMAINE LETTUCE
Creator: Li, Mingming
Date: 2012-11-24, 2012-12
Description: Human noroviruses (HuNoV) are the leading cause of outbreaks of nonbacterial gastroenteritis in the U.S., and are often implicated in...
Show moreHuman noroviruses (HuNoV) are the leading cause of outbreaks of nonbacterial gastroenteritis in the U.S., and are often implicated in outbreaks associated with ready-to-eat foods, such as salads. Such foods may be extensively handled, and norovirus may be transferred readily between infected food handlers and food surfaces. The aim of this study was to investigate norovirus transfer between surfaces and romaine lettuce which were commonly used in the preparation of fresh food. Fresh Romaine lettuce was cut into 25cm2 pieces and inoculated with 25 μl (approx. 7-log PFU) murine norovirus (MNV-1) per leaf. After 10 min air-drying, 5 g piles of inoculated leaves were cut with a sterile stainless steel knife on a sterile cutting board. Sampling sponges soaked in Dulbecco’s Modified Eagle’s Media (DMEM) were used to swab blade and board surfaces for MNV-1 transferred from lettuce. In some cases, fresh, uninoculated Romaine lettuce was chopped using the contaminated knife and board. MNV-1 transferred to the chopped lettuce was recovered by stomaching in DMEM and enumerated by plaque assay. MNV-1 transfer was lower from contaminated lettuce to cutting board (p<0.05) than that from a contaminated cutting board to lettuce. This same trend was observed between a stainless steel knife and lettuce. The MNV-1 transfer coefficient was lower when contaminated lettuce was chopped on a wood board (p<0.05) compared to a polyvinyl cutting board. Norovirus transfers readily between surfaces common in the preparation of fresh produce preparation, but the transfer coefficient appears to be dependent on the surface type. This research provides the scientific basis for the development of a risk assessment model for norovirus transfer during the fresh food preparation.
M.S. in Food Safety and Technology, December 2012
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Title: THE EVALUATION OF THERMAL INACTIVATION OF COXIELLA BURNETII NINE MILE PHASE II IN BOVINE AND NON-BOVINE MILKS BY MOST PROBABLE NUMBER-POLYMERASE CHAIN REACTION (MPN-PCR) ASSAY
Creator: Zhang, Cheng
Date: 2016, 2016-05
Description: As non-bovine milks become popular for human consumption, ensuring that standard bovine milk pasteurization conditions provide enough...
Show moreAs non-bovine milks become popular for human consumption, ensuring that standard bovine milk pasteurization conditions provide enough treatment for non-bovine milks is significant for food safety. Coxiella burnetii, an obligate intracellular bacterium, has been used as the reference microorganism for defining milk pasteurization conditions. To evaluate C. burnetii thermal inactivation in bovine and non-bovine milks at commercial pasteurization temperature, an MPN-PCR assay was developed to quantitate viable C. burnetii in milk. Using this assay, the thermal inactivation of C. burnetii and a potential nonpathogenic surrogate, Micrococcus luteus, was tested in bovine, buffalo, camel and goat milks. Milk in sealed glass vials was pre-heated in a water bath at 72°C and inoculated via a syringe with C. burnetii and M. luteus at a final concentration of ~6.5 log10 ge/mL (CFU/mL) each. The inoculated milk was heat-treated at 72°C for up to 16 sec, cooled in a crushed ice bath and serially diluted. Viable M. luteus was quantitated by plating on BHIA plates. For C. burnetii detection, 1 mL of each dilution was inoculated into 9 mL Acidified Citrate Cysteine Medium-2 (ACCM-2) in triplicate T-25 flasks to produce a 3- flask Most Probable Number (MPN) assay. Viability of C. burnetii was considered positive if an increase of ≥0.5 log10 ge/mL was detected by qPCR after 14 d growth in ACCM-2 media. The numbers of positive flasks at each dilution were used to calculate the remaining viable C. burnetii by MPN method. The average D-values for 72°C inactivation were 1.99 ± 0.21 sec, 0.79 ± 0.28 sec, 1.43 ± 0.30 sec, and 2.06 ± 0.71 sec for C. burnetii, and 5.47 ± 0.94 sec, 3.65 ± 0.45 sec, 3.48 ± 0.83 sec and 5.34 ± 1.54 sec for M. luteus in bovine, buffalo, camel and goat milks, respectively. For C. burnetii, D-values in camel and goat milks were not significantly different (p>0.05) from bovine milk, but the D-value in buffalo milk was significantly lower (p<0.05). These results indicate that non-bovine milks may not be a safety concern under standard milk pasteurization conditions, and M. luteus could be a good surrogate for C. burnetii thermal inactivation in milk.
M.S. in Food Safety and Technology, May 2016
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Title: EFFECTIVENESS OF CLEANING REGIMENS FOR REMOVING PEANUT, MILK AND EGG RESIDUE FROM PILOT-SCALE CEREAL BAR AND MUFFIN PROCESSING LINES
Creator: Zhang, Xi
Date: 2014, 2014-07
Description: Allergen cross-contact can be caused by inadequate cleaning of shared processing equipment. The objectives of this project were to evaluate...
Show moreAllergen cross-contact can be caused by inadequate cleaning of shared processing equipment. The objectives of this project were to evaluate the effectiveness of cleaning regimens on removing allergenic food residue from a pilot-scale cereal bar and muffin processing lines and measure the levels of allergens (peanut, milk and egg) transferred into allergen-free (control) cereal bars and muffins processed on an inadequately cleaned processing line. Another object was to investigate the analytical methods used (conventional ATP, sensitive ATP, total protein and lateral flow) to evaluate the effectiveness of allergen cleaning procedures. Cereal bars and muffins containing peanut flour, nonfat dry milk and egg powder (1000 or 5000 􀈝g/g for cereal bar and 100 or 5000 􀈝g/g for muffin) were manufactured on a pilot-scale processing line followed by one of four cleaning regimens: 1) push-through with control cereal bar dough or muffin batter, 2) scraping the equipment surfaces with rubber scrapers, 3) a rinse with hot (54-60°C) water until “visibly clean” and 4) a full cleaning cycle with alkaline detergent followed by use of a sanitizer. The adequacy of the cleaning treatments was assessed by swabbing locations (3 swabs/location) on the processing lines (cereal bar: mixer, depositor, conveyor belt; muffin: mixer, depositor, nozzle) followed by analysis of swabs with peanut-, milk-, and egg-specific lateral flow devices (LFDs). The cereal bar crosscontact study involved obtaining samples of the sheeted control dough transferred over the conveyor belt at 2 min intervals over a 30 min time span, or after approximately 100 kg of cereal bar dough was processed over the line previously contaminated with 5000 􀈝g/g allergen-incurred cereal bars. Similarly, allergen cross-contact from the contaminated muffin processing line into control muffins was measured by collecting xi 750g of control muffin batter until a total of 36 kg of batter were deposited. This was followed by allergen analysis of cereal bar and muffin samples (before and after baking) using quantitative ELISA kits. Results of LFD tests indicated that hot water rinse was effective for cereal bar processing line but not for the muffin line. Only the full cleaning cycle was effective at removing allergenic food residues for both processing lines. During the cross-contact study, substantial levels of peanut, milk and egg were detected in samples obtained both before and after baking. Cereal bar dough produced on the contaminated lines contained up to 71.9 ± 48.9 μg/g egg, 23.3 ± 1.3 μg/g milk, and 5.0 ± 0.4 μg/g peanut and as high as 2929.7 ± 98.8 μg/g egg, 1894.9 ± 87.7 μg/g milk, and 193.2 ± 20.6 μg/g peanut in muffin batter. Overall, these results illustrate the importance of validated cleaning protocols for preventing allergen cross-contact on shared processing lines.
M.S. in Food Safety and Technology, July 2014
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Title: GROWTH, INACTIVATION, AND SURVIVAL OF SALMONELLA ON SESAME SEEDS DURING TAHINI PROCESSING AND REFRIGERATED STORAGE OF TAHINI
Creator: Zhang, Yangjunna
Date: 2016, 2016-05
Description: Salmonella can survive for long period of time in low-moisture foods and cause human illness after consumption of contaminated foods. Recently...
Show moreSalmonella can survive for long period of time in low-moisture foods and cause human illness after consumption of contaminated foods. Recently, sesame seeds and tahini (sesame seeds pasta), have been identified as unusual sources of salmonellosis. Controlling specific steps during tahini processing and storage of tahini may minimize the risk of Salmonella contamination. This study examined the fate of Salmonella in different steps of tahini processing and refrigerated storage of tahini. A four serovar cocktail of Salmonella was used for inoculation of sesame seeds and tahini. Bacterial populations were determined by aerobic plate counts on both selective and non-selective media. Water activity of samples was determined during processing and storage. For the soaking step during tahini processing, unhulled dry sesame seeds with aw of 0.1 were inoculated with Salmonella, held 24 h, and then soaked in water at ambient temperature. Populations were monitored at 0, 18, 22 and 24 h. Salmonella decreased by 2 - 3-log CFU/g during drying and then increased by 5 log CFU/g after rehydration. Separately, inoculated de-hulled seeds with two different initial aw were roasted at three different temperatures (95, 110, and 130 ºC) for 90 min. Both the Salmonella populations and aw were determined at 10 min intervals during roasting. Finally, inoculated sesame seeds were processed into tahini. As a comparison, the same quantity of uninoculated roasted sesame seeds were processed into tahini, and then inoculated post-processing. Tahini was stored at 4 ºC for 17 weeks. Approximately 8 log CFU/g of Salmonella was detected initially in the sesame seeds prior to roasting with a 1-log CFU/g reduction after 20 min at 95 ºC when the aw of seeds decreased quickly. For different roasting temperatures, the aw declined much faster and stopped decreasing during roasting, while populations continue decreasing throughout the whole roasting. To investigate survival of Salmonella during refrigerated storage of tahini, approximately 9 log CFU/g of Salmonella was inoculated onto sesame seeds or into processed tahini without significant reduction throughout 17 weeks (p > 0.05). These results suggest that Salmonella contamination can be an issue at any step of tahini manufacture.
M.S. in Food Safety and Technology, May 2016
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Title: FACTORS AFFECTING THE SANITIZER EFFICACY IN PREVENTING SALMONELLA TRANSFER DURING POSTHARVESTWASHING OF CUT LETTUCE
Creator: Zang, Mingxia
Date: 2014, 2014-07
Description: This study investigated the spread of Salmonella during postharvest washing of contaminated lettuce and determined the factors that affect the...
Show moreThis study investigated the spread of Salmonella during postharvest washing of contaminated lettuce and determined the factors that affect the efficacy of chlorine in preventing Salmonella cross-contamination. A bench-scale washing system was assembled. It consisted of a 15 gal tank equipped with a submersible pump and various probes to measure wash water properties including pl-l, temperature, chlorine level. oxidation reduction potential (ORP), turbidity, and total organic carbon (TOC) level. Eight grams of cut romaine lettuce inoculated with approximately 7 log CFU/g of Salmonella typhimurium expressing green fluorescent protein were added to 40 L of sterile tap water or spent wash water collected from a commercial produce processing facility together with 800 g of uninoculated lettuce and washed for 2 min. Washing trials were performed at 3°C under different levels of chlorine treatment (0. 5, 10, 20 and 30 ppm of sodium hypochlorite). Small-scale (100 mL) experiments were performed to determine the effects of organic matter (lettuce homogenate) and solids (play sand) on the efficacy of chlorine in wash water. Without chlorine treatment, the spread of Salmonella occurred during lettuce washing in both sterile tap water and in spent industry water. With 5 ppm ofchlorine. although no Salmonella was detected in the wash water, the pathogen was found in the uninoculated lettuce after culture enrichments. When the chlorine level increased to either 10 or 20 ppm of chlorine, no Salmonella was detected in the wash water or the uninoculated lettuce. Similar experiments were performed using the spent industry water. Salmonella transfer occurred at chlorine of 10 or 20 ppm. Transfer was prevented when the chlorine level was raised to 30 ppm. IX Data from the small-scale experiments indicated that the increase in organic contents resulted in a lower level of free chlorine and a greater survival of Salmonella. At 5 ppm of chlorine, the level of Salmonella increased from not detectable « 1 log CFU/ml) to completely unaffected (4.3 ± 0.4 log CFU/ml) when the TOC level increased from 10.6 ± 10.4 to 164.0 ± 21.2 mg/L. Also, the increase in solid contents led to a greater survival of Salmonella even though the free chlorine level remained unchanged. At 0.5 ppm of chlorine, the level ofSalmonella increased from not detectable « 1 log CFU/ml) to completely unaffected (4.2 ± 0.1 log CFU/ml) when the turbidity level increased from 0.7 ± 0.5 to 378.2 ± 53.5 NTU. In summary, the use of sufficient chlorine could prevent Salmonella cross-contamination but the effective chlorine level was affected by the organic load and solid content present in the wash water. Since the chlorine efficacy was the key to preventing cross-contamination and organic load was an important factor affecting the chlorine efficacy, measurements of the organic load was needed to determine the level ofchlorination needed in the wash water. However, current methods for measuring TOC took a few hours to perform. Turbidity measurements which could be done in a minute had been frequently used in the produce industry to determ ine wash water quality. In this study. it was found that a linear correlation could be established between turbidity and TOC suggesting that turbidity could be a good predictor of the organic load in produce wash water.
M.S. in Food Safety and Technology, July 2014
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