Browsing by Author "Pierson, Merle D."
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- The Affects of Explosively and Electrically Generated Hydrodynamic Shock Waves on the Bacterial Flora of Beef and PoultryLorca, Tatiana Andrea (Virginia Tech, 2002-07-19)The affects of hydrodynamic shock wave treatment on the bacterial flora of raw beef and poultry were evaluated. Hydrodynamic shock waves were generated in an aqueous treatment medium by either the detonation of two types of explosive charges (explosively-generated hydrodynamic shock waves [EHSW]) (a binary or a molecular explosive) or by electrical discharge (high voltage arc discharge Hydrodyne (TM [HVADH; Hydrodyne, Inc.]). A variety of sample types (whole steaks, ground beef, a water and ground beef slurry) were used to determine the lethality affects of EHSW on cells of the marker microorganism Listeria innocua suspended in a simple broth medium. These sample types were used in order to evaluate the affects of the process not only on the surface, but throughout the bulk of the samples in order to determine whether EHSW could also be used as a non-thermal alternative to reduce the bacterial flora of non-intact or ground meats. The levels of psychrotrophic, lactic, and coliform populations on the surface of whole eye of round steaks submitted to EHSW processing did not differ (P> 0.05) from those of untreated whole eye of round steaks. Parameters expected to influence the nature, magnitude, and propagation of the hydrodynamic shock wave were also varied and evaluated in order to determine which individual parameter or combination of parameters affected the bactericidal potential of EHSW or HVADH processing. Treatment with EHSW failed (P > 0.05) to produce lethality effects on the psychrotrophic, lactic, and coliform populations of ground beef, regardless of the composition and mass of explosive used, the number of successive EHSW treatments used, the relative distance between the explosive charge and the top surface of the sample, or the temperature of the water used in the treatment chamber. EHSW processing did not change (P >0.05) the bacterial population of treated ground beef samples when compared to untreated controls during a five day refrigerated storage study. No lethality effects were observed (P >0.05) in ground beef samples treated by HVADH when samples were subjected to one, two, or three successive HVADH treatments. Minimal penetration of surface inoculated bacteria was observed for both beef steaks and boneless skinless chicken breasts subjected to EHSW and HVADH, respectively. In EHSW-treated beef eye of round steaks, marker bacteria were detected within the first 300 um of tissue below the inoculated surface, 50-100 um beyond the depth of untreated surface inoculated steaks. In HVADH-treated boneless skinless chicken breasts, marker bacteria were detected within the first 200 um below the inoculated surface, 50-100 um beyond the depth of untreated surface inoculated boneless skinless chicken breasts. This suggests that although no difference in the bacteriological populations was observed between EHSW treated, HVADH treated, and untreated control samples of whole steaks (and ground beef treated with both HVADH and EHSW), HVADH and EHSW treatments affect the movement of surface bacteria. United States Department of Agriculture (USDA) guidelines suggest intact beef steaks be cooked to achieve a cooked color appearance on the surface and raw poultry be cooked to an internal temperature of 77° C to inactivate the pathogens Escherichia coli O157:H7 and salmonellae which are of concern in beef and poultry, respectively. By following these guidelines during proper cooking, consumers achieve thermal inactivation of these pathogens. Since the movement of the marker bacterium observed in treated steaks and boneless skinless chicken breasts was minimal, proper cooking of the products would be expected to inactivate vegetative bacterial cells at this depth. Therefore, EHSW and HVADH treated whole beef steaks and boneless skinless chicken breasts would not be expected to pose a bacterial hazard if the products were properly cooked.
- Binding mechanism of K88ab pili produced by enterotoxigenic Escherichia coliChoi, Suk Ho (Virginia Polytechnic Institute and State University, 1987)Binding of K88ab pili by brush border membrane and mucus from pig small intestine was characterized by inhibition assay and Western blot. In Western blot, K88ab pili were bound by two major brush border membrane polypeptides with molecular weight of 61,500 and 57,000 in addition to numerous minor polypeptides and a major mucus polypeptide with molecular weight of 27,500. The results from Western blot assays with periodate oxidized and carbamylated brush border membrane and inhibition assay with brush border membrane glycopeptide suggest that amino groups (rather than carbohydrate) present on the protein moiety are a part of the recognition site for K88ab pili of receptor polypeptides in brush border membrane. Differences were obtained in the binding patterns of K88ab pili when brush border membranes were prepared from small intestines obtained from 2-, 21-, and 42-day-old piglets as well as adult hogs. Binding of K88ab pili by mucus polypeptides was greater when prepared from small intestines obtained from 2-day-old piglets than from piglets of other ages and adult hogs. In inhibition assay, most fractions from sow milk and colostrum inhibited binding of K88ab pili. After gel filtration of colostral whey, fractions which contained IgG, IgA, and IgM produced the strongest inhibition of K88ab binding. Among fractions prepared from cow milk, casein and skim milk significantly inhibited binding of K88ab pili. In Western blot, αs1-casein, immunoglobulin chains, and MFGM polypeptides in sow milk and colostrum were shown to be able to bind K88ab pili. Additionally, αs1-casein was the major protein in bovine milk responsible for binding K88ab pili. In dot blot assay, IgG as well as brush border membrane could strongly bind K88ab pili. However, bovine αs1-casein showed only weak binding of K88ab pili. Binding of K88ab pili to these proteins and brush border membrane was inhibited by carbamylation and by addition of 100 mM D-galactosamine. The results suggest that the K88ab-binding proteins in milk and colostrum compete to bind K88ab pili with the receptors in the brush border membrane and that mechanisms involved in binding of K88ab pili by these proteins is similar to that by brush border membrane.
- Biogenic Amine Analysis of Fresh and Stored Bluefish (Pomatomus Saltatrix) and Microbiological Survey of Histamine-Forming BacteGingerich, Todd Matthew (Virginia Tech, 1998-08-20)Changes in histamine, putrescine, and cadaverine concentrations in fresh and stored bluefish (Pomatomus saltatrix) were determined using a new HPLC method. The HPLC method utilized a 5.0% (w/v) trichloroacetic acid (TCA) extraction, pre-column fluorescamine derivitization, and fluorescence detection. The derivatives were stable over 24 h. The 5% TCA extraction produced percent recoveries of 98.6%, 98.7, and 100.0% for histamine, cadaverine, and putrescine respectively. The HPLC process including extraction, derivatization, and HPLC analyses was conducted in less than 45 minutes. Fresh bluefish was found to contain between <1 ppm and 99 ppm histamine, and no cadaverine or putrescine. Fresh bluefish fillets were stored at 5, 10, and 15 degrees C until sensory rejection. Fresh bluefish fillets inoculated with Morganella morganii were also stored at the same conditions. Histamine levels as high as 2200 ppm were observed in the inoculated fish stored at 15 degrees C. Overall, histamine achieved higher levels in the bluefish pieces inoculated with Morganella morganii. Histamine was present in greater amounts than putrescine and cadaverine in the bluefish samples. Histamine levels at each temperature exceeded the 50 ppm advisory level established by the FDA before 100% sensory rejection. Putrescine levels increased at each temperature during storage. Cadaverine was present only in uninoculated bluefish stored at 15 degrees C. Consumer risk from histamine poisoning seems to be the greatest in those fish stored at 5 degrees C where acceptance levels were higher and histamine levels above 100 ppm were observed. The presence of histamine-forming bacteria in fish-processing facilities was studied. Environmental sampling techniques were conducted in the Hampton Roads area of Virginia in fish-processing facilities that regularly handle scombroid fish or other fish which are known to accumulate histamine levels greater than 50 ppm. Surfaces that come into contact with the fish were swabbed and the histamine-forming bacteria from these areas were identified. One isolate each of Klebsiella ozaenae and Vibrio alginolyticus, and two isolates of Aeromonas sp. were found in the processing facilities. The study concluded that histamine-forming bacteria do not make up a large part of the microflora associated with fish-processing facilities. Fishing vessels were also sampled and no histamine-forming bacteria were identified.
- Decision making strategy in the selection of cook-chill production in hospital foodservicesGreen, Claudia G. (Virginia Tech, 1992-06-15)The primary purpose of this study was to develop and test a model for the process of making the decision to select/not select cook-chill for hospital food services. A second purpose was to determine the nature of the decision strategy, analytical versus intuitive, most predictive of satisfaction with cook-chill. A generic decision model was developed based on an extensive review of literature on decision making. Due to the lack of research on food service systems, a modified Delphi technique was used to identify 1) the factors critical in the process of making the decision to select/not select cook-chill and 2) the characteristics of a successful hospital cook-chill operation. The information gathered from the Delphi technique was used to develop a questionnaire which would measure the applicability of the generic model to the decision to select/not select cook -chill food production. The generic model was composed of five decision components and one satisfaction component. Using the model as a framework, a questionnaire was developed to test the relationships between the components of the model. Correlations between these components revealed that the use of the model was significantly related with satisfaction with the decision to select/not select cook-chill. A "Checklist for the Process of Making the Decision to SelectINot Select Cookchill Food Production for Hospital Foodservices" was developed using the model and questionnaire as frameworks. The Checklist consists of 136 questions: 101 questions measuring the decision process and 35 questions measuring satisfaction with the decision. For the purposes of this study, analytical decision making was defined as a process where objective, as opposed to subjective information, was available and was used in the process of making the decision. The Checklist consisted of questions to which there was a "yes" or "no" response. The higher the number of "yes" responses on the decision component questions, the more analytical the decision process and the higher the correlation with satisfaction. It was statistically determined that 37 "yes" responses resulted in satisfaction with the decision process. The lower the number of "yes" responses on the decision component questions, the more intuitive the decision process and the lower the correlation with satisfaction. The results of this study are significant in that an extensive review of literature between 1950 and 1990 showed that there was little empirically based research on foodservice systems. The existing research prior to this study did not provide enough information to develop a model for the process of making the decision to select/not select cook-chill production for any foodservice operation. The model developed and tested in this research is generic in nature and should apply equally well in a variety of types of foodservices. It may be necessary to make minor adaptations to the Checklist to address the unique nature of various types of foodservices such as schools, college/universities, military, prisons, hotels, and restaurants.
- Development of a New Class of Viral Disinfectants: Enzymatic Inactivation of Sa-11 RotavirusWalker, Shawn Christopher (Virginia Tech, 1997-12-09)The non-enveloped, pH- and heat resistant rotavirus (RV), which is cross species-infective among cattle, swine and humans may cause dehydration and high mortality in the young. Rotaviruses are inactivated only by corrosive and toxic disinfectants. In this study, the effects of bacterial proteases as a new type of disinfectants on simian rotavirus (SA-11) were analyzed. SA-11 rotavirus replicates in cells causing cytopathic effect (CPE) and is similar in protein composition to cattle and swine RV. Preliminary experiments tested the temperature and pH sensitivity of SA-11 rotavirus. At pH 8.5, 45°C was the highest temperature at which no loss in viral titer was seen, and the virus was still infective following treatment at 65°C for 2 hrs. pH sensitivity tests were then conducted for two hours at 45°C, with pH 5 being the lowest and pH 8.5 being the highest at which no loss in titer was observed. Four proteases were then tested for effectiveness at inactivating SA-11 rotavirus at their pH optimal at 45°C. Alcalase was selected as the most efficient protease. Alcalase was found to inactivate SA-11 at 25°C, and pH 8.5 in 3 days, indicating that enzymes were relatively effective at lower temperatures. SA-11 rotavirus virus was then tested for sensitivity to pH at 25°C and 15°C in absence of enzyme. At pH 2, 25°C a ~4 log reduction was seen following 15 min of treatment, with viable virus still remaining after 8 hrs, at 15°C a ~1.75 log reduction was seen following 2 hrs, and a ~4 log reduction following 8 hrs of treatment. At pH 4 and 6, at 25°C and 15°C no effect on SA-11 titer was seen after 120 hrs treatment. The enzyme was then tested at 1.0% and 0.1% enzyme concentration, at 15°C and 25°C, and pH 6 to determine efficacy of enzyme at sub-optimal conditions. Following treatment with 1.0% Alcalase at 25°C a ~3.25 log reduction, and at 15°C, 1.0% Alcalase, a ~1.75 log reduction was seen at 120 hrs. At 15°C, 1.0% Alcalase a ~1.75 log reduction was seen at 120 hrs. Treatment with 0.1% Alcalase at 25°C, pH 6 resulted in ~2.25 log reduction after 120 hrs. At 15°C, 0.1% Alcalase a ~1.25 log reduction was seen following 120 hrs. The results showed that proteases, used as viral disinfectants, were not as effective at inactivating rotaviruses under simulated field conditions as originally hoped, nevertheless the ease of application and moderate but definite efficacy against rotaviruses may help reduce rotaviral infections and severity of clinical signs in young animals.
- Effect of environmental stress on the ability of Listeria monocytogenes Scott A to attach to food contact surfacesSmoot, L. Michele (Virginia Tech, 1996)The attachment and detachment of Listeria monocytogenes Scott A to Buna-N rubber and stainless steel under varying conditions of temperature and pH were investigated. Numbers of attached cells increased with increasing attachment temperatures (10° to 45°C) and time (up to 120 min) for both Buna-N rubber and stainless steel. Cells attached at higher levels on stainless steel at all temperature and pH levels investigated. Rate of attachment was found to be significantly lower at 10°C than 30° and 45°C on Buna-N rubber. When L. monocytogenes was grown at 10°, 30°, and 42°C before exposure to Buna-N rubber at 30°C, differences in rates of adhesion were not significant. A downward shift in the cell suspension holding temperature immediately prior to attachment to Buna-N rubber at 10°C resulted in reduced adhered cell populations. A similar upward shift did not affect attachment at 45°C. Altering the pH of the attachment environment within the pH range of 4 to 9 did not affect the maximum levels of attached cells to Buna-N rubber. However, the measured rates of adhesion indicated slower attachment occurs under alkaline conditions. Growth pH was also found to significantly affect rates of attachment and maximum adhered cell populations to Buna-N rubber. Compared to Buna-N rubber, the rate of attachment to stainless steel was markedly more rapid for all temperature and pH conditions studied and could not be calculated. The ease of removal for cells adhered to Buna-N rubber was significantly affected by growth temperature, but not growth pH. Significant differences in detachment were also found between Buna-N rubber and stainless steel, inferring a stronger attachment to Buna-N rubber. Cell surface hydrophobicity was affected by both growth temperature and growth pH, but differences in hydrophobicity could not be correlated to differences in rates of attachment. Addition of 0.01% trypsin to the attachment medium during cell suspension exposure to both test surfaces resulted in a 99.9% reduction in the adhered cell population when compared to controls. This suggests that proteins may play a role in the initial attachment process for L. monocytogenes.
- The effect of heat shock, growth atmosphere, and recovery atmosphere on the survival of Escherichia coli 0157:H7 to heatMurano, Elsa Alina (Virginia Tech, 1990)E. coli 0157:H7 is an important foodborne pathogen, responsible for several outbreaks of hemorrhagic colitis where improperly cooked hamburger meat was thought to be the vehicle. Various time/temperature combinations were used to determine the optimum conditions of heat shock which would result in the greatest number of survivors to a 55°C heat treatment. The optimum conditions were 42°C for 5 minutes and were used throughout the study. Heat shock of aerobically grown cells resulted in an increase in the mean D value after a 55°C heat treatment by a factor of 2.1 over nonheat-shocked controls. Heat shock of anaerobically grown cells also resulted ina significant increase in mean D value over nonheat-shocked controls. Anaerobic growth itself resulted in an increase in the ability of the cells to survive the 55°C heat treatment when compared with aerobically grown cells. Both heat-shocked and anaerobically grown cells contained a protein corresponding to a sigma³² subunit of RNA polymerase which has been identified as the 71,000 Galton heat shock protein characteristic of E. coli cells. Anaerobic plating resulted in a significant increase in the mean D values of both aerobically grown and anaerobically grown cells. The largest increase in mean D values was observed in aerobically grown non-heat-shocked cells, which increased by a factor of 2.3 when plated anaerobically instead of aerobically. The activities of catalase and superoxide dismutase in aerobically grown and anaerobically grown cells were studied to determine the reason why anaerobic plating enhanced recovery of cells. The activities of both enzymes were eliminated after heat treatment at 55°C for 20 minutes, regardless of whether the cells were heat-shocked or not. The ability of heat shock and anaerobic growth to protect the cells from a subsequent heat treatment was tested by measuring the rate of release of cell materials during heating at 55°C. Heat-shocking and anaerobic growth resulted in even faster release of cell materials during heating than controls, suggesting that neither of these stresses protected the cells against the effects of heat. The effect of heat shock on cell injury was studied. Heat shock of aerobically grown cells resulted in the greatest difference in log number of cells between cells plated in nonselective medium vs. selective medium. Thus, more cells were injured if heat-shocked than if not heat-shocked. Heat-shocking of anaerobically grown cells also resulted in more injured cells than non-heat-shocked controls.
- Effect of hydrogen peroxide and other protease inhibitors on Cryptosporidium parvum excystation and in vitro developmentKniel, Kalmia E.; Sumner, Susan S.; Pierson, Merle D.; Zajac, Anne M.; Hackney, Cameron Raj; Fayer, Ronald; Lindsay, David S. (American Society of Parasitology, 2004-08)This study was undertaken to observe the effects of hydrogen peroxide on Cryptosporidium parvum oocysts with respect to protease activity in comparison to known protease inhibitors. In assessing the possible mechanisms of action of hydrogen peroxide, treatment effectiveness was analyzed using 3 assays and the potential roles of proteases and cations were considered. Treatment of C. parvum oocysts with hydrogen peroxide inhibited protease activity up to 50% compared with untreated controls. Treatment of oocysts with chemicals that affect sulfhydryls, including N-ethylmaleimide and dithiolthreitol, inhibited protease activity by > 90%. Treatment of oocysts with these chemicals, along with the protease inhibitors, phenylmethylsulfonyl fluoride (PMSF), ethylenediamine-tetraacetic acid, and cystatin, inhibited protease activity as well as in vitro excystation and infection in a cell culture assay. Several mechanisms may result in the successful inhibition of infection and excystation by hydrogen peroxide treatment, including: oxidation of oocyst wall proteins or lipids, chelating of cations necessary for infection, or hydroxyl radical-induced DNA damage to sporozoites, or both.
- Effect of modified atmosphere packaging on growth of Listeria monocytogenes and nonproteolytic Clostridium botulinum in cooked turkeyLawlor, Kathleen A. (Virginia Tech, 1999-01-12)The growth of Listeria monocytogenes and nonproteolytic Clostridium botulinum type B spores in cooked, uncured turkey was investigated separately under varying conditions of modified atmosphere packaging (MAP), refrigerated and temperature-abuse storage, and lactic acid bacteria (LAB) competition. L. monocytogenes (LM) growth was suppressed when initially outnumbered 3.5 logs:1 or 2.1 logs:1 by naturally-occurring LAB, but not when the initial LAB:LM population ratio was equivalent. Lowering storage temperature from 10 degrees to 4 degrees C enhanced the inhibitory effect of CO₂ in the packaging atmosphere, and extended the period of product olfactory acceptability. When the LAB:LM population ratio was equivalent, objectionable odors were not detected in most of the samples, despite LAB counts in excess of 10E⁸/g. This raises concerns with respect to public health, since high levels of L. monocytogenes can be present in MAP meat and poultry products without accompanying signs of overt spoilage. Cellular fatty acid (CFA) analysis was a valuable tool for distinguishing between phenotypically distinct isolates of LM inoculated into MAP turkey. Fatty acid composition of foodborne outbreak-associated (serotype 4) and non-outbreak-associated (serotype 1) strains of LM correlated with antigenic type (4 or 1) and agglutination reaction (granular or flocculent). Strain ATCC 43256 (serotype 4b) produced a consistently unique CFA profile, making it the easiest of the four test strains to be differentiated. Analysis of additional LM serotypes, as well as examination of existing clinical and environmental CFA databases for correlations between fatty acid profiles and diagnostic characteristics of LM, is necessary before CFA analysis can be effectively applied as an epidemiological tool for tracking the distribution of LM strains in food products and throughout the farm-to-table food chain. Reduced storage temperature significantly delayed botulinal toxin production and extended the period of olfactory acceptability of cooked turkey, but even strict refrigeration did not prevent growth and toxigenesis by nonproteolytic C. botulinum type B. Toxin was detected on day 7 for product stored at 15 degrees C and on day 14 for product stored at 10 degrees C, irrespective of packaging atmosphere. At 4 degrees C, toxin was detected on day 14 for product packaged without carbon dioxide, and on day 28 for product packaged with 30% carbon dioxide. At all three storage temperatures, toxin detection preceded or coincided with olfactory unacceptability, demonstrating the potential for consumption of toxic product when spoilage-signalling sensory cues are absent.
- The Effect of Sorbic Acid on the Survival oOf Escherichia coli 0157:H7, Salmonella, Listeria monocytogenes, and Staphylococcus aureus on Shredded Cheddar and Mozzarella CheeseRoberts, Alison K'Ann (Virginia Tech, 2002-12-15)The objective of this study was to determine the effectiveness of sorbic acid in inhibiting Escherichia coli 0157:H7, Salmonella spp., Listeria monocytogenes, and Staphylococcus aureus on shredded cheddar and mozzarella cheese over 70 days storage. Samples of cheese were inoculated and placed into bags with a sorbic acid (0, 0.1, 0.15, 0.2 and 0.3 %) and anti caking agent mixture and stored at 10 °C. Each variable was enumerated after 0,14,28,42,56, and 70 days of storage. Survival of E. coli 0157:H7 showed no significant difference from control in either cheese. There were significantly lower Salmonella counts for days 14 to 42 on mozzarella cheese. No significant differences in survival were found for cheddar cheese. There were significantly lower counts noted in L. monocytogenes, and S. aureus in mozzarella. Though no significant differences were found over time in the cheddar, most of the sorbate concentrations exhibited lower counts than control on days 14 and 28. Overall, in the presence of sorbic acid there was a more rapid decline in numbers of each test organism, especially against L. monocytogenes, and S. aureus for both high and low moisture cheeses.
- Effect of storage temperatures on the microbiological quality, safety, and viability of quahog clams, Mercenaria mercenariaBrenton, Carolyn E. (Virginia Tech, 1996-09-05)The objective of this project was to examine the effects of various storage temperatures and times on the microbiological quality, safety, and viability of hard shelled quahog clams. Samples were stored at four different incubation temperatures (3.3, 7.2, 10.0, and 12.S0C) for a period of three weeks, following their harvest from growing waters during the summer when the water temperatures were ~ SO°F, and during the winter when water temperatures were ~ 40°F. With regards to safety, clams were analyzed for two naturally-occurring pathogens, Vihrio parahaemolyticus and Vihrio vulnificus. Aerobic plate counts (APCs), coliforms, and fecal coliforms were determined to define the level of quality. During the summer, mesophilic APCs containing 2% NaCI ranged from 104 to 108 CFU/g, and during the winter, mesophilic APCs with salt ranged from < 100 ESPC to 104 CFU/g. Comparatively, during the summer, mesophilic APCs containing no added NaCI ranged from < 100 ESPC to 105 CFU/g, and during the winter, APCs without salt ranged from < 100 ESPC to 102 CFU/g. Coliform and fecal coliform counts ranged from < 0.3 to 61.1 MPN/g and < 0.3 to 24.4 MPN/g, respectively. During the summer, V. parahaemolyticus was isolated from 56% of the samples, with the highest concentration, 24,000 MPN/g, occurring on day 12 at 12.8°C.
- Effect of transport methods on recovery of bacteria from ground beef samplesGuilfoyle, John Rohan (Virginia Tech, 1977-06-05)A comparison of 2 basic methods presently used to transport perishable food samples intended for microbiological analysis is presented. A transport system using an appropriate, pre-chilled container with dry ice as the temperature contro11ant resulted in a significant1y higher (P ~ 0.01) survival rate of Clostridium perfringens vegetative cells in ground beef samples as compared to survivals in samples shipped in Trans Temp containers using canisters of a commercia11y formulated eutectic salts mixture as temperature contro1lant. Dry ice kept samples also resulted in greater recoveries of Staphylococcus aureus and the aerobic microf1ora~ Slightly higher recoveries of co1iforms and Escherichia coli were obtained from samples held by the Trans Temp procedure! Mixing samples 1:1 with 10, 20 or 30% (wt/vo1) buffered solutions of either dimethylsulfoxide or glycerol prior to freezing generally improved the survival of all microorganisms assayed regardless of the transport system tested. The results indicate that packaging perishable food samples with a volume of cryoprotective solute may be a useful adjunct to frozen transport systems thereby improving survival and allowing more complete recovery of selective micro-rganisms with existing assay procedures.
- Effects of Apple Development and Damage on the Internalization of Escherichia coli O157:H7 as Observed Under Field and Laboratory ConditionsHereford, Megan Lee (Virginia Tech, 2003-09-12)The number of food borne illnesses associated with the consumption of fresh fruits and vegetables and their minimally processed products (juices) has increased over the past years. Of particular interest is the ability of microbial pathogens to internalize and survive in fresh produce that are commonly used for juices. This research project addresses the issue of the ability of Escherichia coli O157:H7 to internalize and survive in whole apples before and after harvest. Four cultivars of apples, Redfree, Red Delicious, Golden Delicious, and York, were inoculated under field conditions with a surrogate strain of E. coli, Escherichia coli ATCC 25922. The Redfree cultivar was inoculated at the beginning of its growth stage (day 0), and again 30 days later, and sampled for two weeks, until E. coli was not recoverable through microbiological methods after three successive sampling days. Red Delicious, Golden Delicious, and York cultivars were spray inoculated with the surrogate strain two weeks before their anticipated harvest date and sampled every other day until E. coli was not recoverable for three successive sampling days. For each cultivar, the presence of E. coli ATCC 25922 was not detectable after 7 to 9 days. In the laboratory study the Red Delicious, Golden Delicious, Rome, and York cultivars received one of three treatments; unblemished control, bruising, or puncturing. The apples were inoculated by immersion in cold water containing E. coli O157:H7 GFP, incubated for three days then microbiologically analyzed for presence of the bacteria. In all cases, the punctured apples of each cultivar showed the greatest uptake of E. coli O157:H7 GFP. Escherichia coli O157:H7 GFP was visualized in flesh and core sections of untreated, bruised, and punctured apples of all cultivars. The microbe was found in between cells, but not within cells of the apple. Internalization of Escherichia coli in whole apples on the tree is not likely, and leads to the conclusion that internalization is a post-harvest problem. Internalization may occur before pressing or processing of apples, leading to an increased risk of infection with E. coli for consumers of apple products that are not properly treated to destroy pathogens. Internalization does occur when apples are immersed in solutions containing the pathogen Escherichia coli O157:H7, and better post harvest controls need to be implemented in order to prevent this in whole apples that are used for cider and juice production.
- Effects of modified atmosphere packaging on toxin production by Clostridium botulinum in raw aquacultured summer flounder fillets (Paralichthys dentatus)Arritt, Fletcher M.; Eifert, Joseph D.; Jahncke, Michael L.; Pierson, Merle D.; Williams, Robert C. (Int Assoc Food Protection, 2007-05-01)Packaging fishery products under vacuum atmosphere packaging (VAC) and modified atmosphere packaging (MAP) conditions can significantly extend the shelf life of raw, refrigerated fish products. There is considerable commercial interest in marketing VAC and MAP refrigerated (never frozen) raw fish fillets. The objective of this study was to determine if Clostridium botulinum toxin development precedes microbiological spoilage in raw, refrigerated flounder fillets. Aquacultured flounder (Paralichthys dentatus) individual fish fillets either were packed with a film having an oxygen transmission rate (OTR) of 3,000 cm3 m-2 24 h-1 at 22.8°C or were vacuum packaged or packaged under 100% CO2 with a film having an OTR of 7.8 cm3 m-2 24 h-1 at 21.1°C and were stored at 4 and 10°C. Samples were analyzed by aerobic plate count (APC) for spoilage and qualitatively for botulinum toxin with a mouse bioassay. The results demonstrate that flounder fillets (4°C) packaged with a film having an OTR of 3,000 were microbiologically spoiled (APC, >107 CFU/g) on day 15, but there was no toxin formation, even after 35 days of storage. However, at 10°C, toxin production occurred (day 8), but it was after microbial spoilage and absolute sensory rejection (day 5). Vacuum-packaged fillets and 100% CO2 fillets (4°C) packaged with a film having an OTR of 7.8 were toxic on days 20 and 25, respectively, with microbial spoilage (APC, >107 CFU/g) not occurring during the tested storage period (i.e., >35 days). At 10°C, in vacuum-packaged flounder, toxin formation coincided with microbiological spoilage (days 8 to 9). In the 100% CO2-packaged fillets, toxin formation occurred on day 9, with microbial spoilage occurring on day 15. This study indicates that films with an OTR of 3,000 can be used for refrigerated fish fillets and still maintain the safety of the product.
- Effects of UV Irradiation on the Reduction of Bacterial Pathogens and Chemical Indicators of MilkMatak, Kristen E. (Virginia Tech, 2004-11-22)Consumer demand for fresher and minimally processed foods has brought about a movement to find effective, non-thermal processing technologies for the treatment of milk. The influence of temperature on bacterial reduction in UV irradiated milk was tested. Commercially processed skim, reduced fat (2%), and whole milk samples were inoculated with a naladixic acid resistant E. coli O157:H7 surrogate (ATCC 25922), maintained at or brought to 4oC and 20oC, respectively, and then exposed to a UV light dose between 5.3-6.3 mJ/cm2 for approximately 1.5 sec using the CiderSure 3500 apparatus (FPE Inc., Macedon, NY). Bacterial concentrations before and after UV exposure were enumerated and the results indicated that processing temperature was not significantly related to bacterial reduction (p > 0.05). The results did indicate that skim milk samples had a greater bacterial reduction, regardless of processing temperature compared to reduced fat milk and whole milk samples (p < 0.05). Solids such as milk fat, protein, lactose and minerals, in the milk have a greater effect over bacterial reductions than processing temperatures. Traditional goat cheeses are produced using unpasteurized milk, which increases the food safety concerns for these types of products. Fresh goat's milk was inoculated to 107 cfu/ml with Listeria monocytogenes (L-2289) and exposed to UV light using the CiderSure 3500 apparatus. Inoculated milk was exposed to an ultraviolet dose range between 0 and 20 mJ/cm2 to determine the optimal UV dose. A greater than 5-log reduction was achieved (p < 0.0001) when the milk was processed 12 times for a cumulative exposure time of roughly 18 sec and a cumulative UV dose of 15.8 +/- 1.6 mJ/cm2. The results of this study indicate that UV irradiation could be used for the reduction of L. monocytogenes in goat's milk. Organoleptic consequences of goat's milk treated with UV technology were assessed. Olfactory studies were conducted and a highly significant difference was determined between the odor of fresh goat's milk and UV processed milk (p < 0.05). The extent of lipid oxidation and hydrolytic rancidity was measured by thiobarbituric acid reactive substances (TBARS) and acid degree values (ADVs). Results indicated that as the UV dose increased, there was a significant increase in TBARS values and ADVs of the milk samples (p < 0.05). Milk samples were processed using the UV processor under the same conditions as previously described without exposure to the UV source to determine if the agitation from pumping was causing off-flavors by way of hydrolytic rancidity. The ADVs from these samples increased at the same rate as the UV irradiated samples; however, sensory studies indicated that the increase of free fatty acids (FFA) was not enough to cause detectable off-odors in the milk. Solid phase microextraction and gas chromatography (SPME-GC) was utilized to quantify the production of volatile compounds that were formed due to UV processing. The formation of pentanal, hexanal and heptanal was identified after as little as 1.3 mJ/cm2 UV dose. Peak areas were measured and analyzed after 7.8 mJ/cm2 and 15.6 mJ/cm2 and were determined to increase significantly as UV dose increased (p < 0.05). The chemical analyses supported the findings from the olfactory studies. The outcome of this research showed that UV irradiation at the wavelength 254 nm, was detrimental to certain chemical properties of fluid milk. The properties that were perceived as negative in fluid milk may be considered an attribute in certain types of cheese and future studies in the cheese production sector should be considered. Other applications for this technology could be for use in developing countries where milk is not typically processed because of the high costs of thermal pasteurization. On-farm applications for the treatment of replacement milk should also be considered.
- Efficacy of Detergent Rinse Agents to Remove Salmonella and Shigella spp. from the Surface of Fresh ProduceRaiden, Renee Mary (Virginia Tech, 2002-08-16)Fresh produce has been implicated in several foodborne outbreaks. A primary site of microbial contamination for produce occurs on the surface during production and handling. An approach to reduce contamination is to sample the surface of produce. This study used different detergent agents at 22°C and 40°C to determine their efficacy for recovery of pathogenic bacteria, from surfaces of several produce types and examined survival of organisms in detergents over time. Strawberries, tomatoes and green leaf lettuce were dip inoculated in a 6-6.5 LOG CFU/ml cocktail of nalidixic acid resistant organisms. After drying, produce were rinsed with either 0.1 % sodium lauryl sulfate (SLS), 0.1% Tween 80, or water at different temperatures. Rinse solutions were plated onto Tryptic Soy agar supplemented with 50-ppm nalidixic acid (TSAN). About 4 LOG CFU/ml of Salmonella, and 3-LOG CFU/ml Shigella were recovered, with slightly lower recovery from tomatoes. Inoculated strawberries rinsed with SLS, displayed minimal recovery at ~1.5-LOG CFU/ml at 22°C, and <1-LOG CFU/ml at 40°C. When whole strawberries treated with SLS were analyzed, few Salmonella were recovered. Lack of recovery of Salmonella rinsed with SLS, suggests SLS may be inactivating Salmonella, especially at elevated temperatures. Detergent solutions were inoculated with 3-LOG CFU/ml cocktail and incubated for up to 32 hours at 22°C, and 40°C. Aliquots were plated onto TSAN at varying times. All solutions at 40°C allowed Shigella to grow. SLS gave initial drops in Salmonella populations followed by slight recovery. SLS may cause an initial injury of Salmonella. While organisms were able to survive in detergents, the application of detergents to produce was no more effective in recovery of organisms from produce than water.
- Efficacy of Selected Chemicals on the Attachment and Survival of Campylobacter jejuni on Chicken Breast SkinArritt, Fletcher Marion (Virginia Tech, 2000-12-06)Campylobacter is considered to be the leading cause of acute bacterial gastroenteritis in humans in the United States with Campylobacter jejuni being responsible for 80-90% of those infections. Many cases of Campylobacter gastroenteritis have been linked to the consumption of raw or undercooked chicken. The population of bacteria on the breast skin has been reported to be greater than on other edible portions of the chicken carcass making this an important site to control the organism and to study bacterial attachment properties. This research examined the efficacy of trisodium phosphate (TSP)(10%), cetylpyridinium chloride (CPC)(0.1% & 0.5%), acidified sodium chlorite (ASC)(0.1%), Tween 80 (polysorbate 80) (1%) and water (50°C) for reducing the number of viable Campylobacter jejuni on inoculated chicken breast skin. All chemicals were evaluated using contact times of 30 sec., 3 min. or 10 min. Statistically significant (p £ 0.05) differences in the reduction of C. jejuni populations were observed across chemical treatments and contact time. When bacteria were applied before treatment, a reduction of >1.0 log10 CFU/skin was achieved with 0.5% CPC (2.89), 10% TSP (1.63), 0.1% ASC (1.52), and 0.1% CPC (1.42). When bacteria were applied after treatment, a reduction of >1.0 log10 CFU/skin was achieved with 0.5% CPC (4.67) and 10% TSP (1.28). The main effects of contact time were statistically significant (p=0.02) only when bacteria were applied after treatment.
- Enhanced recovery of injured and noninjured cells of Bifidobacterium species from water and dairy productsArany, Catherine Beatrice (Virginia Tech, 1992-09-03)Bifidobacterium spp. are anaerobic, Gram-positive, nonmotile bacteria that are a major component of intestinal microbiota. They are potential indicators of human fecal pollution in shellfish harvesting waters. In addition, Bifidobacterium spp. are used as supplements in dairy products. These bacteria are easily injured and it is important to have methods that will recover all cells (injured and uninjured) present in water and food samples. The objectives of this research were to develop a repair detection (RD) procedure to be used with VPI's anaerobic roll tube apparatus for improving the recovery of Bifidobacterium and to compare this method with existing enumeration methods. Bifidobacterium adolescentis cells were injured by exposure to pond water. Cells were enumerated using a modification of Human Bifid Sorbitol Agar (MHBSA). MHBSA was modified by substituting phenyl red for bromocresol purple and adding methylene blue as an indicator of oxidation/reduction.
- Evaluation of chemical treatments and ozone on the viability of Cryptosporidium parvum oocysts in fruit juicesKniel, Kalmia E. (Virginia Tech, 2002-03-28)Cryptosporidium parvum is a protozoan parasite historically associated with waterborne and more recently foodborne outbreaks of diarrheal illness. Contamination of certain foods, such as unpasteurized apple cider, with infective oocysts may occur as oocysts are shed in the feces of common ruminants like cattle and deer that graze in and around orchards. Cryptosporidiosis can result in a severe illness for previously healthy individuals and a life-threatening illness in immunocompromised individuals. Disease occurs after the ingestion of small infective oocysts (4 to 5 mm in size). The relatively thick membrane of the oocysts allows them to be resistant to chlorine and many other environmental pressures, making oocysts difficult to inactivate. In this study, alternative treatments to pasteurization were evaluated for their ability to inhibit C. parvum oocyst viability in fruit juices. Oocyst viability was analyzed with a cell culture infectivity assay, using a human illeocecal cell line (HCT-8) that is most similar to human infection. The percent inhibition of infection by each treatment was determined along with the corresponding log reduction for the treatments found to be most effective. Infection by treated oocysts was compared to that of control untreated oocysts. Cell monolayers were infected with 10⁶ treated oocysts or a series of 10-fold dilutions. Parasitic life stages were visualized using an immunohistochemistry system and 100 microscope fields counted per monolayer. Organic acids and H₂O₂ were added on a wt/vol basis to apple cider, orange juice, and grape juices. Malic, citric, and tartaric acids at concentrations from 1%-5% inhibited C. parvum infectivity of HCT-8 cells by up to 88%. Concentrations ranging from 0.025%-3% H₂O₂ were evaluated where addition of 0.025% H₂O₂ to each juice resulted in a >5 log reduction of C. parvum infectivity as determined with an MPN-based cell culture infectivity assay. Treating apple cider, orange juice, and grape juice with ozone for a time period of 30 seconds up to 15 minutes at 6° and 22°C (0.9 g/L flow rate) inhibited C. parvum viability to > 90% as monitored in the cell culture assay. It is hypothesized that oocyst wall proteins that are necessary for infection are oxidized by the reactive oxygen species generated from the decomposition of the ozone and hydrogen peroxide treatments. These treatments or combinations thereof may offer potential alternatives to traditional pasteurization for fruit juices to successfully inhibit C. parvum viability.
- An Evaluation of the Role of Temperature on the Safety and Quality of Raw Shellstock Oysters and BluefishLorca, Tatiana A. (Virginia Tech, 2000-11-07)Raw oyster shellstock was subjected to abuse conditions (7, 13, and 21°C) and sampled over a ten day storage period to gather scientific data to aid in determining whether spoilage occurred in the raw product over time before proliferation of pathogenic flora (Vibrio vulnificus) made the product unsafe. Spoilage was evaluated through pH measurements of a homogenate of the shucked meat and liquor. The olfactory acceptability of the raw oysters was evaluated in concert with the microbial and chemical evaluations. At all storage conditions, halophilic bacteria outgrew V. vulnificus by a minimum of 1 log CFU/g oyster (Colony Forming Units per gram) (p < 0.05). Olfactory acceptability was below 40% when V. vulnificus growth was at its highest (p < 0.05). Refrigerated storage should be considered a CCP for raw shellstock since even moderate temperature control kept V. vulnificus below 104 approximately 1-2 Logs below the estimated infective dose for the majority of the population.
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