VTechWorks Repository :: Browsing by Author "Hackney, Cameron Raj"

Browsing by Author "Hackney, Cameron Raj"

Now showing 1 - 20 of 37

Acceptability and Shelf-Life of Fresh and Pasteurized Crab Meat Stored Under Different Environmental Conditions
Tyler, Carla Gutierrez (Virginia Tech, 2009-02-02)
Crab meat is important to the economy of coastal Virginia. The objectives of this study were to complete a shelf-life study on two different packaging styles of fresh crab meat and to test the inhibition capabilities of Carnobacterium piscicola against the pathogen, Listeria monocytogenes. In a shelf-life study, a 12 ounce food grade polyethylene traditional snap-lid container of fresh crab meat was compared to an 8 ounce SimpleStep® trays with Cryovac™ film of equally fresh crab meat sealed with 10,000 cc/m2/24hr oxygen transmission rate (OTR) film. Eleven g samples were used for the microbial shelf-life study conducted at 4°C for 12 days. Aerobic plate counts of crab meat indicated microbial growth from the SimpleStep® trays with Cryovac™ film in 10,000 cc/m2/24hr OTR versus the polyethylene snap-lid was not significant (P>0.05). In objective two, 25 g samples of fresh and pasteurized blue crab (Callinectes sapidus) meat were inoculated with 0.1ml of each, C. piscicola and L. monocytogenes. Three different concentrations of the inoculation levels were studied on select days at both 4°C and 10°C. Microbial spoilage was defined as 107 CFU/g. In fresh crab meat, at both 4°C and 10°C, crab meat spoilage occurred at 7 days or less. In the pasteurized crab meat, at 4°C and 10°C, spoilage did not occur prior to 26 days, and studies were terminated at 28 days of storage. The growth of the two organisms in fresh crab meat was found to be significant for the differing concentration levels and sampling days (P<0.05). The growth of the two organisms in pasteurized crab meat was significant for different concentration levels, sampling days and temperature (P<0.05). In both fresh and pasteurized crab meat, regardless of the inoculation ratios, the L. monocytogenes and C.piscicola followed similar growth trends, but L. monocytogenes was higher in the 2:2 CFU/g concentration and lower at the 6:2 CFU/g concentration level. Although C. piscicola did not completely inhibit L. monocytogenes growth at any concentration ratio, some inhibition was observed.
Aerosol exposure biotesting for package integrity testing
Keller, Scott W. (Virginia Tech, 1995-01-05)
The objective of this study was to determine how hole diameter, channel length, test organism motility, concentration and aerosol exposure time affected microbiological contamination of sealed flexible pouches. Nickel microtubes with 10 μm and 20μm hole diameters and lengths of 5 mm and 10 mm were used in various combinations to create seal defects in 128 retortable pouches. A 119,911 cm³, exposure chamber was used to distribute an aerosol with a particle size of 2.68 μm, infected with motile and isogenically mutated nonmotile Pseudomonas fragi TM 849 in concentrations of 10² or 10⁶ cells/mL. Fifteen and 30 minute aerosol exposure times were used. Six pouches tested positive for test organism growth after a 72 hour incubation period. Pouch contamination via microbial ingress was significant (P < .05) for test organism motility (motile) and concentration (10⁶ cells/mL).
Capture filtration for concentration and detection of selected microorganisms in milk
Byrne, Robert Duane (Virginia Tech, 1994-05-04)
The effectiveness of an adsorption filter in retaining bacteria present in milk was examined. Skim milk and whole milk (100ml) were separately filtered through a 47mm adsorption filter. No significant change in total solids, total fat, and solids-not-fat percentages of skim and whole milk permeates was observed after filtration. Adsorption of Pseudomonas fluorescens at target concentrations of 103 , 102 , and 101 cells/ml was determined in 100ml of dairy standard methods buffer, nutrient broth, whole milk, and skim milk. The average percentage bacterial retentions were 95 ± 5.5%, 95 ± 2.6%, 28 ± 22.1%, and 62 ± 15.5%, respectively. A treatment was developed for milk to increase the bacterial retention of ~ fluorescens after filtration. The preferred treatment for 100ml of skim milk involved the following final concentrations (v/v): 0.80% disodium ethylenediamine-tetraacetic acid, 0.02% sodium dodecyl sulfate, pH to 7.5 with 1N sodium hydroxide. The average bacterial retention of ~ fluorescens using the treatment was 91 ± 7.1%. Enumeration of bacteria adsorbed to the filter was then conducted using impedance microbiology. When milk was inoculated with ~ fluorescens at target concentrations of 103 , 102 , and 101 cells/ml, an average log bacterial increase of 1.4 ± 0.1 (25x) was obtained. This method will allow for rapid detection of microorganisms in milk by increasing microbial load in the tested sample and eliminating the need for pre-enrichment.
Clostridium difficile toxins A and B: exploring the possible mechanism of action
Jefferson, Kimberly Kay (Virginia Tech, 1995-01-05)
Clostridium difficile is a common cause of antibiotic-associated diarrhea and occasionally causes the life-threatening disease pseudomembranous colitis. The pathogenicity of the organism has been attributed to the production of two large exotoxins, toxin A (308,000 daltons) and toxin B (269,000 daltons). Toxin A is a powerful enterotoxin and is generally thought to play the more important role in the pathology of the disease. Toxin B may exert its effect after the initial tissue damage by toxin A. Both toxins cause rounding of mammalian culture cells by disrupting the cytoskeletal system. The similar biological activities and high percentage of sequence homology between the two toxins suggest that they have a similar mechanism of action. I found that purified preparations of both toxins cleave skeletal muscle actin at a single site, producing a 38,000 dalton actin fragment, and that the toxins are capable of autodigestion. The proteolytic activity may be involved in the mechanism of action of the toxins. I also analyzed an aberrant strain of C. difficile which reportedly lacked the gene for toxin B. Such a strain would be very useful for the study of the mechanism of toxin A. I concluded however, that the strain contained the genes for both toxin A and toxin B. The toxin genes and resulting proteins appear, however, to be slightly different from those of other strains.
Comparative Study of Semisynthetic Derivative of Natamycin and the Parent Antibiotic on the Spoilage of Shredded Cheddar Cheese
Suloff, Eric Charles (Virginia Tech, 1999-11-12)
The polyene macrolide antibiotic natamycin (Antibiotic A-5283) is commonly used to retard the growth of surface molds on various cheese varieties. Natamycin is commonly applied to the surface of cheese by dipping or spraying, using an aqueous dispersion containing 200 to 300 ppm of the additive. The large molecular weight of natamycin, 666 g/mol, and conjugated double bond structure causes it to be extremely insoluble in water and most food grade solvents. The inability to apply natamycin in true solution creates void non-treated areas on the food surface. These non-treated areas promote the growth of fungal organisms. A water soluble N-alkyl semisynthetic derivative of natamycin was synthesized by the Michael addition reaction of the parent with a N-substituted malemide. A comparative study investigating the effectiveness of the semisynthetic derivative of natamycin and the parent antibiotic in suppressing mold growth on one month aged shredded Cheddar cheese modified atmosphere packaged (MAP) was performed. A 20 ppm natamycin treatment effectively suppressed visible mold growth (<104 CFU/g) in MAP samples for up to 30 days after opening. The 20 ppm semisynthetic derivative performed similarly to the 10 ppm natamycin treatment in retarding mold growth. Visible mold growth did not occur for these treatments in MAP samples until 20 days after opening. Analysis of storage conditions revealed that an outgrowth of mold in shredded cheese occurred in MAP packages stored longer than 15 days. This bloom in mold growth was attributed to the degradation of natamycin and the semisynthetic derivative throughout storage. The stability and degradation of natamycin and the derivative were monitored throughout the study. Antibiotic concentration on the cheese surface was quantified by molecular absorption spectrometry. Results from this study showed, heavily contaminated samples caused the rate and loss of natamycin and the derivative to increase. Antibiotic concentration decreased at a similar rate in MAP and open package conditions. Natamycin and derivative were found to have similar degradation properties.
Culture enumeration, lactose hydrolysis and sensory changes in stored frozen yogurt fermented with two culture systems
Davidson, Richard H. (Virginia Tech, 1995-05-15)
The objective of this study was to compare products fermented with two culture systems to two endpoints for the following characteristics: survival of the culture bacteria, changes in protein, lactose and galactose concentrations and sensory changes. Frozen yogurt was produced using a standard lowfat ice cream mix formulation, fermented with supplemented and traditional culture systems, and stored for 11 weeks at -20°C. Three methods of recovery were employed: Bifid Glucose Agar with the Repair Detection System and Roll Tubes, Bifid Glucose Agar with the Repair Detection System on plates incubated in an anaerobe jar with a GasPak™, and Maltose/Galactose Reinforced Clostridial Agar incubated in an anaerobe jar with a GasPak™. Statistical analysis indicated that the Repair Detection System provided significantly (p<.05) enhanced recovery of Bifidobacterium longum. Recovery of B. longum on BGA Plates and M/G RCA plates was approximately one-half log lower than recovery on BGA in roll tubes. Culture bacteria in both systems survived at approximately 5x10⁶ cfu/mL during frozen storage. Lactose and protein levels showed no significant changes or differences between the two culture systems. Generally, galactose levels were significantly higher (p<.05) in the traditional culture system fermented to pH 5.6 compared to the supplemented system fermented to the same endpoint. The manufactured products (supplemented and traditional) were not different from the commercial product with respect to flavor intensity of yogurt flavor, vanilla, sweetness and freshness. Acid flavor was usually more intense when product was fermented to a pH of 5.6. The commercial product was more smooth than the manufactured products. Consumers indicated a “like slightly” to “like moderately” response for the supplemented and traditional inoculated frozen yogurts. The study concluded that the culture bacteria do survive the environment well enough to meet proposed standards of identity for frozen yogurt. The presence of probiotic bacteria in the supplemented system seemed to cause little to no difference in such attributes as protein and lactose levels, and sensory evaluation.
Determination of the Leak Size Critical to Package Sterility Maintenance
Keller, Scott Wayne (Virginia Tech, 1998-08-18)
This study was divided into four sections: the literature review; the mechanism by which a package defect becomes a leak; and the imposed pressures generated within a package during distribution; comparison of the threshold leak size to the critical leak size and their effect on loss of package sterility; and the relationships between microorganism characterisitics and the threshold leak size, and their effect on the critical leak size. Section II. The mechanism by which a package defect converts to a leaker in an effort to develop a relationship between the threshold leak size and loss of package sterility was studied. The threshold leak size is the hole size at which the onset of leakage occurs. The threshold pressure is that which is required to initiate a leak. Leak initiation was studied in terms of the interaction between three components: liquid attributes of liquid food products, defect size, and pressures required to initiate liquid flow. Liquid surface tension, viscosity, and density were obtained for sixteen liquids. The imposed pressures (Po) required to initiate flow through microtubes of IDs 0, 2, 5, 7, 10, 20 or 50 m, were measured using 63 test cells filled with safranin red dye, tryptic soy broth, and distilled water with surface tensions of 18.69 mN/m, 44.09 mN/m, and 64.67 mN/m, respectively. Significant differences were found between observed threshold pressures for safranin red dye, tryptic soy broth, and distilled water (p < 0.05). Liquids with small surface tensions such as safranin red dye required significantly lower threshold imposed pressures than liquids with large surface tensions such as distilled water (p < 0.05). An equation was developed to quantify the relationship between liquid surface tension, threshold imposed pressure, and defect size. Observed threshold pressures were not significantly different (p > 0.05) than those predicted by the equation. Imposed pressures and vacuums generated within packages during random vibration and sweep resonance tests were measured for brick-style aseptic packages (250 ml), metal cans size 76.2-mm x 114.3-mm (425 ml), quart gable top packages (946 ml), one-half gallon gable top packages (1.89 L) and one-gallon milk jugs (4.25 L). Significant differences were found between packages for observed generated pressures during vibration testing (p < 0.05). An equation to calculate the threshold like size based on liquid surface tension and imposed pressure was established. Section III. The onset of liquid flow through a defect as a result of imposed positive pressures or vacuum were linked to the sterility loss of a package. Five-hundred sixty-three test cells, each with microtubes of 0, 2, 5, 7, 10, 20 or 50 m, manufactured to simulate packages with defects, were biochallenged via an aerosol concentration of 106 cells/cm3 of Pseudomonas fragi Lacy-1052, under conditions of imposed positive pressure or vacuum of 20.7, 13.8, 6.9, 0, -6.9, -13.8, -20.7 kPa, respectively and temperatures of 4 , 25 and 37 C. A statistically significant relationship between loss of sterility due to microbial ingress in test cells and the initiation of liquid flow were found (p < 0.05). Microbial ingress was not found in test cells with microtube IDs of 2 m. Leak sizes critical to the sterility maintenance were found to be different based on the liquid surface tension, and imposed package pressures. The threshold leak size where the onset of liquid flow was initiated, and the critical leak size at which loss of sterility occured were not significantly different (p > 0.05). Section IV. The effects of microorganism size and motility, and the imposed pressure required to initiate liquid flow, on the leak size critical to the sterility of a package were measured. Pseudomonas fragi Lacy-1052, Bacillus atrophaeus ATCC 49337, and Enterobacter aerogenes ATCC 29007 were employed to indicate loss of package sterility. One hundred twenty-six microtubes with interior diameters (I.D.s) of 5, 10, and 20 m and 7 mm in length were used as the manufactured defects. Forty-two solid microtubes were used as a control. An equation was used to calculate imposed pressures sufficient to initiate the flow of tryptic soy broth through all defects. No significant differences were found for loss of sterility as a result of microbial ingress into test cells with microtube ID sizes of 5, 10, and 20 m between the test organisms (p > 0.05). Interactions between the initiation of liquid flow as a result of imposed pressures, and the sterility loss of test cells were significant (p < 0.05).
Effect of glycosidases and proteases on biofilms formed on black buna-N rubber
Clark, Patricia Maria (Virginia Tech, 1996-09-17)
Proteolytic enzymes and a glycolytic enzyme used in dishwashing detergents and by the starch conversion industry were examined for their ability to remove bacteria attached to black buna-N rubber. Pure culture and mixed culture biofilms of Pseudomonas fluorescens and Listeria monocytogenes were treated with the proteolytic enzymes Purafect® (Genencor International), Durazym™, and Savinase® and the glycolytic enzyme Termamyl® (Novo Nordisk BioChem North America). Compared to controls, none of the enzyme treatments were able to significantly remove P. fluorescens cells adherent in pure culture (p>0.05). Durazym™, Purafect®, and Termamyl® did significantly reduce the number of adherent cells of L. monocytogenes grown in pure culture. Treatment with Purafect® reduced the number of attached cells of both P. fluorescens and L. monocytogenes when grown in mixed culture. Material which absorbs at 280 nm was released from both pure and mixed culture biofilms when all three proteolytic enzymes were used. No survivors remained after planktonic (free floating) cells of both P. fluorescens and L. monocytogenes were incubated with Purafect®. Reduction in overall numbers of P. fluorescens and L. monocytogenes attached in mixed culture by Purafect® appeared to involve a combination of release of proteinaceous material followed by bactericidal effects on exposed cells.
Effect of hydrogen peroxide and other protease inhibitors on Cryptosporidium parvum excystation and in vitro development
Kniel, 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.
The effect of modified atmosphere packaging (MAP) on the shelf- life of refrigerated, cubed turkey thigh meat
Ahn, Insook (Virginia Tech, 1991-06-01)
This research was designed to investigate the effect of Modified Atmosphere Packaging (MAP) on the shelf life of refrigerated, cubed, turkey thigh meat. Modified atmospheres of 25% carbon dioxide and 75% nitrogen and 20% carbon dioxide, 60% oxygen, and 20% nitrogen were used for MAP1 and MAP2 respectively. All sample packages, MAPl, MAP 2 , and Air Control, were stored at O.5°C. Headspace gas analysis, color measurement, sensory evaluation, aerobic plate count, and oxidative deterioration of fat were examined over 21 day of storage. Microbiological spoilage was significantly delayed by modified atmosphere treatments. MAP1 delayed fat rancidity while MAP2 increased rancidity because of the high amount of oxygen. The redness of turkey thigh meat was increased in both MAPs. MAP2 showed the highest a values up to storage day 12 and then MAP1 had the highest a values on storage days 16 and 21. Sensory evaluations showed preferences for MAPs in all variables: color, appearance, and odor. ThUS, modified atmosphere treatment 1 (MAP1) demonstrated the best effect on the extension of the shelf life of turkey meat in this study.
Effect of modified atmosphere packaging on growth of Listeria monocytogenes and nonproteolytic Clostridium botulinum in cooked turkey
Lawlor, 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.
Effect of shelf-life and light exposure on acetaldehyde concentration in milk packaged in HDPE and PETE bottles
van Aardt, Marleen (Virginia Tech, 2000-02-11)
Poly(ethylene terephthalate) (PETE) packaging is becoming an increasingly popular choice of packaging material for milk, but has the disadvantage of releasing odorous acetaldehyde into food matrices. Sensory detection group thresholds for acetaldehyde in whole, low fat and nonfat unflavored milks were 3939, 4020, and 4040 ppb respectively with no significant difference due to fat level. Chocolate flavored milk and spring water showed detection thresholds levels for acetaldehyde of 10048 and 167 ppb respectively. This information assisted in determining if acetaldehyde migration from the package to the product would influence the flavor of the product. Whole milk was packaged in glass, high density polyethylene (HDPE), amber PETE, clear PETE, and clear PETE with UV light block and was exposed to fluorescent light of 1100-1300 lux (100-120 FC) at 4oC for 18 days. Sensory and chemical analysis and was done on milk from all containers over a period of 18 days. Emphasis was on oxidation, acetaldehyde and lacks freshness off-flavors and byproducts. All volatile flavor compounds studied (acetaldehyde, pentanal, dimethyl disulfide, and hexanal) were increased in light-exposed milk samples. Amber PETE showed the least amount of oxidation off-flavor, while clear PETE with UV block showed significantly less oxidation off-flavor than glass, clear PETE or HDPE on day 7 and 18. Acetaldehyde was not detected by sensory analysis in either light-exposed or light-protected samples. Chemical analysis showed relative acetaldehyde levels in glass (2220 ppb), HDPE (1265 ppb), amber PETE (3397 ppb), clear PETE (2930 ppb), and clear PETE with UV light block (1754 ppb) were all below concentrations found for human flavor threshold.
The Effectiveness of Potassium Lactate and Lactic Acid Against Campylobacter Species and Psychrotrophic Bacteria
Rasmussen, David Dean (Virginia Tech, 1999-09-16)
This study examined the efficacy of potassium lactate and lactic acid to control Campylobacter sp. and psychrotrophic bacteria on chicken. The objectives of the two studies conducted were to determine the optimal combination of potassium lactate and lactic acid to inhibit Campylobacter sp. in a challenge study and to inhibit naturally occurring Campylobacter sp. and psychrotrophic bacteria in a shelf life study. Boneless, skinless chicken breasts were injected with three levels of potassium lactate (0,1.5,2%), in conjunction with four levels of lactic acid. Lactic acid was injected (0, 0.1, 0.2, 0.3%) as well as applied directly to the surface (0.1% of weight of chicken breast). The chicken breasts were surface inoculated with a mixture of Campylobacter sp. and sampled over a period of 28 days at 11oC. The greatest inhibition was found using 2% potassium lactate in conjunction with any level of lactic acid (injected) or 0.1% lactic acid (surface application). Results of this study indicate that potassium lactate and lactic acid can be used to control the growth and/or survival of Campylobacter sp. on boneless chicken breasts. The second study eliminated the 1.5% potassium lactate and 0.2% and 0.3% lactic acid treatments and chicken breasts were not inoculated with Campylobacter sp.. This 4oC shelf life study occurred over 32 days, testing for Campylobacter species, psychrotrophic bacteria, as well as testing for sensory perceptions of color and odor changes in the chicken. The most effective treatment was the 2% potassium lactate-0.1% lactic acid surface treatment, demonstrating the most inhibition against both target populations. This treatment also had the greatest impact upon the odor of the chicken breasts. This treatment had the greatest difference from control samples, which was achieved by the inhibition of spoilage organisms on the chicken breasts.
Effects of massaging minced batter on the physical, chemical, and sensory characteristics of low-fat, high added water bologna
Gregg, Lori L. (Virginia Tech, 1992-02-28)
A high-fat bologna was formulated to contain 30%fat/10% added water (AW). Three low-fat treatments were formulated to contain 10%fat/30%AW. Lean and fat trim for the low-fat treatments (2, 3, and 4) were combined and minced before massaging intermittently (10 min on/20 min off) for 0, 2.5 and 5.0 h, respectively. Massaging improved (P<0.05) sensory cohesiveness scores and decreased particle definition. However, the high-fat control was the most cohesive, firmest and least juicy (P<0.05). Instron Texture Profile Analysis indicated that massaging increased cohesiveness (P<0.05) and tended to increase springiness. There were no differences (P>0.05) in hardness or fracturability among the low-fat treatments. The high-fat bologna was the hardest, least cohesive, and least springy P
Effects of UV Irradiation on the Reduction of Bacterial Pathogens and Chemical Indicators of Milk
Matak, 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.
Enhanced recovery of injured and noninjured cells of Bifidobacterium species from water and dairy products
Arany, 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 juices
Kniel, 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 Bluefish
Lorca, 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.
Formulating and Processing of a Nutritionally Enhanced Extended Shelf-Life Fluid Milk and Egg Mixture
Sutton, Tracy D. Jr. (Virginia Tech, 1997-10-02)
A milk and egg mixture was processed at 96C and 92C with 10 sec hold times and evaluated for nutritional composition, functional characteristics, and shelf-life. The process was more than sufficient to destroy Coxiella burnetti and Salmonella senftenberg which were the most heat resistant organisms of concern in processing this milk and egg mix. The spoilage organisms received 2,200 D and 425 D processes, respectively, which were more than adequate for providing a safe product and extending the shelf life of the product for seven weeks under refrigerated storage conditions. Both sweetened and unsweetened formulations were evaluated. The nutritional profile of the milk and egg mix was improved when dried eggs (solids and liquid proportion equivalent to whole egg) were replaced with dried egg white, cholesterol reduced egg yolk, and skim milk. The fat and cholesterol were reduced between 22 to 33% and 37 to 44%, respectively, in the cholesterol reduced formulation (CRF) as compared to the control formulation (CF). The protein content of the milk and egg mix was not altered by utilization of cholesterol - reduced egg yolk in the CRF as compared to the CF. Addition of beta-galactosidase decreased the lactose up to 96%. The CF were more yellow than the CRF in the mixes and baked gels (p< 0.05). There were also no difference in gel strength between the baked gels made from the two formulations. There were no significant chemical and physical changes over the seven week storage period of the product at refrigerated conditions (p< 0.05).
Growth and survival of Clostridium botulinum type E in pasturized oysters
Bucknavage, Martin M. (Virginia Tech, 1988-12-09)
The risk of toxin production by Clostridium botulinum type E in pasteurized oysters was evaluated. Thermal death time studies for type E spores in a oyster homogenate showed that the spores survived pasteurization at 550 C; D-values ranged from 65 to 100 min at 700 C and 880 to 1300 min at 550 C. When tubes of oyster homogenate were inoculated with 1x103 type E spores/ml and stored at 3, 6, 12, and 30oC, no growth was observed; however, when the inocculum was increased to 1x104 spores/ml, toxin was produced during storage at 30oC, but not at lower temperatures. For containers of whole oysters inoculated with a low spore level, toxin production occurred during incubation at 6, 12, and 30oC.

Browsing by Author "Hackney, Cameron Raj"

Results Per Page

Sort Options