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- Title
- LISTERIA MONOCYTOGENES SURVIVAL AND GROWTH IN FLAVORED MILKSHAKES MADE FROM NATURALLY-AND ARTIFICIALLY-CONTAMINATED ICE CREAM
- Creator
- Bathija, Vriddi Mahesh
- Date
- 2016, 2016-12
- Description
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Listeria monocytogenes is the causative agent of the disease listeriosis and was implicated in a multistate foodborne outbreak associated with...
Show moreListeria monocytogenes is the causative agent of the disease listeriosis and was implicated in a multistate foodborne outbreak associated with ice cream spread over four years from 2010 to 2014 in Kansas, Oklahoma, Texas and Arizona. Ten illnesses were reported during the course of this outbreak, resulting in 100% hospitalization and a mortality rate of 33%; the individuals who died in the outbreak had consumed milkshakes made with the contaminated ice cream. The ice cream was found to be contaminated uniformly at 10 MPN/g. This study assessed the growth kinetics of L. monocytogenes in milkshakes made with naturally- and artificially-contaminated ice cream, and with or without flavoring agents. Artificial-contamination of ice cream samples included inoculation with a cocktail of rifampicin-resistant L. monocytogenes into the middle of the product using a wide-orifice pipet tip. Milkshake were prepared with or without strawberry, chocolate, or mint flavoring, using the recipe associated with the healthcare facility where the illnesses occurred. Milkshakes were stored in sterile plastic cups at 10ºC and an asymmetric (3 tubes of 100ml, 5 tubes of 10 ml, 8 tubes of 1ml and 8 tubes of 0.1ml sampling scheme) most probable number (MPN) enumeration was conducted after 0, 12, 24, 48, 72, 96 and 144 h. The Baranyi model was used to model L. monocytogenes growth rates, maximum populations, and lag phases. Compared to milkshakes made with no flavoring agents, the milkshakes with flavoring resulted in decreased growth rates for L. monocytogenes for both contamination states; the lowest growth rate of the pathogen was observed in strawberry flavored milkshakes made from artificially-contaminated ice cream (0.029 log CFU/ml per hour). Chocolate and mint flavorings resulted in significantly (P < 0.05) longer lag phases for both natural (68.2 and 83.0 h) and artificial-contamination (47.7 and 54.2 h, respectively). The highest maximum population (5.79 log CFU/ml) was achieved by L. monocytogenes in naturallycontaminated milkshakes without any flavoring agent. Since challenge studies often depend on the artificial contamination of a food product, this study evaluated the differences between artificial and natural contamination of L. monocytogenes in milkshakes. The data obtained can be used for risk assessment purposes.
M.S. in Food Safety and Technology, December 2016
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- Title
- EFFICACY OF AQUEOUS INOCULATION IN LOW-WATER ACTIVITY MATRIX ON SALMONELLA ENTERICA SEROTYPE AGONA THERMAL RESISTANCE AND STABILITY DURING STORAGE
- Creator
- Liao, Li
- Date
- 2016, 2016-07
- Description
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Methods used to inoculate foods may impact the results of Salmonella survival and thermal resistance studies. Currently, there is little...
Show moreMethods used to inoculate foods may impact the results of Salmonella survival and thermal resistance studies. Currently, there is little information as to the most effective means to inoculate Salmonella into low-moisture food products for use in process validation studies. The objective of this study is to assess the resulting 42 d storage stability and thermal resistance of Salmonella inoculated by liquid addition in food and inert carrier matrices. Salmonella enterica serovar Agona 447967 was inoculated into ground pepper, oat flour, and sand at approximately 9-10 log CFU/g using a hand mixing procedure and stored at 25°C, 32% relative humidity (RH). After a 2 d equilibration, the samples were tested for inoculation homogeneity. Distribution of Salmonella populations proved uniform in black pepper and sand but not in oat flour. Subsequent testing for stability by enumeration with both tryptic soy agar with 0.6% yeast extract (TSAYE) and xylose lysine desoxycholate (XLD) agars was performed weekly with black pepper and sand only. Thermal resistance was determined periodically during storage using aluminum test cells for pepper and glass vial for sand as sample holders. Over 42 d, the average starting Salmonella populations in pepper and sand were 7.88 ± 0.13 and 7.69 ± 0.11 log CFU/g, respectively, and final populations were 6.14 ± 0.06 and 6.52 ± 0.07 log CFU/g, respectively. Population changes were significantly different (P < 0.05). For pepper the thermal resistance did not change significantly during storage (P > 0.05) and were similar to values reported by other researchers using alternative inoculation techniques. However, thermal resistance measured in sand (D90ᵒC = 3.39 ± 0.41 min) was substantially higher than that measured in black pepper (D75ᵒC-value = 4.99 ± 0.21 min) or other literature values. Overall a liquid inoculation protocol proved efficacious for small particles such as ground black pepper or sand but was unable to provide a uniform distribution of cell populations in a powder such as oat flour.
M.S. in Food Safety and Technology, July 2016
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- Title
- THERMAL INACTIVATION OF POLYPHENOL OXIDASE IN POTATO, AVOCODO AND APPLE
- Creator
- Banstola, Anunaya
- Date
- 2011-06, 2011-07
- Description
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Polyphenol oxidase (PPO) needs to be inactivated to control the enzymatic browning which is undesirable in fruits and vegetables industry....
Show morePolyphenol oxidase (PPO) needs to be inactivated to control the enzymatic browning which is undesirable in fruits and vegetables industry. Enzymes have substrateorigin- specificity, and thus the functionality and inactivation properties of PPO varies depending on the source of enzyme, properties of food matrix, method of treatment applied as well as measurement techniques. Therefore, the result from one food cannot be extrapolated to another food, and more research is needed to understand the behavior of PPO in different processing conditions. In this study, thermal inactivation of PPO in potato, avocado and apple was studied at four different temperatures (50, 60, 70 and 80 °C). The treatment time varied from 1 to 60 min, depending upon the temperature used. The level of inactivation was deduced by residual enzyme activity which was assayed by spectrophotometric methods in two different substrates, pyrocatechol and 3,4- dihydroxyphenylalanin (DOPA) using an ELISA plate reader. The degree of PPO inactivation achieved in potato and apple extracts was higher using pyrocatechol as the substrate than using DOPA, where it was similar for both substrates in case of avocado. Inactivation kinetics was studied in terms of rate constant k, D values and activation energy. The inactivation rate followed the first order kinetics and higher dependency on treatment time was observed at higher temperatures. Biphasic inactivation was observed in case of apple PPO, where activation of enzyme was observed at low temperature (50 °C). In conclusion, level of PPO inactivation was dependent on the degree of the thermal treatment, source of PPO and substrate used for enzyme determination.
M.S. in Food Safety and Technology, July 2011
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