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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
-
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
-
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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- Title
- An Integrated Cell Culture-PCR Assay for the Detection of Viable Coxiella Burnetii Nine Mile Phase II RSA 439 in Fluid Dairy Products
- Creator
- Kukreja, Ankush
- Date
- 2011-12, 2011-12
- Description
-
Coxiella burnetii, an obligate intracellular bacterium, has been used as the reference organism for defining milk pasteurization conditions....
Show moreCoxiella burnetii, an obligate intracellular bacterium, has been used as the reference organism for defining milk pasteurization conditions. With renewed interest in minimizing processing times and temperatures, and in ensuring product safety, development of an Integrated Cell Culture-PCR (ICC-PCR) assay may be useful for evaluating C. burnetii inactivation in fluid dairy products. The purpose of this research was to develop an ICC-PCR assay to determine viability and detection limit of C. burnetii and characterize inhibiting effects contributed by various milk formulations. Coxiella burnetii was inoculated on Vero cell culture with PBS and whole milk, incubated for 48 hours to allow infection, and then incubated for 11 days to allow propagation. The propagated C. burnetii mix was subjected to freeze-thaw followed by DNA extraction with Autogen Blood & Tissue DNA Extraction Kit using Quickgene Mini80. Extracted DNA was amplified using TaqMan-MGB based qPCR targeting published primers for the IS1111a transposase gene to verify C. burnetii growth/infectivity. For detection limit determination, serial dilutions of C. burnetii in RPMI were mixed separately in whole milk, cream, chocolate milk and eggnog. The mix was overlaid on sub-confluent Vero cell monolayers, subjected to freeze-thaw followed by DNA extraction using Autogen Blood & Tissue DNA Extraction Kit and PCR. Uninoculated wells were evaluated for dairy sample background signal, and inhibition was evaluated by comparison to purified DNA. Duplicate trials using 6 replicates per sample were performed.
M.S. in Food Safety & Technology, December 2011
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