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VALIDATION OF BAKING TO INACTIVATE SALMONELLA IN HIGH-PROTEIN AND HIGH-FAT MODEL FOODS
Title
VALIDATION OF BAKING TO INACTIVATE SALMONELLA IN HIGH-PROTEIN AND HIGH-FAT MODEL FOODS
Creator
Wang, Wenqian
Date
2017, 2017-07
Description
Baked food products, such as dry pet foods, undergo changes of temperature and water activity (aw) during forced hot air processes. As one of...
Show moreBaked food products, such as dry pet foods, undergo changes of temperature and water activity (aw) during forced hot air processes. As one of the most thermal resistant microorganisms in low-moisture/intermediate moisture foods, Salmonella’s thermal inactivation kinetics during these processes is not well understood and difficult to predict. The objective of this study was to evaluate thermal inactivation kinetics of Salmonella enterica serovar Agona 447967 in model high-protein (HP) and high-fat (HF) multiple-component foods baked in a laboratory-scale oven, as influenced by oven temperature and relative humidity (RH). Model high-protein and high-fat foods, formulated with wheat flour, soy protein and soy oil, were inoculated with Salmonella Agona to a level of ~9 log CFU/g, and mixed to form a homogenous dough. Dough samples (57 mm diameter x 6 mm thick) were baked (3 samples per dwell time, 6 dwell times per condition) in a lab-scale oven at 120°C (10% RH) and 85°C (20%, 35% RH, 50% RH), respectively. Temperature and aw were measured at the surface and geometric center of the product during baking. Processed samples were collected in sterile bags and immediately cooled in an ice-water bath. Salmonella was enumerated on trypticase soy agar supplemented with yeast extract and incubated at 37°C for 24 h. Similar reductions (p>0.05) of 5.12-, 5.11-, 4.55-, and 4.78-log CFU/g were achieved after 40 min at 120°C/10% RH, 90 min at 85°C/20% RH, 50 min at 85°C/35% RH, 8 min at 85°C/50% RH, respectively, in the high-protein model food. Similar results were achieved in the high-fat matrix. The aw at the geometric center of the product (initially at aw =0.98) did not change appreciably during baking, while the aw at the product surface, the location of least lethality, decreased significantly (p<0.05) during baking; the decreases were more pronounced at lower oven RH. The results indicate that thermal inactivation of Salmonella Agona was driven by temperature and relative humidity in the oven. Higher temperature and higher relative humidity level led to greater Salmonella inactivation.
M.S. in Food Process Engineering, July 2017
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THE EVALUATION OF THERMAL INACTIVATION OF COXIELLA BURNETII NINE MILE PHASE II IN BOVINE AND NON-BOVINE MILKS BY MOST PROBABLE NUMBER-POLYMERASE CHAIN REACTION (MPN-PCR) ASSAY
Title
THE EVALUATION OF THERMAL INACTIVATION OF COXIELLA BURNETII NINE MILE PHASE II IN BOVINE AND NON-BOVINE MILKS BY MOST PROBABLE NUMBER-POLYMERASE CHAIN REACTION (MPN-PCR) ASSAY
Creator
Zhang, Cheng
Date
2016, 2016-05
Description
As non-bovine milks become popular for human consumption, ensuring that standard bovine milk pasteurization conditions provide enough...
Show moreAs non-bovine milks become popular for human consumption, ensuring that standard bovine milk pasteurization conditions provide enough treatment for non-bovine milks is significant for food safety. Coxiella burnetii, an obligate intracellular bacterium, has been used as the reference microorganism for defining milk pasteurization conditions. To evaluate C. burnetii thermal inactivation in bovine and non-bovine milks at commercial pasteurization temperature, an MPN-PCR assay was developed to quantitate viable C. burnetii in milk. Using this assay, the thermal inactivation of C. burnetii and a potential nonpathogenic surrogate, Micrococcus luteus, was tested in bovine, buffalo, camel and goat milks. Milk in sealed glass vials was pre-heated in a water bath at 72°C and inoculated via a syringe with C. burnetii and M. luteus at a final concentration of ~6.5 log10 ge/mL (CFU/mL) each. The inoculated milk was heat-treated at 72°C for up to 16 sec, cooled in a crushed ice bath and serially diluted. Viable M. luteus was quantitated by plating on BHIA plates. For C. burnetii detection, 1 mL of each dilution was inoculated into 9 mL Acidified Citrate Cysteine Medium-2 (ACCM-2) in triplicate T-25 flasks to produce a 3- flask Most Probable Number (MPN) assay. Viability of C. burnetii was considered positive if an increase of ≥0.5 log10 ge/mL was detected by qPCR after 14 d growth in ACCM-2 media. The numbers of positive flasks at each dilution were used to calculate the remaining viable C. burnetii by MPN method. The average D-values for 72°C inactivation were 1.99 ± 0.21 sec, 0.79 ± 0.28 sec, 1.43 ± 0.30 sec, and 2.06 ± 0.71 sec for C. burnetii, and 5.47 ± 0.94 sec, 3.65 ± 0.45 sec, 3.48 ± 0.83 sec and 5.34 ± 1.54 sec for M. luteus in bovine, buffalo, camel and goat milks, respectively. For C. burnetii, D-values in camel and goat milks were not significantly different (p>0.05) from bovine milk, but the D-value in buffalo milk was significantly lower (p<0.05). These results indicate that non-bovine milks may not be a safety concern under standard milk pasteurization conditions, and M. luteus could be a good surrogate for C. burnetii thermal inactivation in milk.
M.S. in Food Safety and Technology, May 2016
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