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ENRICHMENT OF COXIELLA BURNETII FROM BOVINE AND NON-BOVINE MILKS USING AN AXENIC LIQUID CULTURE MEDIUM
Title
ENRICHMENT OF COXIELLA BURNETII FROM BOVINE AND NON-BOVINE MILKS USING AN AXENIC LIQUID CULTURE MEDIUM
Creator
Shi, Manman
Date
2016, 2016-07
Description
Non-bovine milks are becoming more popular as beverages and for making cheeses, however little are understood regarding how pathogens are...
Show moreNon-bovine milks are becoming more popular as beverages and for making cheeses, however little are understood regarding how pathogens are inactivated in these milks during pasteurization. Recently, a tissue culture-PCR method has been developed to quantify inactivation of Coxiella burnetii, the obligate intracellular bacterium which is the reference pathogen for milk pasteurization. Unfortunately, this method is time-consuming and quite laborious. A potential improvement over the ICC-PCR method may be the use of a new specialized liquid medium which has been shown to allow growth of pure cultures of C. burnetii outside of host cells. In this study, ACCM-2 was evaluated for its’ ability to enrich C. burnetii from bovine and non-bovine milks as a potential alternative to tissue culture enrichment for Most Probably Number (MPN) quantification of inactivation of C. burnetii in milks. C. burnetii in bovine whole milk and cream (as a surrogate for a high fat product), camel, water buffalo, and goat milk were grown in ACCM-2 media (1:10) in 10 mL volumes in T-25 flasks at 37 °C under 5% CO2 and 2.5% O2 with sampling over 14 days. C. burnetii levels were determined by quantitative PCR (qPCR) against a standard curve for the Coxiella-specific IS1111a gene. C. burnetii in all milks grew at least 3 logs over 10 days with the exception of the water buffalo milk which did not allow growth. Bovine milk allowed the least growth and additional studies determined that the detection limit for growth of C. burnetii from this milk is about 6 ge/mL. Additional studies showed that adjustment of the pH from ~5.0 to 4.75 results in much improved growth of C. burnetii from bovine milk. Adjustment of pH did not allow growth from water buffalo milk, however additional dilution of the milk did allow improved C. burnetii growth but the added dilution also decreases the detection limit of the proposed new MPN-PCR assay. Further studies were completed to determine how thermal injury affects recover and growth of Coxiella burnetii in ACCM-2 media after thermal processing at 64 °C for up to 8 minutes. Although injury did increase the lag phase period and reduce the log phase growth rate from these samples, recovery and growth of at least 0.5 log was possible from all samples indicating that this media should be useful as an alternative enrichment method for use in an MPN format for quantification of thermal inactivation of C. burnetii in both bovine and non-bovine milks.
M.S. in Food Safety and Technology, July 2016
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H1 LUBRICANT TRANSFER FROM A HYDRAULIC PISTON FILLER INTO A SEMI-SOLID FOOD SYSTEM
Title
H1 LUBRICANT TRANSFER FROM A HYDRAULIC PISTON FILLER INTO A SEMI-SOLID FOOD SYSTEM
Creator
Chao, Pin-Chun
Date
2020
Description
The machinery used to prepare, and process food products need grease and oil for the lubrication of machine parts. H1 (food-grade) lubricants...
Show moreThe machinery used to prepare, and process food products need grease and oil for the lubrication of machine parts. H1 (food-grade) lubricants commonly used in the food industry are regulated as indirect additives by the FDA because they may become components of food through transfer due to incidental contact between lubricants and foods. The maximum level of H1 lubricants currently permitted in foods is 10 ppm, which was derived from FDA data gathered over 50 years ago. Although modern equipment has been designed to minimize the transfer of lubricants during processing and packaging, incidental food contact can still occur resulting from leaks in lubrication systems or over-lubrication. However, there is a lack of data for the FDA to evaluate and determine whether safety issues in the aspect of chemical contamination should be addressed concerning the use of food-grade lubricants in the production of foods. This research was conducted to determine the transfer of an H1 lubricant (Petrol-Gel) into a semi-solid model food from a hydraulic piston filler during conventional operating conditions at 25°C and 50°C. Xanthan gum solutions with concentrations of 2.3% at 25°C and 1.9% at 50°C were used to simulate the viscosity of ketchup at 50°C (970 cP). Petrol-Gel H1 lubricant with a viscosity grade of 70 cSt at 40°C was selected and the aluminum (Al) in the lubricant was targeted as a tracer metal. Analytical methods to quantify Al in both Petrol-Gel and xanthan gum solutions were successfully developed and validated by using inductively coupled plasma – mass spectrometry (ICP-MS) combined with microwave-assisted acid digestion technique. The concentration of Al in the Petrol-Gel was determined to be 3103 ± 26 μg/g. A total of 1.35 g of Petrol-Gel was applied to four ring gaskets in the filler, and 50 g samples of xanthan gum solution were collected into a 100-mL polypropylene tube (DigiTube) with low leachable metals during 500 filling cycles (the full capacity of the piston filler hopper).Results showed that the concentrations of Petrol-Gel transferred into 2.3% xanthan gum solution at 25°C ranged from 1.6 to 63.5 μg/g. A total of 64.47 mg of the applied Petrol-Gel (1.35 g) was transferred into 25 liters of the solution. The average concentration of Petrol-Gel in 2.3% xanthan gum solution was calculated to be 2.84 μg/g, which was lower than the current regulatory limit of 10 ppm. In general, the transfer of Petrol-Gel during the first 100 filling cycles was higher at 50°C than at 25°C. The concentration of Petrol-Gel transferred into 1.9% xanthan gum solution at 50°C for the first 100 filling cycles ranged from 1.6 to 35.06 μg/g and was 6.37 μg/g on average. This research will help FDA to calculate more realistic limits of the H1 lubricants permissible in foods at modern food processing conditions as well as estimate consumer dietary exposure to these indirect food additives.
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