A THERMAL RESISTANCE STUDY OF SHIGA TOXIN-PRODUCING ESCHERICHIA COLI (STEC) IN LOW MOISTURE FOOD WITH THE USE OF A DIFFERENTIAL SCANNING CALORIMETER (DSC)

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Description

According to CDC's Foodborne Disease Outbreak Surveillance System database, from the years 2007-2011, there were eight outbreaks associated with low-moisture food including nuts, cheese, cookie dough, and wheat snack food involving Shiga toxinproducing Escherichia coli O157:H7 (STEC), which led... Show moreAccording to CDC's Foodborne Disease Outbreak Surveillance System database, from the years 2007-2011, there were eight outbreaks associated with low-moisture food including nuts, cheese, cookie dough, and wheat snack food involving Shiga toxinproducing Escherichia coli O157:H7 (STEC), which led to over 318 cases of foodborne illnesses. Yet, insufficient data on STEC thermal inactivation has been obtained in lowmoisture food. In this study, a novel methodology using a Differential Scanning Calorimeter was used to measure STEC thermal inactivation kinetics in low moisture environments. The objective of this study was to use a Differential Scanning Calorimeter to measure D- and z-values, and therefore to determine the microbial thermal resistance, of select STEC strains. Five strains of outbreak related E. coli O157:H7 and one strain of E. coli K12 were individually grown on tryptic soy agar with 0.6% yeast extract (TSAYE). The cells were harvested and inoculated into sample matrices. Matrices included a moist buffered peptone water solution, a simple model low-moisture food matrix (corn syrup), and lowmoisture food (oat flour and peanut butter). Samples were individually heated using a Differential Scanning Calorimeter (DSC). The DSC was able to achieve a reproducible and accurate thermal environment. Following heat treatment, microbial survivors were enumerated via a traditional plate counting method. The six strains showed greater thermal resistance in corn syrup than in a buffered solution and in peanut butter and oat flour compared with both the corn syrup or buffer solution (p < 0.05). At the same processing condition linearly rising temperature at 5oC/min, in low moisture food matrices, approximately 90oC and 95oC was needed to reduce the outbreak strains of STEC in peanut butter and oat flour by 5-log CFU/g; whereas 85oC and 75oC were needed for corn syrup and buffer solution, respectively. D65 o C ranged from 0.26-0.92 min for all strains tested in buffer. Those same strains exhibited a 10-100 times increase in resistance in corn syrup (D65 o C = 2.6-108.6 min). The measurement that quantifies the increased heat resistance of STEC in low moisture food will improve science-based risk reduction by ensuring process lethality in these types of food.
M.S. in Food Safety and Technology, December 2014 Show less

Details
Department

NCFST / National Center for Food Safety and Technology

Title

A THERMAL RESISTANCE STUDY OF SHIGA TOXIN-PRODUCING ESCHERICHIA COLI (STEC) IN LOW MOISTURE FOOD WITH THE USE OF A DIFFERENTIAL SCANNING CALORIMETER (DSC)

Institution

Illinois Institute of Technology

Creator(s)

Liu, Shi

Advisor(s)

Zhang, Wei

Date

2014
2014-12

Description

According to CDC's Foodborne Disease Outbreak Surveillance System database, from the years 2007-2011, there were eight outbreaks associated with low-moisture food including nuts, cheese, cookie... Show moreAccording to CDC's Foodborne Disease Outbreak Surveillance System database, from the years 2007-2011, there were eight outbreaks associated with low-moisture food including nuts, cheese, cookie dough, and wheat snack food involving Shiga toxinproducing Escherichia coli O157:H7 (STEC), which led to over 318 cases of foodborne illnesses. Yet, insufficient data on STEC thermal inactivation has been obtained in lowmoisture food. In this study, a novel methodology using a Differential Scanning Calorimeter was used to measure STEC thermal inactivation kinetics in low moisture environments. The objective of this study was to use a Differential Scanning Calorimeter to measure D- and z-values, and therefore to determine the microbial thermal resistance, of select STEC strains. Five strains of outbreak related E. coli O157:H7 and one strain of E. coli K12 were individually grown on tryptic soy agar with 0.6% yeast extract (TSAYE). The cells were harvested and inoculated into sample matrices. Matrices included a moist buffered peptone water solution, a simple model low-moisture food matrix (corn syrup), and lowmoisture food (oat flour and peanut butter). Samples were individually heated using a Differential Scanning Calorimeter (DSC). The DSC was able to achieve a reproducible and accurate thermal environment. Following heat treatment, microbial survivors were enumerated via a traditional plate counting method. The six strains showed greater thermal resistance in corn syrup than in a buffered solution and in peanut butter and oat flour compared with both the corn syrup or buffer solution (p < 0.05). At the same processing condition linearly rising temperature at 5oC/min, in low moisture food matrices, approximately 90oC and 95oC was needed to reduce the outbreak strains of STEC in peanut butter and oat flour by 5-log CFU/g; whereas 85oC and 75oC were needed for corn syrup and buffer solution, respectively. D65 o C ranged from 0.26-0.92 min for all strains tested in buffer. Those same strains exhibited a 10-100 times increase in resistance in corn syrup (D65 o C = 2.6-108.6 min). The measurement that quantifies the increased heat resistance of STEC in low moisture food will improve science-based risk reduction by ensuring process lethality in these types of food. Show less

Type

Thesis

File type

application/pdf

Access

Restricted Access

Rights

In Copyright
http://rightsstatements.org/page/InC/1.0/

Identifier

http://hdl.handle.net/10560/3441

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