Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Food Science and Technology

Major Professor

Faith Critzer

Committee Members

Doris H. D'souza, Mark T. Morgan


Foodborne pathogens such as Listeria monocytogenes, Salmonella enterica, and Shiga-toxigenic Escherichia coli (STEC) are consistently an issue for food safety. Controlling and preventing the spread of these pathogens is paramount for food processors. In January of 2001, the Food and Drug Administration (FDA) implemented mandatory hazard analysis critical control points (HACCP) for juice manufactures to prevent the number of foodborne illnesses related to juice outbreaks that were increasingly frequent. Juice HACCP does not require traditional pasteurization of juice with heat but does require juice processors achieve a 5-log pathogen reduction of any pertinent foodborne pathogens.It is important to validate any process to assure consistent lethality when processing. Microorganisms, including foodborne pathogens, when given enough time and nutrients can adapt to a wide variety of environments (e.g. low pH, desiccation) in food production. These adaptations may confer a competitive advantage when confronted with environmental stressors. To that end, it is important to understand what role, if any, acid adaptation may play in thermal inactivation rates of foodborne pathogens.The thermal inactivation rates of Salmonella and STEC cocktails were determined for three different temperatures (60°C, 65°C and 70°C) with prior acid adaptation through two different mechanisms (hydrochloric acid and glucose supplementation) as well as a control. In a similar fashion, inactivation rates of L. monocytogenes were determined for these treatments at 60°C and 70°C. The thermal death time curves were compiled from the observations of six independent replicates and evaluated for fit using linear and Weibull regression models, with Weibull models resulting in a better fit (R2>0.925). Overall, STEC cocktail was the most thermally resistant, and acid adaptation did not impact thermal resistance.

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