Date of Award

5-2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Food Science and Technology

Major Professor

Doris H. D'Souza

Committee Members

Frances A. Draughon, P. Michael Davidson, Alan G. Mathew, Gina M. Pighetti

Abstract

The increase in Salmonella enterica outbreaks calls for an urgent need to rapidly detect and control Salmonella-associated contamination. Loop-mediated isothermal amplification (LAMP) assay is a novel method that can be completed within 90 min in a simple waterbath. Detection is by simple turbidity, fluorescence, or gel electrophoresis and is more specific than PCR. Reverse-transcriptase LAMP (RT-LAMP) targeting mRNA for the potential detection of live infectious Salmonella or recent contamination was used in this study and detection sensitivity to culture-based detection and RT-PCR assays was compared in pure culture, food products, and food processing environments. Our results showed detection limits of 101 and 102 CFU/ml for S. Typhimurium and 106 and 107 CFU/ml for S. Enteritidis by RT-PCR and RT-LAMP assays, respectively. Both assays targeted the specific Salmonella invA gene. Enrichment of 10 h was required for equivalent detection to culture-based methods for S. Typhimurium in pork products and 16 h for S. Enteritidis in liquid whole egg (LWE). For natural LWE and pork samples, 4-h non-selective enrichment followed by 16-h selective enrichment is recommended to ensure sensitive detection.

Effective inactivation/control measures for foodborne pathogens include high intensity ultrasound (HIU, an attractive non-thermal microbial inactivation process). HIU is gaining popularity due to its low cost that also maintains product sensory and functionality attributes. The efficiency of HIU (20 kHz) for Salmonella inactivation alone or in combination with nisin (a broad range bacteriocin), in a food model (liquid whole egg, LWE) was studied. Significant S. Enteritidis reduction of 3.6 log CFU/ml in pure culture and 1.4 log CFU/25 ml in LWE were obtained after HIU treatment alone for 10 min (P<0.05). Scanning electron micrographs revealed microbial structural damage after 5-min HIU. After 10-min HIU, LWE color became visually and instrumentally lighter along with a lower measured viscosity. However, no additional or synergistic antimicrobial effect was observed with nisin (100 and 1000 IU/ml) in combination with HIU. HIU shows great promise as an alternative non-thermal inactivation process for liquid foods. For use in hurdle approaches, further research on HIU combinations with other natural or generally recognized as safe antimicrobials is needed.

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