MICROBIAL MODELING AND BIOINFORMATICS FOR FOOD SAFETY AND SECURITY
Location: Residue Chemistry and Predictive Microbiology
Title: MODELING THE SURVIVAL OF ESCHERICHIA COLI O157:H7, LISTERIA MONOCYTOGENES AND SALMONELLA TYPHIMURIUM DURING FERMENTATION, DRYING, AND STORAGE OF SOUDJOUK-STYLE FEREMENTED SAUSAGE
Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 2, 2008
Publication Date: February 1, 2009
Citation: Hwang, C., Porto Fett, A.C., Juneja, V.K., Ingham, S., Ingham, B., Luchansky, J.B. 2009. Modeling the survival of escherichia coli o157:h7, listeria monocytogenes and salmonella typhimurium during fermentation, drying, and storage of soudjouk-style feremented sausage. International Journal of Food Microbiology. 129:244-252.
Interpretive Summary: Foodborne illnesses have been linked to the consumption of fermented dry and semi-dry sausage (FDSS). The Food Safety and Inspection Service of USDA requires that FDSS producers to validate that their manufacturing processes would produce products that meet the food safety requirements. Due to the lack of resources to conduct microbiological studies, many small and very small FDSS producers are unable to determine whether their processes meet the regulatory requirements. This study quantified and modeled the survival of three foodborne pathogens, Escherichia coli O157:H7, Listeria monocytogenes and Salmonella typhimurium in fermented sausages during fermentation and drying to various product acidities (pH 4.6-5.2) and moisture contents (water activity 0.86-0.92) and stored at various temperatures (4, 12, and 30 C). Results showed the pathogens died off in sausage to different extent during fermentation. Drying sausages of pH 5.2-4.6 to aw 0.92-0.86 resulted in additional reductions of pathogen. During storage the reductions of the three pathogens were higher in sausages with lower pH, lower aw and stored at higher temperatures. Using data and models from this study, FDSS producers could estimate the levels of pathogens that would be reduced in sausages with their manufacturing processes and modify the processes or adopt additional food safety measurements to meet the regulatory requirements.
Outbreaks of foodborne illnesses have been linked to the consumption of fermented dry and semi-dry sausage (FDDS) contaminated with E. coli O157:H7 and Salmonella spp. This study quantified and modeled the survival of E. coli O157:H7, L. monocytogenes and S. typhimurium in soudjouk-style sausage during fermentation, drying and storage. Soudjouk-style sausage batter was prepared from ground beef (20% fat), seasonings, starter culture and dextrose, and inoculated with a multi-strain mixture of E. coli O157:H7, L. monocytogenes, or S. typhimurium to an inoculum of ca. 6.5 log10 CFU/g in the batter. The sausages were sequentially fermented to pH values of ca. 5.2, 4.9 or 4.6, then dried to aw values of ca. 0.92, 0.89 or 0.86, and stored at 4, 21 or 30 degree C for up to 60 days. The levels of reduction of the three pathogens in the sausages during fermentation, drying and storage were determined and modeled as a function of sausage pH, aw and/or storage temperature. During fermentation to pH between 5.2 and 4.6, the cell reductions ranged from 0.02 to 0.91 log10 CFU/g for E. coli O157:H7, 0.10 to 0.43 log10 CFU/g for L. monocytogenes, and 0 to 2.24 log10 CFU/g for S. typhimurium. Drying sausages of pH 5.2-4.6 to aw of 0.92-0.86 resulted in reductions that ranged from 0.02 to 3.50 log10 CFU/g for E. coli O157:H7, 0 to 0.43 log10 CFU/g for L. monocytogenes, and 0.30 to 2.36 log10 CFU/g for S. typhimurium. During storage at 4, 21 or 30 deg C the reduction rates of the three pathogens were generally higher in sausages with lower pH, lower aw and stored at higher temperatures. Polynomial equations were developed to describe the reduction of the three pathogens during fermentation, drying and storage. The applicability of the resulted models for fermented sausage was evaluated by comparing model predictions with published data. Pathogen reductions estimated by the fermentation and storage models for E. coli O157:H7 and S. typhymurium were comparable to a high percentage of published data. Results of pathogen reductions from this study may be used as a reference for manufacturers of soudjouk-type sausages to adopt manufacturing processes that meet the safety requirements, and the models may be used for estimating the survival of E. coli O157:H7 and S. typhymurium in FDSS during fermentation and storage.