Modeling the survival of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium during fermentation, drying, and storage of soudjouk-style fermented sausage

This study quantified and modeled the survival of Escherichia coli O157:H7, Listeria monocytogenes and Salmonella Typhimurium in soudjouk-style fermented sausage during fermentation, drying, and storage. Batter prepared from ground beef (20% fat), seasonings, starter culture, and dextrose was separately inoculated with a multi-strain mixture of each pathogen to an initial inoculum of ca. 6.5 log10 CFU/g in the batter. The sausages were subsequently fermented at 24 °C with a relative humidity (RH) of 90% to 95% for 3 to 5 days to ca. pH 5.2, pH 4.9 or pH 4.6, then dried at 22 °C to aw 0.92, aw 0.89, or aw 0.86, respectively, and then stored at 4, 21, or 30 °C for up to 60 days. Lethality of the three pathogens was modeled as a function of pH, aw and/or storage temperature. During fermentation to pH 5.2 to pH 4.6, cell reductions ranged from 0 to 0.9 log10 CFU/g for E. coli O157:H7, 0.1 to 0.5 log10 CFU/g for L. monocytogenes, and 0 to 2.2 log10 CFU/g for S. Typhimurium. Subsequent drying of sausages of pH 5.2 to pH 4.6 at 22 °C with 80% to 85% RH for 3 to 7 days to aw of 0.92 to aw 0.86 resulted in additional reductions that ranged from 0 to 3.5 log10 CFU/g for E. coli O157:H7, 0 to 0.4 log10 CFU/g for L. monocytogenes, and 0.3 to 2.4 log10 CFU/g for S. Typhimurium. During storage at 4, 21, or 30 °C the reduction rates of the three pathogens were generally higher (p < 0.05) in sausages with lower pH and lower aw that were stored at higher temperatures. Polynomial equations were developed to describe the inactivation of the three pathogens during fermentation, drying, and storage. The applicability of the resulting models for fermented sausage was evaluated by comparing model predictions with published data. Pathogen reductions estimated by the models for E. coli O157:H7 and S. Typhimurium were comparable to 67% and 73% of published data, respectively. Due to limited published data for L. monocytogenes, the models for L. monocytogenes would need additional validations. Results of pathogen reductions from this study may be used as a reference to assist manufacturers of soudjouk-style sausages to adopt manufacturing processes that meet the regulatory requirements. The resulting models may also be used for estimating the survival of E. coli O157:H7 and S. Typhimurium in other similar fermented sausage during fermentation and storage.