Survival of Listeria monocytogenes and Salmonella spp. in Cacciatore and Felino, two Italian fermented sausages representing short- and long- ripening times

Fermented sausages are generally considered safe. However, some notable outbreaks associated with fermented foods have occurred. Depending on manufacturing conditions, foodborne pathogens may survive at the end of the process. Moreover, foodborne pathogens may adapt to the dynamically changing environment of the fermented sausages allowing better survival. The objective was to evaluate the survival potential of Listeria monocytogenes and Salmonella spp. in Cacciatore (fermentation-ripening 20 days) and Felino (fermentation-ripening 40 days) fermented sausages. Sausages batter was inoculated with a five-strains cocktail of L. monocytogenes or Salmonella spp. (approximately 10^5-10^6 cfu/g) and their survival was monitored at specific time points during sausages manufacturing. For each pathogen and sausage, four different batches were prepared at different times. Kinetic parameters (inactivation rate, kmax in day-1; and time needed for 1 log reduction of the pathogen, D-value in days) were calculated after fitting kinetic behavior models and selecting the best model based on statistical indices. Model fitting was performed using GraphPad Prism 5. Significant factors (pH and aw) for L. monocytogenes and Salmonella spp. inactivation were assessed by multiple regression using SPSS v15.1. L. monocytogenes and Salmonella spp. survival in both sausages followed a log-linear trend. Inactivation of L. monocytogenes during manufacturing of Cacciatore (kmax=0.04, D-value=52) and Felino (kmax=0.02, D-value=111) was relatively small (only 0.4 log cfu/g). On the other hand, Salmonella spp. displayed faster inactivation (kmax=0.13 and 0.09, D-value=18 and 24, total inactivation=1.1 and 1.6 log cfu/g for Cacciatore and Felino, respectively). Multiple regression showed that aw was a significant parameter (p<0.05) for Salmonella spp. inactivation in both products, explaining 60-70% of the variance observed in the data. For L. monocytogenes, aw was significant (p=0.002) during its inactivation in Felino (40% of explained variance) whereas pH (p=0.003) during its inactivation in Cacciatore (50% of explained variance). A part (10-15%) of the remaining unexplained variance was attributed to the applied temperature. Salmonella spp. proved to be more sensitive than L. monocytogenes. Both pathogens, however, survived relatively well as result of the conditions (pH, aw and fermentation temperature) prevailing during manufacturing of the sausages. Water activity proved to be a key factor. Quantitative analysis of the data originating from challenge tests may provide critical information on which combinations of the process parameters would potentially lead to better control of the pathogens. Moreover, the analysis clearly identified factors that need to be validated experimentally, i.e. Felino characteristics lie within the range that may support growth of L. monocytogenes according to EC regulation 2073/2005 and its amendment 1441/2007.