Risk-based control and management of Listeria monocytogenes and Salmonella spp. in short- and long-maturated Italian fermented sausages

OBJECTIVES Although fermented foods are generally recognized as safe, some notable outbreaks of foodborne illness associated with fermented foods have occurred. The extent to which fermented foods are safe and how fermentation processes should be conducted to achieve a required level of safety are critical questions. Depending on manufacturing conditions, foodborne pathogens may survive at the end of the process. Therefore, the objective of this study was to evaluate the risk that Listeria monocytogenes and Salmonella spp. pose to the consumer at the time of consumption of Cacciatore and Felino sausages and to demonstrate how the results can be used to manage the risks by setting Performance Objectives (PO) and/or Performance Criteria (PC) during manufacturing of these products to achieve a suggested Food Safety Objective (FSO). METHODS Cacciatore and Felino batter was inoculated with a cocktail of L. monocytogenes or Salmonella spp. strains (ca. 10^5-10^6 cfu/g) and their survival was monitored at specific time points during sausages manufacturing. For each pathogen and sausage, four (4) different batches (replicates) were prepared at different times. Cacciatore has short maturation time (20 days) whereas Felino ripening lasts up to 40 days (long maturation time). Various models were tested and the best model was selected, based on several statistical indices to calculate the parameters of interest (inactivation rate, kmax in day-1; and time needed for 1 log reduction of the pathogen, D-value in days). 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. The results were used to provide examples for risk management of fermented sausages. RESULTS The inactivation of L. monocytogenes and Salmonella spp. in both sausages was log-linear. Inactivation of L. monocytogenes during manufacturing of Cacciatore (kmax=0.04, D-value=52) and Felino (kmax=0.02, D-value=111) was negligible (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) and pH (0.003) in Cacciatore (50% of explained variance). A part (10-15%) of the remaining unexplained variance was attributed to the applied temperature. The ICMSF equation (2002) was used to make implications about the PO and PC for controlling pathogens in both sausages. CONCLUSIONS AND IMPACT OF THE STUDY 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. Aw 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. Although, raw materials quality constitutes a critical control point, the safety of these products is almost totally dependent on proper fermentation-ripening (killing step). Pathogens should be below certain levels at specific process stages (initial contamination level and inactivation during fermentation-ripening) to meet a FSO.