Abstract

This study investigated the behavior of Salmonella Typhimurium ATCC 14028, Escherichia coli O157:H7 and Listeria monocytogenes ATCC 13932 during the ripening of ‘Nduja, a traditional spreadable fermented sausage for which quantitative microbiological data remain limited. An experimental challenge test was conducted under pilot-plant conditions simulating artisanal production, with products inoculated with the three pathogens and monitored over a 28-day ripening period. Microbiological analyses were performed at defined time points, alongside pH and water activity measurements, and inactivation kinetics were modelled using linear and non-linear approaches. The results showed a pathogen-dependent response to the combined antimicrobial hurdles of the process. Salmonella Typhimurium was declined to levels below the detection limit by day 28 (–7.10 log CFU/g), while E. coli O157:H7 showed a progressive reduction (–3.61 log CFU/g) but persisted at detectable levels. L. monocytogenes exhibited the highest resistance, with only a limited reduction (–1.32 log CFU/g); however, no net growth was observed throughout the ripening period, indicating that the product environment did not support its growth. The ripening process was characterized by decreasing pH and water activity, driven by lactic acid bacteria growth, with no differences between inoculated and control samples. Non-linear models provided the best fit to the survival data, highlighting the presence of resistant subpopulations. Overall, the results suggest that ‘Nduja ripening creates conditions unfavorable for sustained pathogen proliferation, although the extent of microbial reduction differed among the investigated microorganisms. These findings provide useful data for the microbiological characterization of this traditional product and may support future risk assessment and process validation studies.

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