Reduction of Listeria innocua contamination in vacuum-packaged dry-cured Italian pork products after high hydrostatic pressure treatment

The present work aims to present the results of the application of a treatment with high hydrostatic pressure (HHP) on Italian fermented and dry-cured pork products. The products used in this study were portioned cured ham, portioned bacon and salami, vacuumpackaged and produced by a single processing company. Two studies were conducted on a single batch of the three products by means of an artificial contamination with Listeria innocua as a surrogate of L. monocytogenes. In the first trial a superficial contamination was obtained by immersion for 3 min in the culture broth with a concentration of approximately 9 log cfu/mL. At the end of the inoculum step, the pieces were dred at room temperature and vacuum packaged. In the second trial 50 kg of minced pork meat were contaminated before production of salami. In both cases the inoculum contained 5 strains of L. innocua. Subsequently, in both trials, 10 samples were randomly divided into two groups of 5 pieces each: i) TH group, samples treated with HHP; ii) group C, control samples, not subjected to any treatment. All samples were stored at refrigeration temperature at the end of HHP treatments (if applied), and analyzed for the determination of the surface (1st trial) and deep (2nd trial) quantitative contamination of L. innocua. pH and aW were also determined on 3 pieces of each products belonging to group C. The difference between the medians of the log cfu/cm² or g established between controls and treated were compared using the non-parametric test (Kruskal-Wallis test) with P<0.01. In all products and in both trials the level of contamination detected in treatment groups was always significantly lower than in controls (P<0.01). In particular, in vacuum-packaged ham, bacon and salami viability logarithmic viability reductions equal to -2.29, -2.54 and -2.51 were observed, respectively. This study aimed to evaluate a not-thermal treatment on Italian cured or fermented pork products. The results of this study need to be confirmed in different products and in a greater number of lots, but they appear promising, also because of the considerable literature available for different categories of products (cheese, vegetables and fruit).