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

Abstract

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).

Effect of production process and high-pressure processing on viability of <em>Listeria innocua</em> in traditional Italian dry-cured coppa

“…Various authors have tested the inactivation of L. monocytogenes in other unfermented meat products by HPP (Garriga et al, 2004;Hugas et al, 2002;Merialdi et al, 2015), many of them in dry-cured ham (Morales et al, 2006;Bover-Cid et al, 2011;Hereu et al, 2012;Bover-Cid et al, 2015): Hereu et al (2012) have reported a reduction of L. monocytogenes from 1.82 to 3.85 log CFU/g in artificially contaminated sliced ham after treatment at 600 MPa for 5 min, Bover-Cid et al (2011), through a HPP treatment at 613 MPa for 5 min., achieved the 2.39D proposed by Hoz et al (2008) to meet the USA zero tolerance policy, Bover-Cid et al (2015) showed a reduction of L. monocytogenes in dry-cured ham at 600MPa for 5 minutes ranging from 2.24 log to 6.82 Log CFU/g depending on the a w and fat content of the ham.…”

“…The L. innocua inoculum culture was prepared using a mixture of 5 strains: IZSLER 111373/1 and IZSLER 111373/2 isolated from industrial site (superficial swab collected in pork meat transformation plant), IZSLER 257529/1 isolated from fresh pork sausages, IZSLER 257529/2 isolates from fresh swine meat and the reference strain ATCC 33090, 100 µL of a stock culture (stored in 20% glycerol at -80°C) of each strain were transferred to 10 ml Brain Heart Infusion (BHI) broth and incubated for 24 h at 30°C. Subsequently, an aliquot of 100 µl was transferred to 1000 mL BHI broth and incubated at 12°C for 72 h (Merialdi et al, 2015).…”

“…Over the 2016-2018 period, samples from pig meat were by far the main matrix tested for L. monocytogenes in the EU, 59.9% in 2018, out of the 24,814 RTE pig meat products tested, 1.3% was positive for L. monocytogenes, 1.4% at production level and 0.8% at retail level (EFSA and ECDC, 2019). Several authors evaluated the presence of L. monocytogenes in RTE pig meat products such as dry-cured ham (Garriga et al, 2004;Merialdi et al, 2015), dry-cured pork loins (Morales-Partera et al, 2017) and others dry-cured pig meat products including coppa, bacon and smoked speck (Meloni et al, 2009).…”