Ocratossina A e Listeria monocytogenes in prosciutti crudi San Daniele: presenza, prevenzione ed eliminazione

Ochratoxin A and L. monocytogenes in San Daniele dry cured ham: occurrence, reduction and prevention. The fungal population of the plants and of dry cured ham of San Daniele is varied and complex. However, it does not seem to be formed from species producing ochratoxin A (OTA), in contrast to that observed by other authors. Nevertheless we wanted to evaluate "in vitro" for the production of OTA in all species of Aspergillus and Penicillium, isolated from ripening rooms and dry cured ham. None has shown the ability to synthesize OTA. Consequently, based on what is observed it can exclude the presence of this mycotoxin on surfaces or in the meat of San Daniele ham. Furthermore, the use of a starter consisting in Penicillium nalgiovense, Candida guilliermondii or Saccharomycopsis fibuliger, prevents the development of micotossigenic mold in ham during the pre-curing and aging. The antilisterial activity of generally recognized as safe (GRAS) bacteriophage Listex P100 (phage P100) is demonstrated in broths and on the surface of slice of dry cured ham and pork skin against 19 strains or serotypes (i.e. 2a, 1/2a, 4b) of Listeria monocytogenes. In a broth model system, phage P100 completely inhibited either 2 log CFU/cm2 or 3 log CFU/cm2 of L. monocytogenes growth at 30 °C at phage concentrations equal or upper than 7 log PFU/ml. The temperature (4, 10, 20 °C) seemed not to influence the phages activity, nevertheless at 4 °C it was possible obtained the best results. On dry cured ham slices, a phage concentration from 5 to 8 log PFU/cm2 was required to obtain significant L. monocytogenres reduction. In particular at 4 °C an inocolum of 8 PFU was required to eliminate completely a concentration of 2 log L. monocytogenes/cm2 and to reach 0 tolerance according USA food law. At 10 and 20 °C the reductions were less significatives and yielded 3.0 and 2.4 log CFU/cm2 . Phage P100 remained stable on dry cured ham slices over a 14 day storage period, with only a marginal loss of 0.2 log PFU/cm2 from an initial phage treatment of 8 log PFU/cm2. Moreover phage P100 allowed to eliminate free L. monocytogenes cells and its biofilms on the surfaces of the rooms of dry cured ham plant production. These findings illustrate that the GRAS bacteriophage Listex P100 is listericidal on dry cured ham and is useful in quantitatively reducing L. monocytogenes.