Sensitivity to Pulsed Light Technology of Several Spoilage and Pathogenic Bacteria Isolated from Fish Products

The effect of pulsed light (PL) on the inactivation of six fish spoilage bacteria (Photobacterium phosphoreum, Serratia liquefaciens, Shewanella putrefaciens, Brochothrix thermosphacta, Pseudomonas group I, and Pseudomonas groups III and IV), six Listeria monocytogenes isolates from fish products, and one strain of Listeria innocua was evaluated. For all tested strains, grown at 4 degrees C (temperature to process, store, and distribute convenient, lightly preserved fish products), the maximum detectable inactivation (6 to 6.5 log) was observed after treatments lower than 0.3 J/cm(2). The most sensitive bacteria were P. phosphoreum and S. liquefaciens, while both L. innocua and L. monocytogenes were the most resistant species to PL. Bacterial inactivation kinetics depended on their susceptibility to PL. Typically, sigmoidal curves were observed, with an initial shoulder followed by an exponential loss of cell culturability down to the maximum detectable inactivation. However, no initial shoulder was pointed out for the most sensitive species (P. phosphoreum and S. liquefaciens). Since the PL resistance of all tested Listeria strains (L. innocua and L. monocytogenes isolates) was similar, we propose the use of L. innocua as a surrogate for L. monocytogenes in PL technology validation.