Survival of Listeria monocytogenes on sliced cooked sausage after treatment with pediocin AcH

A preparation with pediocin AcH bound to its heat-killed producer cells Lactobacillus plantarum WHE 92 (starter culture ALC01, Wisby, Denmark) by adjusting the pH of the preparation to 6.0 was studied for its effects against Listeria monocytogenes ATCC 7644 and (spoilage) lactic acid bacteria on sliced cooked sausage. The pediocin AcH preparation or 0.9% (w/w) NaCl dilution (as a control) were randomly distributed dropwise on the surface of the slices. Treated slices were vacuum-packed and stored at 6 °C. Microbiological analysis and determination of pH values were performed after 3, 6, 9, 14 and 21 days of storage. Flavour of the sausages was evaluated after 7 and 11 days of storage. The pediocin preparation had effect (p>0.05) neither on the growth of lactic acid bacteria, on the pH value nor on the flavour of vacuum-packed sliced sausage during 21 days of storage compared to control. However, during 6 days of storage, the number of L. monocytogenes decreased from the initial level of 2.7 log cfu/g sausage to <2 log cfu/g, while on the control sausages the number of L. monocytogenes remained at the inoculated level. The numbers of L. monocytogenes remained at those levels to the end of storage period (21 days). However, the treated samples were determined to be Listeria positive, which indicates that the pediocin preparation was not efficient enough to kill all L. monocytogenes.