The antilisterial effect of Leuconostoc carnosum 4010 and leucocins 4010 in the presence of sodium chloride and sodium nitrite examined in a structured gelatin system

To further enhance biopreservation of meat products, the antilisterial effect of the newly described protective culture Leuconostoc carnosum 4010 and its bacteriocins, leucocins 4010, was examined in the presence of sodium chloride and sodium nitrite in a solid matrix using a structured gelatin system. Interaction between Listeria monocytogenes 4140 and Leuc. carnosum 4010 or the leucocins 4010-resistant mutant L. monocytogenes 4140P showed that the inhibitory effect of Leuc. carnosum 4010 in the gelatin system was caused by the production and activity of leucocins 4010. The presence of sodium chloride (2.5% w/v) and sodium nitrite (60 mg/l) reduced the antilisterial effect of Leuc. carnosum 4010 in the structured gel system compared to the use of Leuc. carnosum 4010 alone. Investigations carried out at 10 degrees C showed that the lag phase of L. monocytogenes 4140 in the presence of Leuc. carnosum 4010 was reduced from 71 to 58 h by the addition of sodium chloride and to 40 h by the addition of sodium nitrite. Addition of sodium chloride increased the maximum specific growth rate of L. monocytogenes 4140 in the presence of Leuc. carnosum 4010 from 0.02 to 0.06 h(-1), whereas no change was observed by the addition of sodium nitrite. Compared to the antilisterial effect of leucocins 4010 alone, the addition of sodium chloride (2.5%, w/v) decreased the antilisterial effect at high concentrations of leucocins 4010 (5.3 and 10.6 AU/ml) as measured after 11 days of incubation at 10 degrees C. In gels with added leucocins 4010, the most pronounced reduction in growth of L. monocytogenes 4140 was observed at the highest concentration of leucocins 4010 (10.6 AU/ml) together with sodium nitrite (60 mg/l). More detailed information on the lag phase and the maximum specific growth rate of single colonies of L. monocytogenes 4140 in the presence of leucocins 4010 was obtained using microscopy and image analysis. No pronounced difference in the growth of single colonies was observed in the gel system. Real-time measurements of colony growth at 10 degrees C in the gelatin matrix showed that the growth inhibiting effect of leucocins 4010, including a longer lag phase as well as a lower maximum specific growth rate for L. monocytogenes 4010, was negated in the presence of 2.5% (w/v) sodium chloride.     

The survival and persistence in the human gastrointestinal tract of five potential probiotic lactobacilli consumed as freeze-dried cultures or as probiotic sausage

Among five lactobacilli (L. plantarum MF1291, MF1298, DC13, L. pentosus MF1300 and L. salivarius DC5) which were administrated as freeze-dried cultures for 17 volunteers, MF1298 and DC13 were the most frequently reisolated strains in faeces demonstrating the human gastric survival of these strains. Furthermore, MF1298 and DC13 persisted in the same volunteer after ended intake, suggesting host-specific persistence behaviour. When MF1298 was administrated as sausage fermented with this strain, the number of volunteers harbouring MF1298 increased from 4 to 10 indicating that the sausage matrix protects the survival through the gastrointestinal tract (GIT).