BioProject

The bacteriocin Nisin, produced naturally by various Lactococcus lactis strains, is commonly used in the cheese industry as it displays broad-spectrum activity against many Gram-positive bacteria including Listeria monocytogenes. More...

The bacteriocin Nisin, produced naturally by various Lactococcus lactis strains, is commonly used in the cheese industry as it displays broad-spectrum activity against many Gram-positive bacteria including Listeria monocytogenes. In the ready-to-eat food sector L. monocytogenes poses a risk to minimally processed foods due to its ability to grow under refrigeration conditions. Many natural antilisterial products render Iceberg lettuce unsuitable for consumption within 2 days of storage and thus this study investigated the efficacy of Nisin as antilisterial agent and its sensory impact on lettuce. In-vitro assays confirmed the efficacy of Nisin to inhibit growth of a three strain mix of L. monocytogenes. Subsequently, this L. monocytogenes strain mix was added to lettuce that was treated either with Nisin, L. lactis DSM20729 or was kept treatment-free. Incubation took place at 4 and 8°C under various atmospheres. On days 0, 2, 5 and 7, Listeria was extracted from the food surface and enumerated on selective agar and a sensory panel graded the lettuce on product appearance. At 4 and 8°C a 10-100 fold reduction of Listeria growth was achieved with 5 ppm Nisin over a seven day period, while lettuce kept an acceptable sensory appearance over the first 5 days. Direct application of Nisin producing L. lactis had no detectable effect on Listeria growth in vitro and in situ. The bacterial community structure changed substantially over the 7 days of incubation with the genus Pseudomonas being most abundant and increasing to around 90% of relative abundance by day 7. Less...