Growth of Listeria monocytogenes on shredded, ready-to-eat iceberg lettuce

Listeria monocytogenes, when present, could be able to grow on Ready-to-Eat (RTE) iceberg lettuce. This investigation demonstrates that L. monocytogenes grows on packaged shredded iceberg lettuce held at 13 or 5 °C (maximum growth rate of 0.019 and 0.013 log cfu/h, respectively), with increments of 4.85 and 2.66 log cfu/g, respectively, after 14 days. No lag time was observed at 13 °C, in contrast with that at 5 °C (5.6 days). Initial atmosphere inside the packages was 4.65–6.2% CO2, 2.1–4.3% O2 and a balance of N2. Five predictive models taken from literature gave conservative predictions at 13 °C, although at 5 °C they were closer. Lactic acid and psychrotrophic bacteria showed similar growth at both temperatures. In general, the MAP system reported here retarded the growth of L. monocytogenes in comparison with other works without initial flushing of gases.