Modeling the growth characteristics of Listeria monocytogenes and native microflora in smoked salmon

Smoked salmon contaminated with Listeria monocytogenes has been implicated in foodborne listeriosis. The objectives of this study were to model the growth characteristics and examine the growth relationship of L. monocytogenes and native microflora in smoked salmon. Smoked salmon samples with a native microflora count of 2.9 log(10) CFU/g were inoculated with a 6-strain mixture of L. monocytogenes to levels of log(10) 1.6 and log(10) 2.8 CFU/g, and stored at 4, 8, 12, and 16 degrees C. Growth characteristics (lag phase duration [LPD, h], growth rate [GR, log(10) CFU/h], and maximum population density [MPD, log(10) CFU/g]) of L. monocytogenes and native microflora were determined. At 4 to 16 degrees C, the LPD, GR, and MPD were 254 to 35 h, 0.0109 to 0.0538 log(10) CFU/h, and 4.9 to 6.9 log(10) CFU/g for L. monocytogenes, respectively, and were 257 to 29 h, 0.0102 to 0.0565 log(10) CFU/h, and 8.5 to 8.8 log(10) CFU/g for native microflora. The growth characteristics of L. monocytogenes or the native microflora were not significantly different (P > 0.05), regardless the initial levels of L. monocytogenes. Mathematical equations were developed to describe the LPD, GR, and MPD of L. monocytogenes and native microflora as a function of storage temperature. The growth relationship between L. monocytogenes and native microflora was modeled and showed that the LPD and GR of L. monocytogenes were similar to those of native microflora. These models can be used to estimate the growth characteristics of L. monocytogenes in smoked salmon, and thereby enhance the microbiological safety of the product.