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Model growth characteristics of Listeria monocytogenes and native microflora in smoked salmon.

Smoked salmon contaminated with Listeria monocytogenes has been implicated in a number of outbreaks of foodborne listeriosis over the years. The bacteria's ability to grow at temperatures as low as 0 C enables it to multiply in refrigerated products.

UADA-ARS scientists set out to examine the growth characteristics of L. monocytogenes and native microflora in smoked salmon stored at refrigerated and abuse temperatures. As part of their research, the investigators developed models that can be used to estimate the growth characteristics of L. monocytogenes and native microflora in smoked salmon. You might use the models to assess the microbiological safety and quality of the product during storage at refrigerated and abuse temperatures.

Smoked salmon samples with a native microflora count of 2.9 [log.sub.10] cfu per gram were inoculated with a six-strain mixture of L. monocytogenes to levels of 1.6 [log.sub.10] and 2.8 [log.sub.10] cfu per gram. The samples were vacuum-packed and stored at 4 C, 8 C, 12 C and 16 C.

The researchers determined various growth characteristics, including the lag phase duration, growth rate and maximum population density of the bacteria and native microflora. At 4 C to 16 C, the duration of the lag phase, growth rate and maximum population density ranged from 254 hours to 35 hours, from 0.0109 to 0.0538 [log.sub.10] cfu per hour, and 4.9 to 6.9 [log.sub.10] cfu per gram for L. monocytogenes, respectively. At 4 C to 16 C, the duration of the lag phase, growth rate and maximum population density ranged from 257 to 29 hours, from 0.0102 to 0.0565 [log.sub.10] cfu per hour, and from 8.5 to 8.8 [log.sub.10] cfu per gram for native microflora, respectively.

The initial levels of L. monocytogenes didn't significantly affect the growth characteristics of L. monocytogenes or the native microflora in smoked salmon. The scientists' predictive models described the lag phase duration, growth rate and maximum population density of L. monocytogenes and native microflora as a function of storage temperature.

The growth relationship between L. monocytogenes and native microflora, which also was modeled, showed that the duration of the lag phase and the growth rate of L. monocytogenes were similar to those of the native microflora.

Further information. Cheng-An "Andy" Hwang, USDA-ARS Eastern Regional Research Center, Room 2125.2, 600 E. Mermaid Lane, Wyndmoor, PA 19038; phone: 215-233-6416; fax: 215-233-6581; email: andy.hwang@ars.usda.gov.
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Publication:Emerging Food R&D Report
Date:Mar 1, 2013
Words:415
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