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United States Department of Agriculture

Agricultural Research Service

Research Project: MICROBIAL MODELING AND BIOINFORMATICS FOR FOOD SAFETY AND SECURITY Title: Modeling the Growth Characteristics of Listeria Monocytogenes and Native Microflora in Smoked Salmon

item Hwang, Cheng-An
item Sheen, Shiowshuh

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 3, 2008
Publication Date: April 1, 2009

Interpretive Summary: Contamination of processed smoked salmon with Listeria monocytogenes has been reported. Understanding the growth ability of this pathogen in smoked salmon during storage allows control measures to be developed to reduce the risk of foodborne illness caused by this deadly pathogen. This study was conducted to determine and model the growth ability of L. monocytogenes and native microorganisms in smoked salmon at refrigerated (4 degree C) and abuse temperature (8, 12, 16 degree C) conditions. Results showed that L. monocytogenes and native microorganisms were able to grow in smoked salmon at all storage temperatures, and L. monocytogenes grew at a similar rate as native microorganisms. Mathematical models were developed to predict the growth characteristics of L. monocytogenes and native microorganisms and the growth relationship between these two microflora in smoked salmon. These models will be used by the processors to predict the growth potential of L. monocytogenes in their products and develop processing and handling control measures to reduce the contamination and growth of L. monocytogenes.

Technical Abstract: Smoked salmon contaminated with L. 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 log10 2.9 cfu/g was inoculated with a 6-strain mixture of L. monocytogenes to levels of log10 1.6 (low inoculum) and log10 2.8 (high inoculum) cfu/g, and stored at 4, 8, 12, and 16 degree C. Growth characteristics (lag phase duration [LPD, h], growth rate [GR, log10 cfu/h], and maximum population density [MPD, log10 cfu/g]) of L. monocytogenes and native microflora were determined. At 4-16 degree C, the LPD, GR, and MPD were 254 to 35 h, 0.0109 to 0.0538 log10 cfu/h, and 4.9 to 6.9 log10 cfu/g for L. monocytogenes, respectively, and were 257 to 29 h, 0.0102 to 0.0565 log10 cfu/h, and 8.5 to 8.8 log10 cfu/g for native microflora. The growth characteristics of L. monocytogenes or the background 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.

Last Modified: 4/18/2015
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