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New method of tackling listeria in ready-to-eat foods

By Jane Byrne , 09-Sep-2008
Last updated on 09-Sep-2008 at 17:49 GMT

A new study has found the combination of natural antimicrobials with in-package pasteurization of ready-to-eat (RTE) turkey bologna is effective in reducing the L. monocytogenes pathogen and preventing outgrowth during refrigerated storage.

The findings of the Clemson University researchers were published in the journal, Food Microbiology.

The researchers claim that combining in-package pasteurisation with natural antimicrobial treatments is a novel approach to food preservation and has a greater impact on bacterial populations compared to interventions using a single treatment, reducing the need for intense heat treatment.

“Results from this study could have a significant impact for the industry since a reduction in bacterial contamination was achieved by a relatively short pasteurization time and antimicrobials reduced populations further during refrigerated storage,” said the research team.

Infection

L. monocytogenes is a pathogenic bacterium causing listeriosis, which is a rare but potentially lethal infection that can kill vulnerable people, such as the elderly and pregnant women, as well as those suffering from immuno-compromising diseases like cancer or HIV.

According to the US Centre for Disease Control and Prevention (CDC), 2,500 people are estimated to be seriously ill with listeriosis each year with about 500 of that total dying.

The International Life Science Institute states that foods considered as high-risk sources of listeriosis include products that are ready-to-eat, require refrigeration and are stored for extended time periods.

According to the study, L. monocytogenes can contaminate ready-to-eat meat and poultry during post-processing steps such as slicing, peeling and packaging.

Goals

The group said the objective of the project was to evaluate the efficacy of surface application of nisin, a natural antimicrobial with Generally Recognized As Safe (GRAS) FDA approval and/or lysozyme, derived from hen egg white. The substances were tested in combination with in-package pasteurization of RTE low fat turkey bologna against L. monocytogenes.

“Application of additional hurdles to control the growth of this organism would provide an increased margin of safety during refrigerated storage,” claim the researchers.

Method

RTE low fat turkey bologna averaging 14.3 per cent fat, 10.7 per cent protein, and 71.4 per cent moisture with 2 per cent salt was used for the experiment, according to the study.

The sterile bologna samples were treated with solutions of nisin, lysozyme, and a mixture of the two antimicrobials before in-package pasteurization at 65°C, claim the researchers.

Results

The researchers said the in-package pasteurization resulted in an immediate 3.5 to 4.2 log reduction in L. monocytogenes for all treatments and that all pasteurized treatments also resulted in significant reduction of the pathogen by 12 weeks compared to un-pasteurized bologna.

In-package pasteurization allied with nisin-lysozyme treatments was effective in reducing the bacterial population by below detectable levels by two-three weeks of storage.

The researchers claim that the intervention methods used in the study satisfy the requirements of alternative 1 of the interim final rule of the United States Department of Agriculture (USDA) in regard to its regulation aimed at controlling L. monocytogenes in plants that produce RTE meat and poultry.

Alternative 1 requires the use of a post-lethality treatment to reduce the initial bacterium and an antimicrobial agent to suppress or limit the growth of the pathogen during storage.

The researchers claim their method employs low levels of both treatments:

“This fact would help the industry in developing a cost-effective pasteurization method to control L. monocytogenes in RTE meat products and to preserve the desirable qualities of the food product,” added the research team.

Source: Food Microbiology
"Effect of combining nisin and/or lysozyme with in-package pasteurization for control of Listeria monocytogenes in ready-to-eat turkey bologna during refrigerated storage"
Published online ahead of print
Authors: S. Mangalassary, I. Han, J.Rieck, J. Acton, P. Dawson

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