Listeria monocytogenes in ready-to-eat foods

In its January circular, the Federal Agency for the Safety of the Food Chain, or FASFC for short, calls special attention to Listeria monocytogenes and more specifically in ready-to-eat foods. This includes all foods that can be consumed directly by the consumer, also known as ready-to-eat products. Regulation (EC) No. 2073/2005 names the microbiological criteria for foods including Listeria monocytogenes . Since these pathogenic bacteria can have serious consequences for public health, strict requirements apply. This article gives you a brief overview of what this circular means.

Criteria for Listeria monocytogenes.

For Listeria monocytogenes, two criteria are established for ready-to-eat foods, with the exception of infant formulae and foods for medical use. On the one hand, there is the criterion that assumes absence in 25 grams of product upon leaving the food establishment. This applies to ready-to-eat foods in which Listeria monocytogenes can grow (category 1.2). On the other hand, there is a limit of 100 KVE/g for ready-to-eat foods in which Listeria monocytogenes can survive but not grow. This limit applies for the duration of the shelf life of the product (category 1.3).

This automatically includes products with:

• pH ≤ 4.4;
• _aw ≤ 0.92;
• pH ≤ 5.0 and_aw ≤ 0.94;
• A shelf life of less than 5 days.

Shelf life

Food companies of products that are breeding grounds for Listeria monocytogenes should conduct studies to verify compliance with microbiological criteria during the shelf life. The shelf life can be substantiated in several ways. These are through:

1. Similar product features

It is important to have knowledge about the properties of manufactured foods, this especially about survival and growth potential of Listeria monocytogenes. These product properties should be consistent. In case of inconsistencies, always assume the worst case situation where the survival or growth of Listeria monocytogenes is most supported.

• Scientific literature

The substantiation from scientific literature should be described in detail in the autocontrol system if used to explain the behavior of Listeria monocytogenes . All relevant elements should be compared in detail with those of the ready-to-eat food. Moreover, all scientific references should be mentioned and made available during inspections and audits. Finally, the conclusions should be validated with a laboratory study.

• Historical data

Historical data is part of the food company's documentation. With no or few nonconforming results, confidence in the food safety system is strengthened. Analytical results on uncontaminated lots cannot be used to determine whether or not growth of Listeria monocytogenes is possible. However, these results can be viewed as verification tools for testing proper functioning of the food safety system.

• Predictive microbiology

Predictive microbiological models should be used with caution, especially by trained and experienced individuals. Moreover, any variability and worst case situation must be taken into account. Finally, the outcome should always be validated with laboratory studies using representative parameters.

• Laboratory Studies

Laboratory studies are used to determine the growth potential and maximum growth rate of Listeria monocytogenesin food during the predetermined shelf life. These are provocation tests, shelf-life tests or the combination of both.

1. Provocation testing (challenge testing).

For performing provocation tests, the European Union Reference Laboratory for Listeria monocytogenes has prepared a technical guideline. This informs the laboratory about temperature and time profiles at various stages of storage, distribution and use. Three different lots are tested. The results obtained can only be extrapolated when classified in the same category. Moreover, the FASFC only accepts these tests performed by accredited laboratories.

• Shelf life tests

Another option is a shelf-life test. This involves testing three contaminated lots as soon as possible after the determination of contamination. Per contaminated lot, shelf-life tests are performed on at least thirty samples. In addition, several products can be categorized as part of the self-checking system. The test is then performed with the worst case food product representative of that category.

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