In Summary
- Detection of Listeria in food or processing environments should be investigated, with follow up remedial action taken. Including the review of HACCP and pre-requisites.
- Single results are important, however it is recommended that results be collated to provide reliable historical data. This can be used to look for changes over time.
- To provide evidence that the levels of L. monocytogenes remain below 100 cfu/g throughout shelf life of a product, shelf-life studies should be carried out, these are explained more below.
- Smaller businesses may choose to work with their local authority’s environmental health officers to find appropriate strategies to ensuring compliance.
Any detection of Listeria species in the food or environment should be investigated and follow-up remedial action carried out and documented, reviewing HACCP and prerequisites, and re-establishing its efficacy.
Food safety is dependent on functioning HACCP. You can read guidance on developing a HACCP on the FSA website.
Data gathering supports HACCP and is an ongoing process. Adverse results must be investigated and actioned to ensure continuing improvement. The data collected should be sufficient to provide confidence in the safety of the product.
It is not possible to indicate precisely how much historical day of production and end of life data is needed to set shelf life but the level of confidence in the shelf life being appropriate increases with the size of the data set corroborating it, i. e. the more product units that have been tested the more reliable the historical data becomes. A product shelf life must be reduced if it cannot be demonstrated that the level of 100 cfu/g will not be compromised.
Food business operators should keep documentation as agreed with their EHO. Typical information might include shelf-life studies and any verification as a part of the GHP and HACCP procedures.
Although the format of the documentation can be decided by the FBO, shelf-life studies shall always include:
- specifications of physico-chemical characteristics of the product (such as pH, aw, salt content, concentration of preservatives and the type of packaging system) considering the processing steps and conditions, storage and the possibilities for contamination and the foreseen shelf-life.
- consultation of the available historic test results from the FBO’s durability testing program, scientific literature and research data regarding the survival and growth characteristics.
When the studies mentioned above are not able to give the necessary confidence in relation to the safety of the product, the FBO should conduct additional studies.
These additional studies should consider the inherent variability linked to the product and the processing and storage conditions. Such studies may include:
- predictive microbiological (mathematical) modelling established for the food in question, using critical survival or growth characteristics for the microorganisms of concern in the product.
and/or
- studies to evaluate the growth or survival of the micro-organisms of concern that may be present in the product during the shelf-life under reasonably foreseeable conditions of distribution, storage, and use (referred as durability
studies or adequate historical data), and/or
- tests to investigate the ability of the appropriately inoculated micro-organism of concern to grow or survive in the product under different reasonably foreseeable storage conditions (referred as challenge tests).
There is a 30-minute presentation available that explains the basics of shelf life determination for ready to eat foods, which can be found here (external link).
If the food manufacturer cannot provide scientific evidence to show how the shelf-life was determined, the simplest approach for many small businesses may be to negotiate with the competent authority for compliance to the stricter limit of absence of L. monocytogenes before the product leaves the point of manufacture.
Article 5 of the Microbiological Criteria Regulations (EC 2073/2005) states that set sampling plans must be followed, however the legislation allows businesses to adapt sampling plans so that they are proportionate to the size and type of business and food produced. This is only allowed where there is suitable historical evidence to be able to show that the food that is produced meets the limits stated in the Regulations. New businesses with no historical information would be required to comply with the five samples per batch required in the set sampling plans.
