Beware of solution by dilution: The risk of compositing samples
Compositing – the practice of combining multiple subsamples to create a single sample – is widely used in food testing to provide a more comprehensive view of, for example, a batch of product. While compositing is a useful tool, it can present unique challenges and risks when applied to allergen testing.
The crux of the issue lies in the nature of allergen cross-contact. If the allergen cross-contact is homogenous and evenly dispersed throughout a product, compositing may yield a meaningful result – but this is seldom the case. Allergen cross-contact, in most instances, is heterogeneous, sporadic and present at varying concentrations, making compositing a risky strategy.
Risks of compositing for allergen testing
Diluting cross-contact allergens
When compositing, if only one subsample contains allergen cross-contact and it’s mixed with other subsamples that are free from the cross-contact allergen, the allergen may be diluted below the test’s reporting limit, or to a level that does not point to a significant risk to consumers.
- If, by compositing, the allergen cross-contact is diluted to below the test’s reporting limit, it can lead to a false negative result. This would give the impression that all subsamples were free from the allergen, when this is not true.
- If, by compositing, the allergen cross-contact is diluted to below a level that is a significant risk to consumers, it can lead to a false sense of security. This would give the impression that the product as a whole contains cross-contact at levels below what is considered a risk.
In both scenarios, the results of the composite sample are not a true reflection of risk and therefore, do not provide meaningful information.
Additionally, this ‘solution by dilution’ is even more problematic when compositing across different product variations, for example, products with different ingredients or formulations.
When allergen cross-contact is sporadic or involves particulates, allergen detection becomes a matter of chance — the more individual samples you test, the better your chances of detection. It’s like searching for a needle in a haystack. Compositing those samples reduces your odds even further, making it more likely that the allergen will go undetected and the cross-contact risk will be misinterpreted.
Loss of traceability
Another challenge with compositing samples for allergen testing is the loss of traceability. If allergens are detected in a composite sample, you will not be able to pinpoint the source of cross-contact without retesting all the subsamples to determine which one(s) contained allergens. This makes root cause investigation and corrective action more difficult, and delays response.
Non-compliance with regulatory requirements
When testing final products to support ‘free from’ allergen claims, the Regulations Relating to the Labelling and Advertising of Foodstuffs (R. 146/2010, as amended) require that the foodstuff on which the claim is made must be tested to confirm the absence of the relevant allergen(s), using suitable testing for the specific allergen(s).
This implies that the final product itself must be tested – not a composite of multiple variations. Compositing different product variants (e.g. several flavours of chocolate bar, all bearing a ‘gluten-free’ claim) does not align with R. 146 requirements.
Practical example: Validating allergen cleaning using next-product testing
When validating cleaning after an allergen-containing production run, it might seem like a good idea to test a composite sample made up of product taken from the start, middle and end of the next product run, to prove the production line is clean.
However, this approach can dilute allergen cross-contact — particularly from the start of the production run which is likely to have the highest risk of allergen carryover from the previous allergen-containing production run.
Consequently, a composite sample may return a false low-level or false negative result, failing to detect the allergen cross-contact that could still pose a risk to allergic consumers.
Best practice:
Test the first product manufactured separately to accurately assess potential allergen carryover. Only include individual samples from the middle and end of the run if results from the first sample show significant allergen presence. Testing samples from the middle and end of the run will help track the decline, and pinpoint when cross-contact becomes negligible.
When can compositing be justified for allergen testing?
There are some instances in which compositing can be justified for allergen testing; but this largely depends on the nature of the potential allergen cross-contact, the product and process, the testing objective and the sampling strategy rationale.
Our allergen management consultants can help review these factors, and advise you on the best approach; so get in touch with us for practical, science-based support that aligns with real-world risk.
If you are compositing samples for allergen testing, here are some basic tips to keep in mind:
- Very importantly, ensure the test sensitivity is adequate for the risk.
- Keep original samples so that in the case of a positive result, you can test them individually.
- Record why and how compositing is being done as part of your allergen control plan.
Takeaway message
Compositing is often used with good intentions: to cut costs, improve efficiency, or create more representative samples. However, in allergen testing – where even trace cross-contact matters – this approach can undermine the very goal of detecting risk.
As with all food testing, results only reflect the sample tested. A one-size-fits-all sampling plan does not exist, so speak to our team if you have any doubts when developing or reviewing your sampling strategy. Do not let a clean composite result give you a false sense of security.
Other articles and resources you may be interested in:
The building blocks of a recall-proof allergen control plan
Meaningful allergen quantitative risk assessment