A routine validation with unexpected results
When our lab in Hebden Bridge updated their polymerase chain reaction (PCR) method for mollusc detection in 2024, the team expected a routine validation process. But what started as a technical check quickly turned into a scientific detective story. One that led from a scampi label to an unexpected discovery in everyday wheat flour. The culprit? Not faulty equipment, but traces of slugs and snails hiding in plain sight.
Why PCR methods need careful validation
As part of routine method improvement, our team at Hebden Bridge began revalidating its mollusc detection method using PCR. Although the method had been used for years, updates to the kit required full revalidation to ensure its reliability across the diverse food samples we receive.
For a contract laboratory, validations are rarely simple. Different sample types can behave unpredictably with allergen detection kits. ELISA methods, for example, often show poor recovery in complex matrices, triggering lengthy troubleshooting with kit suppliers and sometimes forcing a change of method altogether.
A scampi sample raises eyebrows
This time, the PCR validation was progressing smoothly, until the team reached the scampi sample. The result came back positive for mollusc. At first glance, this seemed expected: the product's label carried precautionary allergen labelling (PAL) for mollusc. But the team decided to investigate further.
To verify the result, they tested the scampi’s core ingredients – breadcrumbs and langoustines – separately. The langoustines tested negative for mollusc, while the breadcrumbs tested positive. This raised an important question: could there be cross-reactivity in the breadcrumbs?
The wheat flour connection
The investigation continued with two more tests: standard wheat flour and a gluten-free flour alternative. The wheat flour came back positive for mollusc, but the free-from flour did not. All signs pointed toward something in the wheat matrix reacting with the PCR kit.
The team shared their findings with the kit manufacturer, who had not encountered this issue in their own validations. To confirm the result, samples were sent for sequencing. The verdict? The PCR kit had detected DNA from the Grey Field Slug and Land Snail.
Slugs, snails and allergen implications
While a bit unsettling for the average cake-lover, the discovery raised serious food safety and allergen risk questions. Is it possible that mollusc allergens could be present in common ingredients like wheat flour? And if so, how should the industry respond to better protect consumers with mollusc allergies?
As for our team at Hebden Bridge, the discovery highlights just how important rigorous validation is and how science can sometimes lead you to surprising places. From method development to mollusc mysteries, it's all in a day’s work when you need to be sure.
For further information on our testing services, please contact:
Dr. Emma Ridley
General Manager | Hebden Bridge
t: +44 (0) 151 350 6666
About SGS
SGS is the world’s leading Testing, Inspection and Certification company. We operate a network of over 2,500 laboratories and business facilities across 115 countries, supported by a team of 99,500 dedicated professionals. With over 145 years of service excellence, we combine the precision and accuracy that define Swiss companies to help organizations achieve the highest standards of quality, compliance and sustainability.
Our brand promise – when you need to be sure – underscores our commitment to trust, integrity and reliability, enabling businesses to thrive with confidence. We proudly deliver our expert services through the SGS name and trusted specialized brands, including Brightsight, Bluesign, Maine Pointe and Nutrasource.
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