CASE STUDY: The murky waters of the tuna controversy
Subway, one of the world’s largest sandwich chains, has been questioned about the authenticity of their tuna. Seafood fraud – particularly the mislabelling and substitution of fish species – is a global concern.
There have been many learnings, as the story has unfolded. Recent news reports have again highlighted the importance of making sure that the right questions are asked, appropriate actions are taken and correct interpretations are made, to enable a thorough assessment of all the relevant details.
BACKGROUND: Timeline of events
THE NEW YORK TIMES INVESTIGATION
- INTRODUCTION
The New York Times started their pilot study with a search for a commercial laboratory that could test a sample of the Subway product. A few laboratories declined the request, on account of technical limitations or company policies that made the tuna ineligible for testing.
The laboratory that agreed to perform the analysis also voiced hesitations regarding testing and highlighted the challenges of the sample matrix.
- METHOD
Sandwich samples from three different locations were obtained. Effort was put in to ensure that the sandwiches consisted of tuna filling only, and did not also include vegetables, cheese or dressing. The samples were packaged in Ziploc bags, placed in an styrofoam shipping cooler with a few ice packs, and mailed across the country. The first shipment was lost in transit, and the exercise was repeated. When they were finally received by the testing laboratory, a PCR test was conducted on the samples.
- RESULTS
The results released stated that “no amplifiable tuna DNA was present in the sample, and so we obtained no amplification products from the DNA. Therefore, we cannot identify the species.” The laboratory staff stated further that there were two possible reasons for this: either the sample was too heavily processed to successfully identify the species, or there was no tuna present.
DISCUSSION OF THE INVESTIGATION: What does this all mean?
For a variety of reasons, the outcome of the testing may seem alarming to some. However, once again the results only indicate the importance of truly understanding test-method capabilities and result interpretation.
There is a broad mix of testing techniques currently in use for species identification, including both protein-based and DNA-based methods. Polymerase chain reaction (PCR) is a DNA-based method that is widely used for species identification.
A variety of PCR applications are available for fish species identification. These applications are all based on polymorphisms in the genetic codes of different species. Two methods that are used in industry are PCR-RFLP and FINS.
However, certainty of identification of an organism through the use of DNA-based testing is dependent on a number of factors. It has been noted that PCR-RFLP may give incorrect identifications, especially with tuna species. Sequencing-based approaches are more definitive, but these methods rely on the length and quality of the DNA sequence, as well as on a high-quality reference database for sequence identification. In addition to this, samples that contain multiple species cannot easily be analysed.
Testing viability is also primarily reliant on factors related to the quality of the DNA present in a sample. Processing steps, such as cooking or hydrolysis, can degrade and destroy the DNA in a sample, to the point that it is no longer viable to detect it with PCR. Additionally, a number of compounds present in processed foods may also serve as inhibitors of DNA amplification.
The tuna used in Subway’s products undergoes cooking and treatment steps during processing. Furthermore, it is often mixed with mayonnaise to form the filling on the sandwiches.
All of the factors mentioned above could contribute to false negative or inconclusive results. For this reason, it is of the essence that test results should not be viewed in isolation.
The discrepancy in the results, compared to these from the investigation by Inside Edition, may be due to factors related to the sample matrix, testing capabilities, methods used by the different laboratories, laboratory staff expertise and the sampling process (to name only a few).
Since proteins can be used as markers for many properties of a food, they can provide evidence to confirm the authenticity of food. Proteomic methods have shown success in identifying fish species-specific proteins. Protein-based methods are often performed at a peptide scale (as is the case with LC-MS/MS), making detection independent of the tertiary structure of the protein, highly specific, and still feasible after food processing (i.e. even if certain processing techniques cause the proteins to denature, they can still be identified). Therefore, protein-based methods are a solution to the limitations faced by DNA-based methods.
In addition to our range of DNA-based methods, the FACTS laboratory offers species identification through targeted proteomics by LC-MS/MS. Our extensive experience and expertise in species detection, including fish speciation, gives us the necessary insight to understand method capabilities, challenges and applications. Our unique ability to offer both DNA- and protein-based methods ensures we can offer appropriate and accurate species authenticity analyses; consequently, we can support industry with suitable approaches to detecting fraud and achieving their testing objectives.
When Subway was questioned on whether the findings may have been due to intentional mislabelling, they dismissed the possibility, indicating that if fraud were taking place, it would most probably be happening at the cannery. The director of the Ending Illegal Fishing Project at the Pew Charitable Trusts agreed that it would be difficult to place blame at Subway’s door if this were the case.
However, every role player in the food industry is liable and accountable for addressing the vulnerabilities in their own supply chains. Although Subway claims fraud is not taking place at their sites, it is their responsibility to ensure that their suppliers provide them with safe, authentic and good-quality food.
Furthermore, Subway has more than 40 000 outlets worldwide. What might be true in one location may not necessarily be the case at another.
Having a robust VACCP (Vulnerability Assessment and Critical Control Points) system and Supplier Assurance plan in place gives a company confidence in its supply chain, and will consequently give consumers confidence in their products.
PCR-restriction fragment-length polymorphism (PCR-RFLP)
A specific fragment of DNA is amplified by PCR, cut using restriction enzymes, and the fragments are separated by gel electrophoresis. Different species have different polymorphisms, which produce distinct banding patterns suitable for identification.
Forensically informative nucleotide sequencing (FINS)
A specific fragment of DNA is amplified by PCR, followed by DNA sequencing. The sequence is then compared to a large, authenticated database of fish species using matcher software, in order to allow accurate fish-species identification.
Liquid chromatography–mass spectrometry/mass spectrometry (LC-MS/MS)
A technique that combines the separating power of liquid chromatography with the highly sensitive and selective mass-analysis capability of triple-quadrupole mass spectrometry to detect fish species-specific peptides (i.e. proteins).
Recap on Fish and Seafood Fraud
Food fraud in the fishery sector is a recurring issue worldwide. Seafood is one of the most globally traded food commodities, and the supply chains are often quite complex; therefore, it tends to be highly vulnerable to substitution and mislabelling.
Recent studies and published records of food fraud incidents show a large number of fish and seafood products being mislabelled. In some cases, fish are labelled as different species from the same family. Other cases reveal species substitution with an endangered or vulnerable species. In addition to promoting unfair trade, misleading consumers and threatening efforts towards sustainability, a variety of public health risks have also been raised as a consequence.
Seafood products are not always deliberately mislabelled (i.e. it may occur due to negligence or technical incompetence). However, the vast majority of substitutions involve replacing higher-cost species with lower-cost species. This clearly indicates food fraud at play, rather than negligence.
CONCLUSION: The way forward
In situations with this many moving parts, it is often difficult to extract the truth. One cannot focus on only one piece of the puzzle. All the details should be considered before any conclusions are drawn.
Although the plaintiffs changed their allegations – which causes one to question how reliable the original claims were, that the product was ‘’anything but tuna’’ – uncertainty remains as to whether the more recent test results were due to the evident limitations of the method used.
This case should be investigated further before any assumptions are made regarding whether food fraud has taken place. While the story continues to unfold, here are some of the key learnings so far from this case study:
- All test methods have limitations. It is extremely important to understand testing capabilities, in order to conduct appropriate testing and interpret results accurately.
- Testing is not a standalone solution; often, a multi-tiered approach is required to determine product authenticity.
- In a world filled with food fraud, addressing the vulnerabilities throughout your supply chain is of the essence, to protect your brand and to ensure consumer assurance. Demonstrating due diligence and implementation of food-fraud prevention is fundamental.
- Regardless of the legal outcome of cases such as this one, reputation and brand damage may be (and often are) unavoidable. It is useful to follow a testing schedule which allows for a history of product authenticity testing and trends, as support in situations when they may be required to defend against claims of food fraud.
THE BOTTOM LINE:
Determining tuna authenticity in this case may have seemed like shooting fish in a barrel, but has once again demonstrated that DNA-based testing is not always a silver bullet!
Species-identification testing plays a vital role in detecting, deterring and preventing food fraud. However, choosing a suitable test method is key to ensuring valid results for accurate interpretation, and consequently, appropriate action. Protein-based methods for species detection can be the solution to the challenges experienced when using DNA-based methods.
The FACTS laboratory offers Industry-leading species identification, including seafood and fish speciation.
Our dynamic team of experts understand the importance of choosing an appropriate approach to achieve your testing objectives.
Contact us for more information on the range of species-identification, authenticity-testing and food fraud-prevention services we offer.