Authentication of swordfish (Xiphias gladius) by RT–PCR and FINS methodologies

The use of molecular markers in the verification of fish and seafood authenticity and the detection of adulteration

The verification of authenticity and detection of food mislabeling are elements that have been of high importance for centuries. During the last few decades there has been an increasing consumer demand for the verification of food identity and the implementation of stricter controls around these matters. Fish and seafood are among the most easily adulterated foodstuffs mainly due to the significant alterations of the species' morphological characteristics that occur during the different types of processing, which render the visual identification of the animals impossible. Even simple processes, such as filleting remove very important morphological elements and suffice to prevent the visual identification of species in marketed products. Novel techniques have therefore been developed that allow identification of species, the differentiation between species and also the differentiation of individuals that belong to the same species but grow in different populations and regions. Molecular markers have been used during the last few decades to fulfill this purpose and several improvements have been implemented rendering their use applicable to a commercial scale. The reliability, accuracy, reproducibility, and time-and cost-effectiveness of these techniques allowed them to be established as routine methods in the industry and research institutes. This review article aims at presenting the most important molecular markers used for the authentication of fish and seafood. The most important techniques are described, and the results of numerous studies are outlined and discussed, allowing interested parties to easily access and compare information about several techniques and fish/seafood species.

DNA-based techniques for seafood species authentication

Global trade of seafood has increased in the last decade, leading to significant concerns associated with seafood fraud. Seafood fraud involves the intentional misrepresentation of fish or shellfish for the purpose of economic gain and includes acts such as species substitution, illegal transshipment, overtreatment/short weighting, and mislabeling country of origin or production method. These fraudulent acts have had economic, environmental, and public health consequences on a global level. DNA-based techniques for seafood authentication are utilized by regulatory agencies and can be employed as part of a food fraud risk mitigation plan. This chapter will focus specifically on the use of DNA-based methods for the detection of seafood species substitution. Various methods have been developed for DNA-based species identification of seafood, including polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), species-specific PCR, real-time PCR, Sanger sequencing, microarrays, and high-resolution melting (HRM). Emerging techniques for seafood authentication include droplet digital PCR, isothermal amplification, PCR-enzyme-linked immunosorbent assay (ELISA), and high-throughput or next-generation sequencing. Some of these DNA-based methods target specific species, such as real-time PCR and droplet digital PCR, while other methods allow for simultaneous differentiation of a wide range of fish species, including Sanger sequencing and high-throughput sequencing. This chapter will begin with an introduction on seafood fraud and species substitution, followed by an analysis of the main DNA-based authentication methods and emerging techniques for species identification.

Swordfish or Shark Slice? A Rapid Response by COIBar-RFLP

Market transparency is in strong demand by consumers, and the authentication of species is an important step for seafood traceability. In this study, a simple molecular strategy, COIBar–RFLP (cytochrome oxidase I barcode–restriction fragment length polymorphism), is proposed to unveil commercial fraud based on the practice of species substitution in the swordfish trade. In particular, COI barcoding allowed the identification of the species Prionace glauca, Mustelus mustelus, and Oxynotus centrina in slices labeled as Xiphias gladius. Furthermore, the enzymatic digestion of COI amplicons using the MboI restriction endonuclease allowed the simultaneous discrimination of the four species. Interestingly, an intraspecific differential MboI pattern was obtained for the swordfish samples. This pattern was useful to differentiate the two different clades revealed in this species by phylogenetic analyses using several molecular markers. These results indicate the need to strengthen regulations and define molecular tools for combating the occurrence of fraud along the seafood supply chain and show that COIBar–RFLP could become a standardized molecular tool to assess seafood authenticity.