The fast-growing global seafood industry is under close scrutiny from consumers after recent concerns about labeling and the discovery of the use of cheaper substitutes. High standards are expected and so transparency in the supply chain is becoming increasingly important. With updated and amended regulations becoming tighter, the demand for analytical testing in the seafood industry to prove safe and authentic products is growing.
Unprecedented Global Demand
Average annual consumption of seafood per person worldwide increased from 19.3 kg to 20.5 kg between 2014 and 2017. This rate has more than doubled in the past 50 years due to a shift in consumer preference and a better understanding of the health benefits of eating seafood, including that it is a good source of high quality protein and other essential nutrients, particularly omega-3 fatty acid. However, mislabeling and species substitution (using cheaper alternatives) are widespread throughout the industry and have led to product recalls which have seriously impacted brand reputation and the reputation of the food industry as a whole. It has also contributed to an increase in the risk to health due to allergies.
In more recent years, consumers have shown a growing awareness and rising concern for what they are purchasing, including how, where and when their seafood was harvested and or produced. These concerns are a driving force for enacting legislation and developing traceability systems to assess quality and safety throughout the seafood supply chain. Increasingly, analytical testing at various stages of the supply chain is used to ensure that products are authentic and safe.
State-of-the-Art Technology for Species Identification
The following techniques use the latest developments in technology and are now found regularly in the seafood industry to identify origin of products, ensure accurate labeling and to reduce the risk of allergic reactions.
Fisheries and aquacultures are heterogenous in terms of species and food products. With the high perishability of seafood it is often processed before reaching the consumer. Because of this it potentially creates a situation of species substitution, which is difficult to morphologically distinguish. Deoxyribonucleic acid (DNA)-based polymerase chain reaction (PCR) methods, including DNA sequencing, restriction-fragment length polymorphism (RFLP), randomly amplified polymorphic DNA (RAPD), multiplex-PCR, quantitative PCR (qPCR), and simple sequence repeats (SRR) or micro-satellites1 are widely used to identify seafood species. However, these methods are limited to detect only known DNA sequences, are cost intensive, and time consuming.
These constraints can be overcome by using Next Generation Sequencing (NGS). This innovative technique, which looks at DNA-based content, is now frequently used and has the significant benefit of allowing the identification of multi-species in complex/mixed samples, or even in the case of closely related species, simultaneously. NGS is now the standard approach in the food inspection field.
DNA integrity can be damaged as a result of processing, such as acidification and thermal treatment when producing finished products. When tested, this can lead to non-specific identification. Thus, a proteomic tool obtained by matrix-assisted laser desorption/ionization – time of flight mass spectrometry (MALDI-TOF MS) – can be introduced as an alternative technique.
This method involves characterizing protein and peptide patterns for seafood authenticity and then comparing them with a database of spectral libraries of individual species. With automated data acquisition and powerful bioinformatic processing, the proteomic technique takes advantage of high-throughput capability, speed, sensitivity, and robust quantification2.
Parvalbumin (PRVB) isoform can be selected as a key for a protein marker for fish species identification3. This biomarker is applicable for:
- Identification if any member from the Merlucciidae family is present in the sample
- Discrimination between the genera Merluccius
- Classification of hake species into two groups according to their geographic distribution: American hake or Euro-African hake, and
- Finally, the combination of the presence/absence of eight other peptide biomarkers allowing the unambiguous identification of any specific species from the Merlucciidae family
PRVB is not only interesting as the protein biomarker, is also considered the major fish allergen. Therefore, analysis targeting this protein has a double application – both for species identification and for food safety purposes4.
Besides proteomic, lipidomic analysis reveals the phospholipid profile for fish authenticity and is increasingly studied using multiple analytical techniques, including nuclear magnetic resonance (NMR) spectroscopy, gas chromatography (GC) and liquid chromatography (LC) mass spectrometry, etc. The multidimensional mass spectrometry-based short gun method is one of the main analytical platforms in current lipidomic studies.
Nevertheless, the experimental operation of these methods is complicated, laborious, and time consuming. A more recent innovation applies rapid evaporative ionization mass spectroscopy (REIMS) with an intrinsic coupled intelligent knife (iKnife). This technology is based on the production of gaseous ions, mostly from fats/lipids and especially phospholipids. This has been used in routine clinical trials and more recently has been extended to identify food authenticity because it offers real time analysis and without the need for sample preparation5.
Recently, Song et al. developed and optimized a method by using the REIMS system with iKnife to discriminate between salmon and rainbow trout6. This efficient method is in urgent need due to claims that in China rainbow trout is often labeled as salmon. This particular case has aroused widespread attention because of the potential consumer health impact; rainbow trout can be infected with fish parasites, which can induce human hepatic disease and cholangiocarcinoma. REIMS continues to be studied for its potential to be used in other situations too, such as determining line-caught and trawler-caught seafood.
Demand for Stricter Control
Together, consumers, governments, and the food industry are demanding stricter control and tighter monitoring of seafood authenticity, along with its safety and quality.
The future of analysis for seafood authenticity depends upon NGS, proteomic, and lipidomic techniques. These require both reference databases and advanced statistical tools, such as Hierarchical cluster analysis (HCA), principle component analysis (PCA), and partial least squares (PLS) for result interpretation, whether the sample is likely a food fraud or not7.
The advances in technologies and instrumentations for seafood authenticity testing show promise, however issues of method validation and harmonization suggest they should be modified and refined at the laboratory stage prior to implementation in the industry. Furthermore, inter-laboratory comparisons and certified reference material should be addressed in order to guarantee the laboratory performance.
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1Bohme K., Mata-Calo P., Barros-Velazquez J. et al. Review of recent DNA-based method for main food authenticity topic. J. Agric. Food Chem. (2019); 67: 3854-3864.
2Verrez-Bagnis V., Sotelo C.G., Mendes R. Method for seafood authenticity testing in Europe. Bioactive molecules in food (2019); 2063-2117
3Carrera M., Canas B., Gallardo J.M. Fish authenticity. Proteomics in foods: principles and applications (2013); 205-222.
4Elsayed S., Bennich H. The primary structure of allergen M from cod. Scandinavian journal of immunology (1975); 4: 203-208.
5Black C. Chevallier O.P, Hauhhey S. et al. A real time metabolomic profiling approach of detecting fish fraud using rapid evaporative ionization mass spectrometry. Metabolomics (2017); 13 (153): 1-13.
6Song G., Zhang M., Zhang Y., et al. In Situ method for real-time discriminating salmon and rainbow trout without sample preparation using iKnife and rapid evaporation ionization mass spectrometry-based lipidomics. J. Agric. Food Chem. (2019); 67: 4679-4688.
7Fiorino G.M., Garino C., Arlorio M. et al. Overview on untargeted methods to combat food frauds: a focus on fishery products. J. Food Qual. (2018); 3: 1-13.