Food adulteration is one of the most serious problems regarding food safety and quality worldwide. Besides misleading consumers, it poses a considerable health risk associated with the potential non-labeled allergen content. Fish and fish products are one of the most expensive and widely traded commodities, which predisposes them to being adulterated. Among all fraud types, replacing high-quality or rare fish with a less valuable species predominates. Because fish differ in their allergen content, specifically the main one, parvalbumin, their replacement can endanger consumers. This underlines the need for reliable, robust control systems for fish species identification. Various methods may be used for the aforementioned purpose. DNA-based methods are favored due to the characteristics of the target molecule, DNA, which is heat resistant, and the fact that through its sequencing, several other traits, including the recognition of genetic modifications, can be determined. Thus, they are considered to be powerful tools for identifying cases of food fraud. In this review, the major DNA-based methods applicable for fish meat and product authentication and their commercial applications are discussed, the possibilities of detecting genetic modifications in fish are evaluated, and future trends are highlighted, emphasizing the need for comprehensive and regularly updated online database resources.

Parvalbumins (PVALBs) are low molecular weight calcium-binding proteins. In addition to their role in many biological processes, PVALBs play an important role in regulating Ca2+ switching in muscles with fast-twitch fibres in addition to their role in many biological processes. The PVALB gene family is divided into two gene types, alpha (α) and beta (β), with the β gene further divided into two gene types, beta1 (β1) and beta2 (β2), carrying traces of whole genome duplication. A large variety of commonly consumed fish species contain PVALB proteins which are known to cause fish allergies. More than 95% of all fish-induced food allergies are caused by PVALB proteins. The authentication of fish species has become increasingly important as the seafood industry continues to grow and the growth brings with it many cases of food fraud. Since the PVALB gene plays an important role in the initiation of allergic reactions, it has been used for decades to develop alternate assays for fish identification. A brief review of the significance of the fish PVALB genes is presented in this article, which covers evolutionary diversity, allergic properties, and potential use as a forensic marker.

The real-time quantitative PCR (qPCR) calibration curves are highly reproducible and allow the generation of specific, sensitive, and reproducible data that can be used for gene quantification. However, it is important to rigorously validate the external calibration curve model in qPCR since absolute quantification is dependent on the standards used. We present a method for standardising qPCR-based quantification of the β-parvalbumin (β-pvalb) gene of Lophius piscatorius, a major fish allergen, using a plasmid DNA (pDNA) calibrator. In parallel experiments, standard curves were generated and compared from the genomic DNA (gDNA) isolated from L. piscatorius and pDNA carrying the target, pvalb. The commutability of pDNA and gDNA calibrators for the quantification of β-pvalb was assessed by employing a TaqMan qPCR, targeting the second intron of the pvalb gene of L. piscatorius. Higher PCR efficiencies, good linearity, and lower standard deviation (S.D.) values were observed with pDNA instead of gDNA calibrants. pDNA calibrants exhibited a lower bias in terms of closeness to the expected value of unknown samples than their genomic counterparts. The assay was specific and sensitive, where the limit of detection (LOD) and limit of quantification (LOQ) were five copies and ten copies per reaction. The short-term stability study of the pDNA calibrants indicated its stability for 60 days at − 20 °C and 30 days at 4 °C. The efficient results indicated a plasmid calibrator as a potential tool for absolute quantification of the pvalb gene and an alternative to conventional gDNA standards.

This study presents a large-scale interlaboratory comparison (ILC) aimed at detecting and quantifying DNA from two European anglerfish (Lophius budegassa, Lophius piscatorius), pike (Esox lucius) and sea bream (Spondyliosoma cantharus) using real-time qPCR. To detect amplification of the parvalbumin genetic marker, single and multiplex qPCR assays using EvaGreen® dye or TaqMan™ probes were used. Genomic DNA isolated from target fish species and an advanced DNA calibrator, gBlocks® gene fragments, were used as standards. The DNA of anglerfish, pike and sea bream as well as their mixtures were analysed together with 14 other non-target fish species. All target fish samples were correctly identified by the participating laboratories. Qualitative assessment of anglerfish and seabream DNA showed an accuracy rate of 100%, while pike DNA achieved a match rate of 99%. Validation of quantitative protocols in four different laboratories consistently achieved z-scores below 2, indicating satisfactory performance and confirming the high degree of similarity of laboratory results. Furthermore, high accuracy and efficiency were demonstrated for the quantification of anglerfish and seabream DNA by triplex qPCR using TaqMan™ probes. Regarding the selected gene marker, the major fish allergenic protein parvalbumin enables indirect detection and quantification of the allergen in the sample. Therefore, the use of proposed protocols can significantly contribute to protecting the health of consumers and to controlling the food market. Graphical abstract