A DNA ANALYSIS TO IDENTIFY THE CORRECT MACKEREL SPECIES, EVEN IN PROCESSED PRODUCTS
The appointment with news testifying to seizures and fines in the fish market in the context of controls against food fraud is now daily. Many of these are precisely due to incorrect, voluntary or not, product labelling.
An incorrect assignment of species determines a fraudulent communication of the product in terms of nutrition, quality and geographical origin without underestimating the sustainability and economic aspects.
The mackerel case
An example is mackerel, which in nature is represented by several recognized species: Atlantic mackerel or just mackerel (Scomber scombrus), chub mackerel or Pacific mackerel (Scomber japonicus), Atlantic chub mackerel or Tinker mackerel (Scomber colias) and blue mackerel (Scomber australasicus).
The four species are very similar to each other, so much so that S. colias has for years been considered a subspecies of S. japonicus, Scomber japonicus colias precisely. It is still often marketed as Scomber japonicus colias, but for correct labelling, a clear identification of one of the two species is necessary.
In addition, the four different species share many DNA sequences which therefore do not discriminate and prevent the classic methods of DNA analysis (DNA barcoding) from identifying and confirming the species to which a mackerel sample belongs.
The analysis is even more complex when we want to check processed products such as cans of mackerel in oil or in brine, or fishmeal or fish oil. This is because the manufacturing processes (heat, homogenization, etc.), but also the conservation in oil or brine, induces an invasive degradation of the DNA which is very fragmented and not always so informative.
A tailored analysis
Our team of experts has conducted research to develop a diagnostic system, based on genetic analysis, to identify the membership of species also of semi-finished or already packaged mackerel products.
The main objective of the study was to develop a laboratory method that would make it possible to distinguish between the main commercial species of mackerel: Scomber colias, S. japonicus, S. australasicus and S. scomber.
In addition, to identify DNA isolation methods that allow obtaining a sufficient quantity of genetic material that can be analyzed, regions common to different species have been identified that were suitably small to be efficient in case of degraded DNA and with a sufficiently discriminating DNA sequence.
The method has been validated on several products mainly of S. colias and S. japonicus, resulting in being efficient even in products of different processing and preparation (cans in oil, natural mackerel, mackerel fishmeal and mackerel fish oil).
This approach certainly represents an innovative and advantageous tool for producers and control bodies in order to increase the safety and traceability of the mackerel chain.