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The global market regularly leads to new challenges. One of the recurring challenges is ensuring the transparency of goods in the global market.
The authenticity and traceability of produce is important for a great number of reasons including ensuring that financial transactions and the movement of goods are in accordance with the law.
Until recently, traceability of goods and transactions associated with the goods has been based on paper documents/digital records. As the opportunity to verify origin by analytical methods (isotope testing) has emerged in recent years there has been movement in the global market to utilise this as additional evidence that products are legitimately declared with respect to their origin.
Determination of origin using the stable isotope ratios of the bioelements has been demonstrated to be successful across a great number of products including wine (Förstel 1994), olive oil (Angerosa 1999), honey (Padovan 2003), beef (Boner 2004) and milk/ butter (Rossmann 2000).
Based on the knowledge that different geographical regions exhibit different isotope ratios in water, it is fair to reason that animals living in those regions will take up the water in their tissues. This is particularly evident in freshwater fish like sturgeon (Acipenser) and their caviar.
As part of the initial feasibility study supported by the Customs Criminal Office in Cologne, 33 samples of caviar from different provenances were used to demonstrate that the origin of caviar could be determined by stable isotope analysis. Above all, the most significant outcomes were the differences between European and non-European caviar in the various breeding/production styles. The efficacy of the isotope method was confirmed in a blind test.
As part of the analysis, the oxygen (18O/16O) and hydrogen (D/H) isotope ratios were determined by analysis of the tissue water derived from the caviar using freeze-drying. These isotope ratios alone offered the ability to differentiate the origins of the caviar over long distances, such as Iran vs. Kazakhstan or the indeterminate region of the Caspian Sea (figure 1). Caspian Sea origin is defined as ‘indeterminate’ because there is not always clear differentiation in the various regions of the Caspian Sea.
In detail, caviar samples from Iran show significantly enriched 18O/16O and D/H isotope ratios, whereas samples from Kazakhstan show significantly depleted 18O/16O and D/H isotope ratios.
In fact, measurement of the isotopes of water from caviar allows differentiation between European countries (Germany, France, Italy and Bulgaria). It must be noted that, despite the great difference in geography, samples from Azerbaijan have similar 18O/16O and D/H isotope ratios to samples in Italy in France, though they are significantly different to samples from Germany and Bulgaria.
It is therefore possible to conclude that the origin of caviar in Europe can be determined with the help of the stable isotopes of water.
As the discrimination between Azerbaijani and French caviar is not always possible using the isotopes of water alone, it is therefore necessary to differentiate the caviar by what the sturgeon eat. The stable isotopes of carbon (13C/12C), nitrogen (15N/14N), and sulfur (34S/32S) are a reflection of the dietary sources of carbon, nitrogen and sulfur the sturgeon consume.
As a rule of thumb, nitrogen ratios from the crude protein of caviar are typically enriched above +8‰. This is because sturgeon (Acipenser) are omnivores and tend to consume organisms higher in the food chain (Minawaga 1984). It is a well-documented phenomena that as you go up a food chain, nitrogen ratios tend to be enriched. This principle is used in ecology to determine the position organisms have in a food chain.
The nitrogen isotope ratios in caviar tend to range between +8‰ to +15‰ and the carbon isotope ratios tend to range between -17‰ to -25‰ (Rehbein 2008), (Figure 2). Information from these isotopes allowed for discrimination between Iranian and Kazakhstani caviar in the Rehbein study, though this was not replicated in the Agroisolab study. The most likely reason that this information did not offer discrimination in the Agroisolab study was that there were only two or three reference samples from Kazakhstan and Iran at the time of the project, which were not enough to show the general trend for either country. Using the isotopes of only nitrogen and carbon appears to allow for the grouping of European caviar samples (figure 3). Therefore, these isotope ratios are only used as additional indication of origin.
The sulfur isotope ratios (34S/32S) give good contrast for determining origin. It can be concluded that all non-European caviar samples show relatively depleted 34S/32S isotope ratios (<10‰), whereas all European caviar samples have enriched 34S/32S ratios above +12‰.
In combination with the isotope ratios of water, especially the D/H ratios, this results in significant differentiation possibilities for various origins of caviar. Meaningful differentiation of European caviar can be acheived for regions in Germany, France, Italy and Bulgaria against non-European caviar samples. Non-European caviar can, with the help of D/H and 34S/32S isotope ratios, be broken down into two different general origins: (Iran, Azerbaijan) and (Kazakhstan, Caspian Sea).
It is particularly noteworthy that stable isotope ratios allow for caviar of European origin to be broken down into the different countries. As only two samples from Italy show signatures that are consistent with non-Italian samples, it is conceivable that these two samples were from Northern Italy, explaining the overlap of signatures with other European countries that are close by.
Agroisolab has caviar isotope data from the following countries:
• Caspian Sea
Case study: Cologne customs investigators discover caviar smuggling using isotope analysis
The German Customs Investigation Office food service seated in Cologne discovered a large-sclae tax avoidance operation in Pfungstadt, Germany. The Treasury were witheld € 150,000 on customs duties and import turnover tax.
Caviar products being sold were declared to have originated from a farm in Germany. However, the producer in fact obtained the caviar from the Caspian Sea and used the farm as a front to avoid paying the taxes and duties on the import of the Caviar.
After evaluating the extensive amount of evidence seized, it was clear that the convicted person had sold more than 100kg of beluga caviar at several top restaurants throughout the course of the year.
Under the investigation of the Customs Authority, the owner of the breeding facility could neither provide proof of the legal acquisition of the protected animals nor information about the origin of the caviar. Additionally DJE investigators used stable isotope analysis to demonstrate the caviar did not originate from the farm, but from the Caspian Sea.
The perpetrator was sentenced to prisonfor one year for the offence. The sentence could not be suspended as the convicted person was already in custody for other offences.