Red Gold: the Real Deal?
(February 12th, 2016) A new metabolomic test allows researchers to distinguish between traditional Spanish saffron and its imposters.
Saffron - sometimes referred to as “red gold” - is one of the most expensive spices in the world. It is also one of the most recognisable. The vermillion threads, sprouting three at a time from each purple saffron crocus, are responsible for the golden hue of many a paella, risotto and bouillabaisse.
Unfortunately, the high price fetched by Spanish saffron processed using traditional methods has inspired a counterfeit market, whereby saffron grown in other nations is imported, then packaged and sold as if it had originated in Spain. Recently, researchers at the University of Chemistry and Technology in Prague developed a technique that uses the spice’s chemical fingerprint to verify claims made on the package.
Saffron that is grown and processed in the La Mancha and Aragon regions of Spain, according to traditional practices, is considered to be of the highest quality and is labelled Protected Designation of Origin (PDO). The researchers, led by Jana Hajslova, looked at 44 samples that fell into three categories: PDO Spanish saffron; saffron grown and processed in Spain but not certified PDO; and saffron of unknown origins.
To develop the test, Hajslova’s group identified metabolites that are unique to saffron. They extracted as many of these metabolites as possible to obtain what Josep Rubert, the study’s first author, describes as an “instantaneous snapshot” of the sample’s metabolome.
The scientists then used liquid chromatography and high-resolution mass spectrometry to separate and characterise the metabolites. Once the specific molecules had been identified, they applied statistical methods - principal component analysis and orthogonal partial least squares discriminant analysis - to differentiate between PDO and non-PDO saffron.
Hajslova’s group found that the way saffron is processed has the greatest impact on its chemical fingerprint. Saffron processing varies greatly by region and has a strong effect on the spice’s quality. The traditional methods used to produce PDO saffron are both the most desirable and the most expensive. In La Mancha, the hand-gathered stigmas of the saffron crocus are laid over sieves near a source of high heat, such as a stove, fire, or hot coals, often approaching 70 °C. Using this method, saffron can be dehydrated in as little as half-an-hour.
As the saffron is heated, its lipids begin to oxidise. The high heat used for dehydration in La Mancha accelerates lipid oxidation; as a result, saffron processed in this region will have a much higher incidence of oxidised lipids than saffron produced elsewhere. The cheapest and lowest-quality saffron is air-dried, resulting in little to no lipid oxidation.
The researchers found that glycerophospholipids and their lipid oxidation compounds could be used as a chemical fingerprint to label saffron samples of known origin with complete accuracy. Upon further inspection, the test showed a prediction ability of 85%, meaning that it was able to definitively label saffron of unknown origin at a rate of 85% accuracy.
Using this test, the researchers determined that over half of the saffron in their samples was fraudulent. If this figure seems high, consider the fact that between 1997 and 2013, Spain produced about 2,813 kg of saffron per year, yet exported over 12 times that amount. Over 92% of Spanish-labelled saffron is estimated to be counterfeit. The spice is grown and processed cheaply in other countries, such as Iran, India, or Morocco, then brought to Spain for packaging and sold on the worldwide market.
Rubert hopes that a metabolomics test will be used to regulate saffron sales in the future, although the validation measures will need to be improved and simplified before this can occur. The study was part of a larger effort through COST Actions, a scientific networking initiative, to apply interdisciplinary approaches like metabolomics to problems in science and technology. In the future, it is likely that scientists will use similar techniques to improve the traceability of many different food products.
“It seems that, sooner or later, food authenticity will be focused on metabolomics,” says Rubert. “In fact, European projects, conferences and researchers are currently focused on food metabolomics and how we can establish it to regulate any product - challenging, but awesome.”
Photo: Crocus sativus by KENPEI (GFDL)