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ANALYTICAL CHEMISTRY


E


ggs from caged hens labelled as free-range, vegetables wrongly claimed as organic, premium price honey adulterated with


corn syrup, fancy French wine diluted with water and bootleg spirits topped up with cheap but deadly industrial alcohol. Food fraud affects about 10% of


global food supply, with an estimated annual value of around $40bn. Over a four-month period earlier in 2017 alone, a joint Europol-Interpol operation seized €230m of fake food and drinks in a crackdown on the illicit trade. Complex global food supply networks are increasing the opportunities for fraud, affecting the reputations and revenues of legitimate food companies – and posing a health and safety risk. Cases such as the 2008 discovery


of toxic melamine added to infant formula in China, and the 2013 British horsemeat scandal, have raised concerns about the food on our plate. Media interest in the recent European egg scandal is a case in point. In response, legitimate food producers are resorting to a number of various tactics to prove product authenticity, provenance and supply chain integrity in the battle to beat the fraudsters. One emerging tool looks to chemical fingerprints, which is gaining popularity, used in industries from eggs to honey and dairy, and even seafood. Western Australia- based Source Certain International is a forensic sciences firm that uses chemical technology to verify the integrity of the supply chain. ‘[Our own] fingerprints contain characteristic patterns that can be used to identify you individually,’ says executive chairman Cameron Scadding: ‘In line with this analogy, we can determine the chemicals in a food and build a characteristic fingerprint with these chemical measurements.’ Every food will have a unique


profile based on the levels of biochemical substances, trace elements and isotopes, elaborates David Ellis, senior experimental officer at the University of Manchester’s School of Chemistry. This fingerprint can be used to identify adulterated, falsely labelled and counterfeit food because the adulterants and other substances will present a different chemical


profile, Ellis explains. As such, chemical fingerprints can maintain integrity along the supply chain. There is also the further attraction that chemical fingerprints are essentially impossible to copy, and don’t rely on packaging or labels to prove authenticity, both of which can be tampered with, copied or falsified, says Scadding. ‘Chemical fingerprinting goes to the authenticity of the actual food and is independent of any associated label claims.’ A number of technologies


10%


of global food supply is estimated to be af- fected by food fraud


€230m


value of fake food and drinks seized in four months earlier in 2017 in a global crackdown by Europol-Interpol


Chemical fingerprints are virtually impossible to copy, and don’t rely on packaging or labels to prove authenticity, both of which can be tampered with, copied or falsified


>200


are used to determine chemical fingerprints. NMR spectroscopy, for example, focuses on the magnetic properties of certain nuclei to establish the physical and chemical properties of atoms in a molecule. Food fraud often employs site- specific natural isotope fractionation (SNIF) NMR, which looks at the relative and specific locations of hydrogen’s stable isotope, deuterium, in a molecule. IR and Raman spectroscopies, alongside chemometrics to translate the data, also rely on spectra to determine the (bio)chemical characteristics of food samples. Some forms of spectroscopy can even detect a chemical fingerprint through the packaging, which Ellis says is a ‘big bonus’ for foodstuffs.


Mass spectrometry is another


Signature compounds, in combination, found to be unique to honey made from New Zea- land’s manuka plant


technique gaining popularity for determining the chemical profile of foods. Scientists from the Czech Republic and Spain, for instance, have used liquid chromatography coupled with high-resolution MS to distinguish between saffron certified with the EU’s Protected Designation of Origin (PDO) from Spain’s La Mancha or Aragon, Spanish saffron that does not have the PDO certificate and mislabelled saffron. After analysing 44 samples to compare metabolomic chemical fingerprints, they found that more than 50% of Spanish-labelled samples were fraudulent: neither grown nor processed in Spain. Although the exact origin of the mislabelled saffron was uncertain – likely to be Morocco, Iran or India – the scientists were able to match the legitimate chemical fingerprints with the La Mancha samples and determine that glycerophospholipids and their oxidised lipids were the best molecular markers for provenancing saffron.


In a similar vein, beekeepers and scientists in New Zealand have spent years attempting to find the unique chemical signature of the country’s native manuka honey, often targeted by fraudsters because of its premium price tag. Several overseas markets in the past have questioned the authenticity of some honey labelled as New Zealand manuka honey, and earlier this year, jars with this label were removed from UK supermarket shelves after fakes were discovered. The Unique Manuka Factor Honey Association (UMFHA) recently announced the findings from more than five years of scientific research, revealing that the presence of the compound leptosperin determines the authenticity of manuka honey. More than 200 signature compounds, in combination, were found to be unique to honey made from New Zealand’s manuka plant. John Rawcliffe, administrator of the UMFHA – who calls the project ‘ground breaking’ – says the research involved collecting different New Zealand plant species over three harvest seasons, with samples coming from different geographies around the country. A chemical fingerprint was generated using ultra performance liquid chromatography- high resolution MS, he says, while the research also involved matching nectar chemicals with honey chemicals for traceability. He believes the results will not only protect New Zealand manuka honey producers, but also give consumers ‘greater confidence’ in their honey purchases. The work is also relevant for cheaper honey adulterated with cane sugar or corn syrup. In this case, isotope ratio mass spectrometry (IRMS) measures the variation in abundance of the isotopic ratios of carbon, nitrogen, sulphur, oxygen and hydrogen. According to a paper by Katryna van Leeuwen and coworkers (Comprehensive Reviews in Food Science and Food Safety, 2014, 13(5), 814), this ‘powerful technique’ has been ‘widely used [in authenticity and traceability testing] due to the high precision of the method, the requirement for small samples, and the fact that the same technique can be used for almost any type of food or beverage’.


IRMS can spot honey with added cane sugar or corn syrup because of subtle differences in


28 09 | 2017


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