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Detecting Adulteration in Olive Oil
by Sharon Palmer
There is no other food quite like olive oil. There is also, apparently, no better motivator throughout history than the chance to make a quick buck. In the case of extra virgin olive oil, it has been prized throughout the ages for possessing unique qualities that delight the senses based on its nutritional, medicinal, cosmetic, and even ceremonial value. As a result, it is one of the most expensive—and also one of the most adulterated—food products in recorded history.
The earliest written mention of olive oil, on cuneiform tablets at Ebla, Syria, in the 24th century B.C., for instance, describes royal inspectors visiting olive oil crush mills in search of fraudulent practices. The Romans also developed strict regulations concerning olive oil. According to one industry resource into the history of olive oil, the Roman amphorae, or jars where the olive oil was kept, were carefully inscribed to show where the olive oil was produced, who produced it, when it was produced, and the quantity and quality of the product. In more recent times, modern science has extolled the virtues of extra virgin olive oil for its nutritional value, high antioxidant (including vitamin E) content, and its low saturated fat when compared to other oils. That, in turn, has led to a fraudulent business estimated by one law enforcement agency to rival the profits of cocaine without the high risk of being caught. Indeed, olive oil adulteration continues to attract global attention in a variety of media, from major news exposes and magazines to research labs and courtrooms. Researchers at the University of California, Davis, for instance, released the findings of a now famous 2010 study showing that more than two-thirds of the extra-virgin olive oil sold in California is neither extra-virgin nor in some cases even olive oil, as the real oil is often adulterated with cheaper, more available oils.
In still another recent venue reported by the Olive Oil Times in November 2013—in this instance a Washington D.C. superior courtroom—olive oil played a starring role in a suit filed and won by a consumer against a local grocer “for violating the D.C. Consumer Protection Procedures Act (CPPA) by selling Pompeian brand olive oil mislabeled as ‘extra-virgin.’” According to the UC Davis study mentioned earlier, the Pompeian brand of olive oil was already known to be adulterated and the consumer simply purchased the product in order to file the suit for some quick cash. As outrageous as that lawsuit and its outcome appears, such reports continue to sound a clarion call for the oil industry and government regulatory agencies to take the necessary steps to guarantee the safety and purity of extra-virgin olive oil. Equally important is the need to restore the sense of trust consumers have lost in big olive oil brands and retailers who continue to sell adulterated products at a huge cost to consumers in terms of both money and, at times, their health. In 1981, more than 600 people died because of adulterated olive oil that contained rapeseed oil and aniline, causing a huge scandal.
Even now, however, some authorities continue to rely on little more than their senses to detect olive oil adulteration. Unfortunately, taste or smell may not be sensitive enough to detect more sophisticated adulteration or mislabeling techniques that fraudsters employ. Less expensive oils such as corn, safflower, sunflower, and sesame oils that are commonly used to “cut” olive oil share many of the same properties, only in different proportions, and are impossible to detect without the use of modern analytical equipment. Unfortunately adulteration remains a big issue. As the olive oil industry looks for new ways to detect and deter criminal activity, increasingly they are looking to science for answers.
Science Supplants the Senses to Uncover Fake Olive Oil
It was not until the 1950s that science started to replace the senses in detecting non-authentic botanical oil substitutes in olive oil. Even with the development of modern gas chromatography/mass spectrometry (GC/MS), and high performance liquid chromatography (HPLC/MS), developing a quick, reliable, and cost-effective analytical approach to identifying the adulteration of olive oil with cheaper oil substitutes has proven to be both a slow and expensive process.
The main reason has to do with oil’s composition. Olive oil and other oils are primarily composed of triacylglycerols, which are highly concentrated stores of metabolic energy also known as dietary lipids. These molecules are derived from the esterification of three fatty acid molecules with a glycerol molecule, and they determine the fatty acid composition of oils.
While olive oil and its substitutes all contain fatty acids, olive oil possesses more than twice the amount of oleic acid. Conversely, olive oil possesses considerably less linoleic and linolenic acids than the cheaper additives. While measuring the ratio of these acids to oleic acid in olive oil is an effective way to detect adulteration of extra virgin olive oil, there are still some major drawbacks. Chief among them is the extensive amount of time that is needed for sample preparation, method development, and derivation.
A Faster Methodology
Fortunately, there is a new way to detect and confirm the authenticity of olive oil in a matter of seconds without hours of prep time. Using a real-time screening technology known as Direct Sample Analysis (DSA) integrated with Time-of-Flight Mass Spectrometry (TOF), the new process eliminates the need for chromatography and requires minimal or no sample preparation in rendering reliable mass spectra results in seconds.
For example, when comparing olive oil and soybean oil, the two oils were diluted in a 1 percent solution of isopropanol with 10 millimeters of ammonium acetate. The oils were then mixed in different proportions to simulate the contamination of olive oil with soybean oil at different percentages ranging from 5 percent and 10 percent to 25 percent and 50 percent. A small amount of each sample was then pipetted directly onto the stainless steel mesh of a DSA/TOF system for ionization and analysis. The DSA/TOF parameters for the experiment featured a corona current of 5 microampere with a heater temperature of 350 degrees Celsius. The TOF MS was then run in negative ionization mode with flight voltage of 8000 volts and capillary exit voltage of -120 volts for the analysis. Mass spectra were acquired in a range of mass-to-charge ratio 100 to 700 at an acquisition rate of 5 spectra/second. In order to realize the highest test accuracy, the TOF instrument was calibrated before each analysis. All samples were analyzed within 30 seconds, and results were immediately observable. Using DSA/TOF showed that the fatty acids mentioned earlier (oleic, linoleic, and linolenic) were all present in both olive oil and soybean oil. However, their relative proportion in each of the oils was quite different. The response ratio of linoleic acid to oleic acid was measured at 0.18 and 1.86 in olive oil and soybean oil, respectively. The response ratio for linolenic acid to oleic acid, meanwhile, was 0.017 and 0.29 in olive oil and soybean oil, respectively. That means the higher response ratio for linoleic and linolenic acid to oleic acid can, in fact, be used to detect adulteration of olive oil using DSA/TOF technology with an error of less than 5 parts-per-million (ppm).
In reviewing the results of the olive oil rapid screening experiment using a PerkinElmer AxION DSA with an AxION 2 TOF, it shows the higher response ratio for linoleic and linolenic acid to oleic acid in olive oil is an immediate and reliable factor in detecting oil adulteration. The mass accuracy of all measurements, in fact, was less than 5 ppm with external calibration.
Equally important is what the DSA/TOF experiment means for the olive oil producers, their customers, and global consumers. In addition to helping the olive oil industry restore its brand image and public faith in its product, employing DSA/TOF technology can eventually help to save lives as well as billions of dollars that are now needlessly spent on fraudulent and sometimes dangerous olive oil.
Palmer is food segment leader at Perkin Elmer. Reach her at Sharon.firstname.lastname@example.org.
- Tom Mueller, Extra Virginity: The Sublime and Scandalous World of Olive Oil, (W. W. Norton & Company, 2013), pp. 10, 29. See also, http://www.whyoliveoil.com/olive-oil-world/
- Sally Errico,”Olive Oil’s Dark Side,” The New Yorker (February 8, 2012), http://www.newyorker.com/online/blogs/books/2012/02/the-exchange-tom-mueller.html
- http://www.whyoliveoil.com/adulteration/. See also, http://articles.latimes.com/2010/jul/07/business/la-fi-olive-oil-20100707
- Kristen Michaelis, “How to Tell if Your Olive Oil Is Fake,” Food Renegade (December, 2013), at: http://www.foodrenegade.com/how-tell-if-your-olive-oil-fake/
- Annibal D.P.N. Fasciotti, “Optimization and Application of Methods of Triacylglycerol Evaluation for Characterization of Olive Oil Adulteration by Soybean Oil with HPLC-APCI-MS-MS,” Talanta (2010)81:1116-1125.
- Avinash Dalmia and George L. Perkins, “Rapid Measurement of Olive Oil Adulteration with Soybean Oil with Minimal Sample Preparation Using DSA/TOF,” Application Note (PerkinElmer, 2013).