Detecting Adulteration in Olive Oil

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.