Methods to Increase Consumer Confidence in Premium Olive Oils

In 2007, the U.S. Marshals Service seized 10,939 cases of extra virgin olive oil and pomace olive oil, valued at approximately $628,000, in Long Island City, NY. The oil being sold as extra virgin olive oil and pomace olive oil was actually soybean oil.

Extra virgin is the top grade of olive oil, according to standards established by the International Olive Council (IOC) and the United States Department of Agriculture (USDA). It demands a premium price, as much as 10 times that of a lower grade. This price differential is the primary motivation for adulteration and/or counterfeit labeling at any point at which a sale of the oil occurs.

A recent study1 showed that greater than 65% of bottles labeled imported extra virgin olive oil are either a cheaper grade of olive oil or are adulterated with another type of oil. Given that the U.S. imported over 275,000 tons of these oils from the 2008/2009 crop year,2 a seizure of this size is likely only a small portion of adulterated products reaching the consumer.

The growing awareness of U.S. consumers as to the perceived health benefits of olive oil consumption has contributed to both domestic production and import levels. Olive oil imports in 2009 were 163% of what they were in 1999.3 This growth rate is expected to accelerate. Sadly, higher premium prices to the consumer do not guarantee value; the previously mentioned UC Davis study1 identified many leading brands that produced samples that did not meet this highest-quality grade.

In response to consumer awareness and producer demand, the USDA recently published revised standards for the grading of olive oil. These new standards, which became effective October 25, 2010, replaced standards that had been in effect since 1948.

In the 62 years between revisions, technologies have changed. Advanced, low-cost, and easy-to-use instrumentation is now readily available all along the supply chain. The producer, the bulk handlers, the distributor, and the retailer all can now do on-site testing of their products, demonstrating to the consumer the premium value of their purchases.

Since U.S. extra virgin olive oil is the target of counterfeiters, it is useful to examine the standards for that product. While there is not presently a USDA-sanctioned certification program available, according to the USDA:

U.S. Extra Virgin Olive Oil is virgin olive oil which has excellent flavor and odor (median of defects equal to zero and median of fruitiness greater than zero) and a free fatty acid content, expressed as oleic acid, of not more than 0.8 grams per 100 grams, and meets the additional requirements as outlined in §52.1539, as appropriate.

There are optional tests that can be performed, but the required analysis on each lot includes but is not limited to the following:

  • Determination of the organoleptic characteristics (taste and odor)
  • Determination of free fatty acid content (as oleic acid)
  • Determination of peroxide value
  • Determination of absorbency in the ultraviolet
  • Determination of the fatty acid composition
  • Trans-fatty acid
  • Desmethylsterol composition (% total sterol)
  • Total sterol content
  • Stigmastadiene.

Taste and odor are objective evaluations usually done by trained testers with vast experience. Other tests are done by skilled technicians, and some stipulate the use of advanced methods such as gas chromatography.

There are also other bellwethers of changes in quality, taste, and odor. The greenish-yellow tint and distinctive fruity aroma of extra virgin olive oil stems from the high level of chlorophyll and other volatiles extracted from the olive. As oil is processed to lower grades, the concentrations of these key constituents change. Changes in chlorophyll content and loss of volatiles are good measures of product variation.

Easy-to-use, low-cost, portable spectrophotometers/fluorometers capable of wide-spectrum analysis are effective tools for the relatively unskilled user. Product variations that may not be reliably detected by the examiner may become evident when comparing the visible/near-infrared (VIS/NIR) spectrum and fluorescence attributes of two samples.

The following example uses a spectrophotomer/fluorometer with a handheld Lab-Navigator interface. The “plug and play” VIS-NIR NavSpec+ spectrophotometer (Forston Labs, Fort Collins, CO) measures and displays between 350 and 980 nm and has a built-in fluorometer with two selectable excitation wavelengths (405 and 500 nm).

The USDA absorbance measurements are made in the UV range; UV spectrophotometers with these capabilities are also available from Forston Labs and others. Using the fluorometer of the NavSpec+ as a secondary method, users can make a comparative measurement of chlorophyll content at their point in the distribution chain. At-point-of-transfer testing at increased intervals, verified as needed by formal analysis of questionable product, increases the probability of detection of adulterated products. By increasing the risk of detection to counterfeiters, the purity of product throughout the supply chain is also increased.

A sample of olive oil examined in the VIS/NIR range for absorption creates peaks near 410 nm and 665 nm. A comparison of extra virgin olive oil and those of lesser grades shows that the spectra are an indicator of purity. Natural variations in sources occur; therefore VIS/NIR measurements of comparable samples may be somewhat misleading. A higher level of confidence in the test results can be achieved by spending a few minutes testing the same samples using the fluorometer function of the instrument.

A study in 2000 suggested that fluorescence spectra likely provide a simple, rapid test for adulteration of extra virgin olive oil.4 The unadulterated extra virgin olive oil has a distinctive spectra and, as the oils are further processed to lower grades, the change in the spectra can be dramatic.

The following example demonstrates a fast, simple method that requires virtually no sample preparation, and that provides three points of reference for comparison in a graphical form. The method can be performed with handheld instrumentation by virtually any operator using known grades as reference standards.

Results that are comparable to those of the reference standard provide a significant level of confidence that the product is as it is purported to be. Results that are questionable raise a red flag, indicating that confirmation from a full-range testing laboratory will probably prove a lesser-grade product is in hand.

The following example tested samples of:

  • Extra virgin olive oil from California Olive Ranch™ (Oroville, CA)
  • 100% soybean oil
  • Extra virgin olive oil adulterated 50% by volume with soybean oil
  • “100% Pure All Natural” olive oil composed of “refined olive oils and virgin olive oils” from Filippo Berio (Lucca, Italy).

Figure 1 - Absorption vs wavelength.

A sample of each oil was first tested, comparing the sample absorption versus wavelength between 380 and 950 nm. The values vary considerably at 410 and 665 nm, as seen in Figure 1. At these wavelengths, the absorption values drop, as does the content of the extra virgin olive oil. This follows the removal of chlorophyll and other volatiles during processing under pressure and the inherent differences in oils such as soybean.

An additional point of comparison can be made using information from the previously mentioned study of the fluorescence of oils. The study showed that all the oils tested (except for extra virgin olive oils) showed a strong fluorescence band in the 430–450 nm region. The study examined olive, olive residue, refined olive, corn, soybean, sunflower, and cotton oils.

Figure 2 - Fluorescence at 405 nm.

Measuring the fluorescence of the same oil samples using the 405-nm excitation capabilities of the NavSpec+ and examining them over the same 430–450 nm range demonstrates similar results (see Figure 2). The extra virgin olive oil fluoresces very little over the range, while any adulteration or variation in type of oil results in a higher fluorescence value.

Comparing Figures 1 and 2, it is easy to see that the oils are chemically different from each other and in ways that would be expected. This simple, easy-to-use procedure, which requires virtually no sample preparation, places a high level of analytical ability in the hands of virtually any user. While not 100% definitive, the results obtained using a spectrophotometer/fluorometer to compare oil samples are valuable not only to distributors but to consumers.

High prices associated with consumer demand for quality products and the magnitude of annual imports and the costs associated with them require reliable tools that provide assurance to buyers. Simple, accurate, and economical testing methods at multiple points along the distribution chain increase consumer confidence.


  1. University of California at Davis. Tests indicate that imported “extra virgin” olive oil often fails international and USDA standards; Jul 2010.
  2. International Olive Council, Market Commentary; Jul 2010.
  3. North American Olive Oil Association; Chairman’s Report; Jan 2010.
  4. Kyriakidis, N.; Skarkalis, P. J. AOAC Int. 2000, 83(6).

Mr. Zelenak is President, Forston Labs, 212 W. Mountain Ave., Fort Collins, CO 80521, U.S.A.; tel.: 800-301-1259, ext. 100; e-mail: A copy of the new USDA standards can be found at