Bookmark and Share

From: Food Quality & Safety magazine, October/November 2010

Testing Olive Oil Authenticity

Analytical tools can help spot subpar oils

by Rob Griffiths

Notice was given in the April 28, 2010, Federal Register that on October 25, 2010, revised U.S. standards for grades of olive oil and olive-pomace oil will become effective, replacing the first edition of the U.S. grade standards, which have been in force since March 22, 1948.1

The new U.S. regulations will institute a testing regime comparable to the one used in Europe for the last 20 years. The acceptable characteristics of olive oil and the relevant methods for determining these were described in the original European Commission Regulation 2568/91. Now a European Union Regulation, 2568/91 has undergone a few minor amendments since its introduction in 1991 and sets out more than 20 analytical values for determining the relevant grade, quality, and authenticity of the olive oil under investigation.

A number of analytical tests can be used to detect whether cheaper oils have been used to dilute pure olive oil.
A number of analytical tests can be used to detect whether cheaper oils have been used to dilute pure olive oil.

Eight grades are defined between the poorest olive residue oil and premium extra virgin olive oil. If any characteristic of an oil lies outside the defined limits, the oil must either be reclassified as a different grade or rejected on quality or authenticity grounds.

Criminal Oil

In Europe, the pressure to develop this regulation came out of the recognition that there would always be suppliers attempting to market low-grade olive oil as a more expensive higher grade or to substitute a portion of the olive oil with cheaper oil such as rapeseed or sunflower. Even with the regulations in place, this temptation still exists, and there have been several high-profile arrests for olive oil adulteration, especially in Italy. In 2008, seven olive oil plants were impounded and some 40 people were arrested in Italy for offenses relating to olive oil adulteration.

Of course, the problem is not restricted to Europe. In June 2010, in the Ontario Court of Justice, LIF Foods Inc. was fined $50,000 for unlawfully importing and selling a quantity of their brand, Porta Villa, labeled as extra virgin olive oil; the oil was actually determined to contain approximately 50% sunflower oil. In 2009, in the Special Commercial Crimes Court in Durban, South Africa, Salvatore Pollizi, owner of the company Ital Distributors, pled guilty to selling fake virgin olive oil under the names of Antico Frantoio and Ulivo.1 The United States has also prosecuted people for similar offenses.

All such adulteration is reprehensible from a commercial perspective, of course, but one cannot underestimate the health risks. Europe, and Spain in particular, can still recall an infamous case from 1981 in which rapeseed oil adulterated with aniline and sold as olive oil in working-class neighborhoods of Madrid caused almost 700 deaths and up to 25,000 injuries.2

Madrid is now home to the International Olive Council (IOC), an intergovernmental organization created by the United Nations that represents the countries responsible for over 95% of the world’s olive oil production, most of which occurs in Italy, Greece, Portugal, and Spain. The IOC is responsible for administering the International Agreement on Olive Oil and Table Olives and for regulating international standards. The new regulation has been introduced largely to bring the U.S. industry in line with international standards. As a consequence, descriptions familiar to U.S. consumers, like “U.S. Fancy” or “U.S. Choice,” will soon be replaced by more internationally recognized terms, and new definitions for olive oil will now be introduced in the U.S.


Of course, a regulation can only go so far in resolving an issue of authenticity. The essential problem in authentication is setting parameters that accurately define the composition of pure, fresh oil. Any oil is a complex mixture of components. These include tri-, di-, and monoglycerides; free fatty acids; saturated, monounsaturated, polyunsaturated, and trans fatty acids; sterols; aliphatic and other alcohols; flavonoids; and a variety of other organic molecules. For oils extracted from the same species of plant, regional variations in climate and soil conditions may affect the levels of some of these components.

That said, each type of oil usually has a fatty acid composition that is indicative of its plant source. So, although it may not be possible to verify authenticity from fatty acid content alone, the presence of the wrong fatty acids can be a very good indication of adulteration. This is true not just of olive oil but of any high-value oil to which a rogue supplier might be tempted to add a cheaper oil.

As noted above, the new U.S. Food and Drug Administration regulations are intended to bring the U.S. in line with the IOC, even though the U.S. is not currently an IOC member. The international standard lists eight grades of olive oil in two primary categories, olive oil and olive-pomace oil or olive residue oil.

The revised U.S. grade standards will list eight grades and will have slightly higher limits for linolenic acid and campesterol, two of the components that are analyzed to determine the purity of the oil. The tests for linolenic acid and campesterol form part of a battery of tests with more than 20 analytes that are measured to assess the purity and quality of every olive oil.

Europe, and Spain in particular, can still recall an infamous case from 1981 in which rapeseed oil adulterated with aniline and sold as olive oil in working-class neighborhoods of Madrid caused almost 700 deaths and up to 25,000 injuries.

Key Components

The testing regime adopted in Europe is essentially the same. The tests conducted can be loosely characterized into tests to determine the quality and authenticity of the oil and to detect the presence of the incorrect grade of olive oil. Free fatty acids, peroxide values, and ultraviolet (UV) determination are tests that ascertain the quality of the oil with respect to hydrolysis or oxidation of the oil.

The fatty acid profile, sterol profile, triglyceride analysis, and glyceryl 2-palmitate determination can be used to detect the presence of oils other than olive.

Erthyrodiol, uvaol, wax, and stigmastadiene analysis are used to detect the presence of olive-pomace oil and/or refined oil in virgin olive oils. Both the U.S. and Europe now require testing under the following broad headings.

Free fatty acids: The free fatty acid content, which is measured by total acidity, indicates quality, because acidity increases with hydrolytic activity, which could be due to poor quality, damaged olive fruit, or microbial activity.

Peroxide value: The oxidation of the oil is determined by the peroxide value, with a high value indicating a poor quality, older, or mistreated oil.

UV determination: The analysis of olive oils at certain UV wavelengths can be used to assess the oxidation of the oils and can also indicate the presence of a refined olive oil in virgin olive oil.

Fatty acids: Fatty acid composition is a useful indicator of purity or the presence of oils other than olive oil. High levels of trans fatty acids can indicate the presence of refined olive oil or other refined vegetable oils in a virgin olive oil.

Glyceryl 2-palmitate: Additional information is gained by determining which fatty acids are located at the 2-position (middle) of the triglyceride. High levels of saturated fatty acids at the 2- position are indicative of adulteration with an interesterified oil.

ECN42 (equivalent carbon number 42): The ECN42 is a test that measures the level of the triglyceride trilinolein and similar triglycerides. Trilinolein is a triglyceride that is abundant in oils such as sunflower, rapeseed, and grape seed but is virtually absent in olive oil.

Sterols: The total sterol content and measurement of individual sterols (cholesterol, brassicasterol, campesterol, stigmasterol, delta-7 stigmastenol, and beta- sitosterol) gives an indication of authenticity. Beta-sitosterol is present in particularly high levels relative to the other sterols in olive oil. High levels of brassicasterol indicate the presence of rapeseed oil, and high levels of delta-7-stigmastenol indicate the presence of sunflower oil.

Waxes and diols: Levels of waxes and diols—erythrodiol and uvaol—are much higher in solvent-extracted olive oil (olive-pomace oil or olive residue oil) than in other olive oils. Virgin olive oils, which are obtained by pressing the olive fruit, contain lower levels of these components than the cheaper olive-pomace oil.

Stigmastadienes: Some tests indicate whether the oil has been bleached during the refining process. Stigmastadienes are formed when the sterol components are exposed to the high temperatures of the refining process. Refining virgin olive oils is not permitted, so a relatively high level of stigmastadienes is a good indicator of the presence of cheaper refined oils.

Taste: Many would argue that the sensory characteristics of the oil are what matter most, but even the most sensitive palate cannot detect every case of adulteration. Taste testing does help indicate age, quality, and rancidity, however.

Fatty acid composition is a useful indicator of purity or the presence of oils other than olive oil. High levels of trans fatty acids can indicate the presence of refined olive oil or other refined vegetable oils in a virgin olive oil.

Three Testing Categories

The revised U.S. grade standards divide tests into three categories: mandatory, confirmatory, and optional. As might be expected, the mandatory tests will have to be performed on all lots of olive oil and olive-pomace oil. These tests will include flavor, odor, color, free fatty acid expressed as oleic acid, peroxide value, absorbency in UV, fatty acid composition, trans fatty acid content, desmethylsterol composition, total sterol, and stigmastadiene content.

There are, of course, many other tests one might wish to apply, such as pesticide residue testing and heavy metal content. And there are many other oils to which one might wish to apply the methods about to be required for olive oil. The market offers plenty of high-value oils that are equally vulnerable to adulteration, after all.

RSSL’s laboratory has investigated the suspected adulteration, or helped assess the authenticity, of expensive specialty oils such as evening primrose, starflower, walnut, almond, and wheat germ. In the absence of regulatory standards, determining authenticity is often a case of reaching a judgment based primarily on the profile of fatty acids, sterols, and tocopherols.

It would be naïve to suggest that the introduction of new regulations in the U.S. will put an end to olive oil adulteration. It does, however, bring the U.S. market into line with international standards and provides a set of definitions and standards against which olive oil and olive-pomace oil can be tested and marketed, and against which problem oils can be identified and rejected.

It may take some time for the analytical infrastructure to catch up with the requirements, however. Not every laboratory will be equipped to offer every test, and, perhaps more importantly, not every analyst will be experienced in providing a judgement when faced with results that may be within, or at the limits of, specification.

In the gray areas of deciding whether to accept or reject a suspect supply, a regulation and set of standards will never give a 100% guarantee of confidence that an oil is authentic or not, and the judgement of an experienced analyst is often more helpful than the raw data. Sometimes it is the combination of results that indicates a problem meriting further investigation, or a situation may occur in which explicable and understandable natural variation produces results at the margins of acceptability.

Griffiths is a technical specialist in lipids at RSSL in the United Kingdom; for more information, contact Karen Masters at or +44 (0)118 986 8541.


  1. University of the Free State. Successful conviction on edible oil adulteration. University of the Free State website. March 27, 2009. Available at: Accessed November 1, 2010.
  2. Riding A. Trial in Spain on toxic cooking oil ends in uproar. The New York Times website. May 21, 1989. Available at: Accessed November 1, 2010.



Current Issue

Current Issue

February/March 2015

Site Search

Site Navigation