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
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
- Determination of the fatty acid composition
- Trans-fatty acid
- Desmethylsterol composition (% total
- Total sterol content
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
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.
University of California at Davis. Tests
indicate that imported “extra virgin” olive
oil often fails international and USDA
standards; Jul 2010.
- International Olive Council, Market Commentary;
- North American Olive Oil Association;
Chairman’s Report; Jan 2010.
- Kyriakidis, N.; Skarkalis, P. J. AOAC Int.
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: email@example.com. A copy of the new USDA standards
can be found at www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELDEV3011889.