`Improved DNA Tracing Puts Olive Oil Adulterers on Notice - Olive Oil Times

Improved DNA Tracing Puts Olive Oil Adulterers on Notice

Apr. 22, 2013
Julie Butler

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By Julie Butler
Olive Oil Times Contributor | Reporting from Barcelona

Dr. Juan de Dios Alche and Dr. Fendri Mahdi

Spanish sci­en­tists claim they are close to offer­ing‭ pater­nity tests‭” ‬for vir­gin olive oil which would be a pow­er­ful ally against fraud.

Their advances in the art of DNA fin­ger­print­ing mean they now need‭ ‬only rel­a­tively small sam­ples‭ ‬-‭ ‬typ­i­cally‭ ‬100 – 200ml‭ ‬-‭ ‬to ver­ify if vir­gin olive oil is really of the vari­ety and ori­gin claimed.

And unlike chem­i­cal and sen­sory tests‭ ‬-‭ ‬the results of which can at most strongly indi­cate the oil has been cut with another veg­etable oil‭ ‬-‭ ‬find­ing the DNA of say hazel­nut or sun­flower oil in olive oil is‭ ‬unequiv­o­cal proof of its pres­ence,‭ ‬they say.

Dr.‭ ‬Juan de Dios Alché,‭ ‬lead researcher on the Spanish National Research Council‭ (‬CSIC‭) ‬project,‭ ‬told‭ ‬Olive Oil Times there is still much work to do but he hopes within six months the test will be com­mer­cially avail­able.

We‭’‬ve already had quite a few con­tacts from peo­ple in the food sec­tor,‭ ‬includ­ing in the United States,‭ ‬and believe there is a lot of demand for it,‭” he said.

Alché,‭ ‬from CSIC‭’‬s‭ ‬depart­ment of Biochemistry,‭ ‬Cell and Molecular Biology of Plants,‭ ‬part of the‭ ‬Estación Experimental del Zaidín insti­tute‭ ‬in Granada,‭ ‬also explained that it would‭ ‬sub­stan­tially‭ ‬com­ple­ment, but not replace, other ver­i­fi­ca­tion tests.

Olive Oil Times:‭ ‬What are the advan­tages of this test‭?

Dr.‭ ‬Juan de Dios Alché:‭ ‬Virgin olive oil is rel­a­tively expen­sive and peo­ple are will­ing to pay more for qual­i­ties they value,‭ ‬such as oil from a par­tic­u­lar region or vari­ety,‭ ‬some­thing dis­hon­est pro­duc­ers take advan­tage of.‭ ‬With this test we can ver­ify an olive oil‭’‬s authen­tic­ity,‭ ‬con­firm­ing whether it really is of the ori­gin and vari­ety, or vari­eties,‭ ‬stated on the label.

Q:‭ ‬What are its lim­i­ta­tions‭?

A:‭ ‬This is not a test that will deter­mine the grade of an olive oil.‭ ‬Also,‭ ‬it requires detec­tion of intact‭ ‬DNA,‭ ‬which is often hard to find in refined oil.‭ ‬That‭’‬s one of the rea­sons it‭’‬s designed to be used for vir­gin olive oil and should be seen as a com­ple­ment to other tests,‭ ‬not a replace­ment.

Also,‭ ‬in some cases we are unable to pos­i­tively ana­lyze sam­ples because they have‭ ‬very,‭ ‬very small amounts of DNA or because the DNA is degraded.‭ ‬In such cases we have to use larger sam­ples,‭ ‬some­times up to‭ ‬1‭ ‬liter.‭ ‬The use of high tem­per­a­tures dur­ing milling is one way in which DNA is degraded.

Q:‭ ‬How did you come to develop the test‭?

A:‭ ‬As part of our research on pollen we devel­oped a big data­base of DNA frag­ments taken from the leaves of more than‭ ‬90‭ ‬dif­fer­ent olive vari­eties,‭ ‬mainly from Spain,‭ ‬Portugal and Tunisia,‭ ‬but also with the most com­mon vari­eties from Italy,‭ ‬Greece,‭ ‬France,‭ ‬Morocco and Lebanon.

One of its uses is to cer­tify the olive vari­ety‭ ‬from olive pollen allergy vac­cines but we tried and found we could also use it to iden­tify olive oil,‭ ‬even though in Spain the whole olive fruit,‭ ‬includ­ing the seed,‭ ‬is crushed to make oil and we don‭’‬t know exactly where the DNA we find in it comes from.

Q:‭ ‬Your data­base is based on DNA from olive tree leaves yet sci­en­tists have reported find­ing the DNA in leaves from an olive tree did­n’t match that of the tree‭’‬s oil.

A.‭ ‬We have found that in the vast major­ity of cases they do coin­cide.

Q.‭ ‬How does the test work‭?

A:‭ ‬It‭’‬s based on the use of microsatel­lites‭ (‬also known as SSRs‭ ‬-‭ ‬Simple Sequence Repeats‭) ‬as mol­e­c­u­lar mark­ers.‭ ‬We extract‭ ‬DNA‭ ‬and use what‭’‬s known as poly­merase chain reac­tion‭ (‬PCR‭) ‬to amplify‭ ‬these SSR sequences. We‭ ‬then‭ ‬check their size by sequenc­ing and com­par­ing sizes with what’s already in our data­base.

Other mol­e­c­u­lar mark­ers now appear to pro­vide even higher res­o­lu­tion fin­ger­print­ing‭ ‬than SSRs‭ ‬but we still use microsatel­lites because there are already many data­bases based on them,‭ ‬such as ours,‭ ‬they are easy to inter­pret and repro­duce,‭ ‬and they have high dis­crim­i­na­tory power.

Q:‭ ‬Does the test take long and is the sam­ple pre-treat­ment com­pli­cated‭?

A:‭ ‬It cur­rently takes 7 – 10‭ ‬days, includ­ing analy­sis. We extract the DNA using a cen­trifuge,‭ ‬sol­vents and com­mer­cial kits we have cus­tomized,‭ ‬and use spe­cial­ized lab­o­ra­tory equip­ment for the test,‭ ‬espe­cially a PCR ther­mo­cy­cler and cap­il­lary sequencer.‭ ‬The nec­es­sary sam­ple pre-treat­ment is not that com­pli­cated, rel­a­tively speak­ing.

Q:‭ ‬What progress have you made in the last two years‭?

Apart from expand­ing the data­base,‭ ‬we‭’‬ve opti­mized the process of extract­ing DNA from oil sam­ples.‭ ‬We use var­i­ous meth­ods to extract the DNA,‭ ‬some of them com­mer­cially avail­able ones,‭ ‬but cus­tomized by us,‭ ‬and we‭’‬ve also opti­mized the ampli­fi­ca­tion process.

Q.‭ ‬Would this test be cost-effi­cient enough to be widely used‭?

A.‭ ‬The price is not deter­mined yet because we’re not mak­ing any com­mer­cial use of our method.‭ ‬But we have found there is‭ ‬demand for it from the food sec­tor and it‭’‬s pos­si­ble that in about six months we‭’‬ll be able to offer it as a ser­vice and yes,‭ ‬it would be afford­able.‭ ‬A small sam­ple can ver­ify a big batch of oil.

Q:‭ ‬What are you work­ing on now‭?

The test takes a long time so we‭’‬re try­ing to reduce that.‭ ‬We also plan to test a wider range of olive oil.

Furthermore,‭ ‬while we‭’‬ve been able to detect DNA from hazel­nut and sun­flower oils in olive oil,‭ ‬so far we can only con­firm the pres­ence of extra­ne­ous oils,‭ ‬we can‭’‬t quan­tify the pro­por­tion,‭ ‬so that‭’‬s some­thing we’re also work­ing on.

Further read­ing on mol­e­c­u­lar mark­ers and ver­i­fy­ing olive oil authen­tic­ity:

- Olive Oil Traceability, Olive Germplasm — The Olive Cultivation, Table Olive and Olive Oil Industry in Italy, Dr. Innocenzo Muzzalupo (Ed.)

- An Overview of the Authentication of Olive Tree and Oil

- Living in the 70’s – Detecting adul­ter­ation by seed oils, Richard Gawel


Technique devel­oped to detect poten­tial olive oil fraud. (Press release in Spanish from of the Spain’s National Research Council’s Zaidín Experimental Station.)
Fighting food fraud with sci­ence, Chemistry World
Olive Identification Gets Fast and Easy, Olive Oil Times


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