`Olive Oil Analysis Discussed at Annual Chemists' Meeting


Olive Oil Analysis Discussed at Annual Chemists' Meeting

May. 7, 2012
Alexandra Kicenik Devarenne

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Olive oil analy­sis received more than its fif­teen min­utes of fame at this year’s annual meet­ing of the Amer­i­can Oil Chemists’ Soci­ety (AOCS) 30 April to 2 May in Long Beach, Cal­i­for­nia. The week­end before the meet­ing there was a short course enti­tled Olive Oil Chem­istry and Sen­sory Rela­tion­ships, and Tues­day morn­ing fea­tured a tech­ni­cal group meet­ing and a ses­sion Olive and Spe­cialty Oil.”

Andy Proc­tor of the Uni­ver­sity of Arkansas intro­duced Rod Mailer of the Aus­tralian Oils Research Lab­o­ra­tory who started the olive oil short course with an overview of olive oil stan­dards around the world. Stan­dards have many ben­e­fits: they pro­vide mer­chants and con­sumers the assur­ance of authen­tic­ity, safety and fresh­ness, and they give pro­duc­ers a clear tar­get for pro­duc­tion.

But the cur­rent sit­u­a­tion is any­thing but clear, with a mix of stan­dards and meth­ods orig­i­nat­ing from both inter­na­tional bod­ies — such as Inter­na­tional Olive Coun­cil (IOC), Codex Ali­men­ta­r­ius and the Euro­pean Com­mit­tee for Stan­dard­iza­tion (CEN) — and from national gov­ern­ments moti­vated by dis­sat­is­fac­tion with the cur­rent envi­ron­ment. Mailer sug­gests Codex Ali­men­ta­r­ius, a pro­gram charged both with pro­tect­ing con­sumer health and pro­mot­ing fair trade prac­tices, as the log­i­cal body to set inter­na­tional stan­dards for olive oil.

Angela Sheri­dan of the Cana­dian Food Inspec­tion Agency (CFIA) gave a pre­sen­ta­tion about the work being done in Canada to inspect olive oil. In the ser­vice of their man­date to pro­tect con­sumers against prod­uct mis­rep­re­sen­ta­tion and fraud, the CFIA con­ducts tar­geted sam­pling and analy­sis of olive oils using the IOC stan­dards. The pro­gram is con­cerned pri­mar­ily with adul­ter­ation. The per­cent­age of sam­ples judged unsat­is­fac­tory has ranged from 47 per­cent in 2006 – 7 to 11 per­cent in 2009-10. It was an encour­ag­ing story, show­ing what hap­pens when a gov­ern­ment is will­ing to cre­ate a focused pro­gram and allo­cate fund­ing to the objec­tive.

One of the recur­ring themes of the stan­dards dis­cus­sion was the prob­lem of chem­i­cal pro­files that are based on a par­tic­u­lar region. The pro­file of an olive oil will vary tremen­dously depend­ing on the olive vari­ety used and the cli­mate where the olives are grown. A clas­sic exam­ple of this is are the campes­terol and Δ7 stig­mas­tenol lev­els of Israeli oils made from the Barnea vari­ety. These oils will reg­u­larly fall out­side the IOC lim­its for those fatty acids and sterols.


Such nat­ural vari­a­tion in olive oil has led to some of these lev­els being set dif­fer­ently in national stan­dards; the campes­terol limit is ≤ 4.5 in the USDA stan­dard, for exam­ple, instead of the ≤ 4.0 of the IOC stan­dard. Mailer points out that the vari­abil­ity of the chem­i­cal pro­file of olive oil from places like Aus­tralia can be huge, since their olive grow­ing region extends from the trop­i­cal to the cool tem­per­ate.

Whereas the sterols and fatty acid pro­file of an olive oil are exam­ined to assure authen­tic­ity, other tests are aimed at assess­ing qual­ity and fresh­ness. The free fatty acid level, per­ox­ide value and UV absorbency are the tra­di­tional tests used for this pur­pose. Dur­ing the short course there was exten­sive dis­cus­sion of two other tests that have been in use in the North­ern Euro­pean olive oil trade since at least 2006 and are incor­po­rated into the recently adopted Aus­tralian stan­dard for olive oil: pyropheo­phytin (PPP) and dia­cyl­glyc­erols (DAGs).

Sup­port for the use of PPP and DAGs as indi­ca­tors of olive oil age and qual­ity was pre­sented by Clau­dia Guil­laume of the Mod­ern Olives lab­o­ra­tory in Aus­tralia in the form of find­ings from three years of research on olive oil stor­age and qual­ity assess­ment.

The PPP test mea­sures degra­da­tion prod­ucts of chloro­phyll in olive oil. This degra­da­tion of chloro­phylls to pyropheo­phytin was found to take place at a pre­dictable pace mak­ing it pos­si­ble to gain infor­ma­tion about the age of an olive oil. The rate at which the degra­da­tion occurs can be accel­er­ated by even short peri­ods at high tem­per­a­tures — such as those present dur­ing the deodor­iz­ing or soft col­umn refin­ing process — mak­ing it a use­ful indi­ca­tor of the pres­ence of deodor­ized olive oil as well as of the age of an oil.

The DAGs test mea­sures the pro­por­tion of two forms of dia­cyl­glyc­erol: 1,2 and 1,3. In oil freshly made from sound, good qual­ity olives, the preva­lent form of DAG is the 1,2 form, where the fatty acids are bonded to a glyc­erol mol­e­cule in the 1 and 2 posi­tions. The bond on the 2 posi­tion is weak and eas­ily bro­ken, lead­ing to the migra­tion of that 2 posi­tion fatty acid to the 3 posi­tion. This results in the much more sta­ble 1,3 DAG. This makes the ratio of 1,2 DAGs to the total DAGs a good indi­ca­tor of the qual­ity of the olive fruit and the pro­cess­ing. It is also an indi­ca­tor of the age of an oil, since the migra­tion from 1,2 to 1,3 DAGs takes place nat­u­rally as oil ages. Warmer stor­age tem­per­a­tures and higher free fatty acid lev­els will both accel­er­ate this process, but DAGs are not affected by the short expo­sure to high heat that is char­ac­ter­is­tic of deodor­iz­ing.

The exper­i­ment looked at the aging process in olive oils from many dif­fer­ent cul­ti­vars stored in dif­fer­ent light and tem­per­a­ture con­di­tions. Oil was stored in dark and clear glass, and at 20 and 30º C (68 and 86º F). Guil­laume showed data indi­cat­ing the pre­dictable decline of DAGs by 20 – 25 per­cent and the increase of PPP by 6 – 8 per­cent per year under nor­mal stor­age con­di­tions. Clear glass or warmer tem­per­a­tures accel­er­ated the rate of degra­da­tion in the dif­fer­ent para­me­ters. Olive vari­ety was found to have no bear­ing on the DAGs and PPP. The qual­ity of the oil at the out­set did have an effect on the DAGs, but not on the PPP.

The detec­tion of deodor­ized oil, some­thing that is prob­lem­atic with the test­ing called out in the cur­rent USDA and IOC stan­dards, is aided by ana­lyz­ing the results of sev­eral tests includ­ing the DAGs and PPP. The pro­gres­sion of the nat­ural aging of vir­gin olive oil is well under­stood and doc­u­mented. The red flag for the pres­ence of deodor­ized oil goes up when the dif­fer­ent chem­i­cal para­me­ters don’t add up. For exam­ple, if the PPP is high and the other indi­ca­tors are not, then the high heat of soft col­umn refin­ing can be the cause. To inves­ti­gate these effects, the Mod­ern Olives team cre­ated deodor­ized oil in the lab and ana­lyzed it.

Research pre­sented dur­ing the reg­u­lar ses­sion Tues­day by Dag­mer Behmer of Bruker Optics, done in col­lab­o­ra­tion with Chris­t­ian Gertz of the Offi­cial Insti­tute of Chem­i­cal Analy­ses in Ger­many, con­firmed the Mod­ern Olive find­ings. PPP increased and DAGs decreased in an almost lin­ear fash­ion. Their find­ings also backed up the cor­re­la­tion found with sen­sory analy­sis by the researchers at UC Davis. Behmer’s pre­sen­ta­tion had another tan­ta­liz­ing aspect: the analy­sis of PPP and DAGs using near infrared spec­troscopy (FT-NIR). With this tech­nol­ogy, a sam­ple can be ana­lyzed in 30 sec­onds, and the accu­racy is not depen­dent on a highly skilled oper­a­tor.

A sig­nif­i­cant find­ing of the Mod­ern Olives research was born out by the research done by the Uni­ver­sity of Cal­i­for­nia Davis Olive Cen­ter: there was a direct cor­re­la­tion between sen­sory find­ings and PPP and DAGs. In a sum­mary of two reports from UCDOC, research direc­tor Selina Wang showed data that indi­cated that falling out­side the lim­its for PPP and DAGs — UCDOC used the lim­its from the Aus­tralian stan­dard — was the most indica­tive of fla­vor defects in the super­mar­ket oils they tested. Wang con­cluded her pre­sen­ta­tion with the call for faster, bet­ter and cheaper test­ing meth­ods for olive oil authen­tic­ity and qual­ity.

Faster, bet­ter and cheaper were cer­tainly in everyone’s mind dur­ing the panel mod­er­ated by Richard Cantrill, AOCS Tech­ni­cal Direc­tor, focus­ing on the poten­tial of new instru­men­tal approaches for olive oil analy­sis. Jack Cap­pozzo of the Insti­tute for Food Safety and Health, Hui Li of Bruker Optics, Carol Schnei­der of Alpha MOS and Stephan Bau­mann of Agi­lent talked about an array of ana­lyt­i­cal pos­si­bil­i­ties using near infrared spec­troscopy, tan­dem mass spec­trom­e­try, gas chro­matog­ra­phy and other tech­nolo­gies includ­ing soft­ware for ana­lyz­ing the data. These new tech­niques hold the promise of a reduc­tion of reliance on wet lab” tech­niques that are time con­sum­ing, and some­times demand­ing and expen­sive to per­form. Lab­o­ra­tory analy­sis of the volatile com­pounds in olive oil is of par­tic­u­lar rel­e­vance to the inter­sec­tion of sen­sory and chem­istry.

The worlds of sen­sory and chem­i­cal analy­sis came together in an olive oil tast­ing by CalA­thena, a Cal­i­for­nia olive oil con­sult­ing and edu­ca­tion com­pany. The group blind tasted four oils, then dis­cussed the sen­sory attrib­utes of each oil, fol­lowed by a look at the oil’s chem­i­cal analy­sis. Only after all four oils had been dis­cussed in this way were the iden­ti­ties of the oils revealed. All were of the cul­ti­var Picual, but of vary­ing ages and ori­gins. A very ran­cid super­mar­ket oil — which bore a Best By” date of August 2013 — had a PPP of 36.2 (well above the Aus­tralian stan­dard limit of 17) and DAGs of 30.5 (below the limit of 35). The free fatty acids, per­ox­ide value and UV absorbency were within the IOC lim­its, but it would clearly have failed sen­sory analy­sis. The PPP of an Aus­tralian Picual from April 2011 was 3.4 and an Aus­tralian Picual from April 2012 was less than 1. The good-tast­ing oils all had DAGs above 88. This tast­ing both demon­strated the cor­re­la­tion between chem­istry and fla­vor, and gave some of the class par­tic­i­pants their first taste of real, fresh extra vir­gin olive oil.

A pre­sen­ta­tion by Ramon Apari­cio of the Insti­tuto de la Grasa in Spain talked about the reli­a­bil­ity of sen­sory analy­sis. Pref­ac­ing his pre­sen­ta­tion with a state­ment say­ing he sup­ports the sen­sory com­po­nent of the olive oil stan­dard, Apari­cio gave an exam­ple of objec­tive and sub­jec­tive views of real­ity using two paint­ings, one real­is­tic and one abstract. His pre­sen­ta­tion enu­mer­ated the many pos­si­ble influ­ences on a human taster, sug­gest­ing that chem­i­cal mark­ers of defects, once the thresh­olds have been estab­lished, would be more reli­able than sen­sory analy­sis.

He also pre­sented an inter­pre­ta­tion of PPP and DAGs research say­ing that the dif­fer­ent results obtained from olive oils stored under dif­fer­ent con­di­tions or made from olives of dif­fer­ing qual­ity made the tests unre­li­able. He argued that that one could not estab­lish causal­ity in the case of those tests.

A pre­sen­ta­tion on sen­sory analy­sis and the brain by Diego Gar­cia Gon­za­lez of Insti­tuto de la Grasa also looked at the chem­i­cal com­po­nents and influ­enc­ing fac­tors asso­ci­ated with sen­sory attrib­utes in olive oil. Olfac­tion is char­ac­ter­ized as a highly emo­tional sense. For exam­ple, neo­pho­bia, the aver­sion to the new, is an impor­tant influ­encer of reac­tions to odors. In sen­sory cir­cles, it seems that famil­iar­ity breeds lik­ing rather than con­tempt.

This overview of olfac­tion was a pre­am­ble to the cen­tral topic of the research: how the brain per­ceives aro­mas. Using func­tional mag­netic res­o­nance imag­ing (fMRI), researchers mapped the areas of the brains of habit­ual olive oil con­sumers, show­ing activ­ity in response to dif­fer­ent olive oil aro­mas both pleas­ant and unpleas­ant. Gar­cia sug­gests areas of research for the future that include new approaches for select­ing and train­ing sen­sory pan­elists as well as the olfac­tory assess­ment of volatile mark­ers to estab­lish their sig­nif­i­cance and con­tri­bu­tion to aro­mas.

This area, the char­ac­ter­i­za­tion of key aroma com­pounds was the topic of research pre­sented dur­ing a reg­u­lar meet­ing ses­sion by Michael Granvogl of the Tech­ni­cal Uni­ver­sity of Munich. This was not research on olive oil, but on Styr­ian pump­kin seed oil. This oil car­ries a pro­tected des­ig­na­tion of ori­gin, and is a highly regarded spe­cialty prod­uct from the region of Styria (south east­ern Aus­tria). The researchers sep­a­rated and iden­ti­fied the many volatile com­pounds that char­ac­ter­ize the odor of the oil and then recre­ated that aroma. This was a com­plex task since the con­cen­tra­tion of a com­pound does not cor­re­late directly with its sig­nif­i­cance in an aroma. They ana­lyzed the odor activ­ity value (OAV) by tak­ing into account both the con­cen­tra­tion of the com­pounds and their per­cep­tion thresh­olds. Their recre­ation of the toasty nutty aroma of Sty­gian pump­kin seed oil in a neu­tral oil base was aston­ish­ing, and of great rel­e­vance for olive oil qual­ity analy­sis.

A panel dis­cus­sion on PPP, DAGs, UV and the life of oils mod­er­ated by Cather­ine Watkins, Asso­ciate Edi­tor of AOCS inform mag­a­zine, began with the dec­la­ra­tion, I am the most impor­tant per­son in the room; I rep­re­sent the con­sumer.” The panel dis­cus­sion cen­tered on the value of these ana­lyt­ics for qual­ity assur­ance in the mar­ket. There was agree­ment among almost every­one on the panel that PPP, DAGs and UV are the best tools avail­able right now, and that the tech­nol­ogy is con­tin­u­ally evolv­ing to give us new, bet­ter meth­ods of analy­sis. Another point of agree­ment was that no sin­gle test gives the entire story and the results must be ana­lyzed together. Gar­cia made the state­ment that we should be care­ful not to con­fuse con­sumers with talk about fresh­ness and qual­ity, which are sep­a­rate issues. Paul Miller of the Aus­tralian Olive Asso­ci­a­tion (AOA), speak­ing from the audi­ence, said that in the AOA’s out­reach con­sumers embraced the con­cept of fresh” with­out any prob­lem. He also made the point that in all of the dis­cus­sion of stan­dards we must be clear about the fact that these are min­i­mum stan­dards that describe an oil at the end of its life.

Reg­u­la­tory con­sid­er­a­tions were the topic of a panel mod­er­ated by Miller. That panel included two new speak­ers: Mer­cedes Fer­nan­dez of IOC and Tom Mueller, inves­tiga­tive jour­nal­ist and author of Extra Vir­gin­ity: The Sub­lime and Scan­dalous World of Olive Oil. Fer­nan­dez gave a his­tory of the IOC and out­lined some of its activ­i­ties. Mueller used his intro­duc­tory time to point out some of the ten­sions that exist in the olive oil world, such as the dif­fer­ence between stan­dards that are designed to pro­tect con­sumers and those that focus on free trade. Another is the bal­anc­ing act between national pride and nation­al­ism. He also decried the lack of action since the Jan­u­ary 2012 Cal­i­for­nia sen­ate sub­com­mit­tee hear­ing that enu­mer­ated obvi­ous, total fraud.

The final panel of the short course Where do we go from here?” was mod­er­ated by Dan Flynn of UC Davis Olive Cen­ter and included Ed Frankel of UC Davis. The irrel­e­vance of stan­dards with­out enforce­ment was agreed upon. Sheri­dan of the CFIA summed it up: a ded­i­cated pro­gram with allo­cated resources works. Guil­laume of Mod­ern Olives spoke up for con­sumers: they should get what they are pay­ing for, with truth-in-label­ing and a fresh, qual­ity prod­uct. There was gen­eral agree­ment that there is lot of promise in new instru­men­ta­tion and soft­ware to pro­vide excel­lent ana­lyt­i­cal tools for assess­ing olive oil qual­ity and purity, but that it is an emerg­ing field. Guil­laume made the com­ment that where we stand now, sen­sory pan­els are prob­a­bly more prac­ti­cal in most cases. Gar­cia con­tributed that the def­i­n­i­tion of food safety in Europe now includes authen­ti­ca­tion.

In addi­tion to the olive oil short course and reg­u­lar ses­sions at the AOCS meet­ing, there were meet­ings related to olive oil and the usual net­work­ing and trade show activ­i­ties. The high level of inter­est this year is an encour­ag­ing sign that the issue of olive oil qual­ity is a hot topic among the world’s top oil chemists and equip­ment man­u­fac­tur­ers.

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