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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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