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.