This weeks pick of Extra virgin olive oil researchadmin | July 2, 2011
I try to find the time to scoure the published literature on extra virgin olive oil research each week. Mostly I find that the quality or practical relevance of the research doesn’t warrant a review but this week saw a raft of exciting stuff from a wide range of olive related fields – marketing, packaging, fraud identification and health. So here they are in a longer format and a little more commentary and explanation than usual. – RG
207 Ontario consumers were asked how much extra they would hypothetically be willing to pay for extra virgin olive oil based on 1) its country of origin, 2) whether the oil was from a geographically defined area (GI), 3) whether the oil was from a Protected Designation of Origin (PDO), and a number of other factors including its organic status. Over 80% of consumers were willing to pay a significant premium ($CAN 7.68-$9.48 per litre) for oils of Italian origin over Spanish or Greek oils (which were not preferred over each other). Over ¾ of respondents preferred organic oils and said they were willing to pay around $CAN8 extra per litre for them – more than that for oils from a geographically defined area. The colour of the oil, and the colour of the glass packaging (clear vs other) did not significantly affect the amount they were willing to pay. Interestingly, while consumers were willing to pay more for GI oils, most of the premium was captured by the country of origin. Lastly, preferences were greatly affected by shopping location. Gourmet food shoppers were willing to pay more for Italian over organic while supermarket and farmers market patrons were the opposite. The preference for Italian over other countries of origin was consistently higher regardless of shopping location.
Menapace et al. (2011) Consumers’ preferences for geographical origin labels: evidence from the Canadian olive oil market. European Review of Agricultural Economics Vol 38 (2) (2011) pp. 193–212. doi:10.1093/erae/jbq051
Comment: The authors discuss the well known phenomenon that a persons’ stated willingness to pay is usually a gross overestimation of how much they actually do pay when forking out their hard earned cash. So the $ figures stated should be taken with a grain of salt. However the results probably explain why so much extra virgin olive oil from around the Mediterranean is passed off (either explicitly or implicitly) as Italian. Those Italian looking labels and Italian sounding brand names that are actually filled with Spanish Picual have a lot to answer for.
This paper reviews the use of genetic markers that remain in edible oils after processing for authentication purposes. Earlier genetic technologies required that either a large quantity of oil needed to be analysed or that the oil contained a reasonable amount of water soluble material before a sufficient quantity of DNA could be extracted. These issues seem to have been largely resolved with less than 1ml of clean oil now required. While the paper mainly focussed on the more difficult task of distinguishing varietal composition for the purposes of validating PDO status (relevant to about 1 millionth of the total value of the EVOO sector worldwide), it touched on the fact that many genetic markers specific to both olives and other seed crops used to adulterate olive oil have been determined, and these could be used to authenticate extra virgin olive oil.
Agrimonti et al. (2011) The use of food genomics to ensure the traceability of olive oil. Trends in Food Science & Technology, 237-244. doi:10.1016/j.tifs.2011.02.002
Comment: Remember when law enforcement used fairly subjective forms of evidence to prove guilt. Then along came DNA testing. Everything changed. The raft of expensive chemical tests with arbitrary limits currently used to identify adulteration could be made redundant overnight by a good genomic test. It would put an end to arguments about whether a 4% level of campesterol is too high or too low depending on what part of the world you come from or what varieties you grow. If the oil contains genetic material from a plant other than olive then end of story. Convicted as charged!! Testing is about clarity, and ensuring those that adulterate get caught, and (equally importantly) those who’s legitimately made olive oils fall outside some arbitrary limit aren’t forced to label them as worthless fruit oil.
One volume on Nitrogen gas was pumped through extra virgin olive immediately after decanting and just prior to bottling. This sparging decreased dissolved oxygen in the bottled oil by 55% which resulted in a 1.6meq/kg reduction in peroxide value. Sparged oils contained 10% fewer total flavour volatiles (as expected), but actual sensory differences were not observed.
Masella et al. (2010) Nitrogen stripping to remove dissolved oxygen from extra virgin olive oil. Eur. J. Lipid Sci. Technol. 112, 1389-1392. Doi: 10.1002/ejlt.200900277
Comment: Many EVOO producers believe that their job is done once the oil is sitting in tank. Winemakers have long known that their wine is only as good as how carefully it was bottled (particularly with regard to dissolved oxygen and headspace oxygen), and the stopper that holds it. Lots more work needs to be done on bottling conditions for EVOO so as to extend the period of freshness following bottling. High polyphenols/antioxidants in EVOO are not a universal panacea for long shelf life. I’ve seen lots of high polyphenol oils that are simultaneously bitter/peppery and horribly rancid. One can only assume that they have been let down by either poor storage conditions, by having high dissolved/total oxygen at bottling, or by packaging that has a high oxygen transfer rate. We all know the appropriate conditions for EVOO storage, but the latter two influences on EVOO shelf life are largely unexplored. This paper is a good start, but optimal sparging conditions for EVOO are yet to be determined.
Firstly some background to the next paper. It is widely believed that the polyphenols in extra virgin olive oil play a major role in its healthfulness. However, a number of studies have found that many of the complex, uniquely EVOO polyphenols are either broken down during digestion into smaller rather unexciting phenolics (that you find in hundreds of everyday foods and beverages), or they do not seem to be absorbed at all. This cracker of a paper takes a close look at this and comes up with some surprising results.
The two most abundant phenolics in EVOO were shown to be resistant to breakdown by stomach acids but were chemically altered to a significant extent after they passed through a segment of intestinal wall. Specifically, the original phenolics were enzymatically reduced (the opposite of oxidised), which allowed them to be subsequently bonded to a specific type of sugar called a glucuronide.
Pinto et al. (2011) Absorption and metabolism of olive oil secoiridoids in the small intestine. British Journal of Nutrition. 105, 1607-1618. Doi: 10.1017/S000711451000526X
Comment: So what does this mean? Well to date, researchers have used specific phenolics in either blood plasma or in urine as markers of the ability of humans to absorb EVOO polyphenols. From this work it appears that they may have been looking for the wrong ones! Most analytical methods are highly specific in their scope, so if you are looking for the wrong thing, then you are most likely not to find anything. In the words of the authors “it seems reasonable that previous human studies aimed at investigating the pharmacokinetics of olive oil secoiridoids (aka polyhenols) may have underestimated the full extent of the absorption” (p 1616).