This is the second of a short series aimed at explaining the whys, the how and the what (and the what-nots) of analyses that are commonly applied to extra virgin olive oil.

Analysis Name: Total polyphenols

What does it measure?: The combined pool of compounds in olive oil that are in the phenolic chemical group (containing six carbon atoms attached to each other in a ring like formation with one or more oxygen+hydrogen groups attached to the ring). An example of a common olive oil polyphenol is shown in Figure 1.  In laymans terms, ‘total polyphenols’ are a measure of the combined total of the most important group of antioxidants in extra virgin olive oil.

Figure 1: Hydroxytyrosol – An example of a phenolic compound found in extra virgin olive oil.

Does the polyphenol level affect extra virgin olive oil status?: No. Many perfectly grown and made olive oils have low or medium polyphenol levels.

How it works: The polyphenols are extracted from the oil into a water/alcohol mix. A reagent is added which reacts with the polyphenols turning it blue/green. The depth of the blue/green colour is measured, and is directly proportional to the amount of polyphenols in the sample.

Is it a measure of quality?: Depends. Quality is a term that encompasses the general concept of ‘fitness for use’. So if you are ‘I want to live forever’ type of person then yes higher polyphenols which are of the antioxidant family could be perceived to be of higher quality in your eyes.  But conversely if you want to use extra virgin olive oil to make great tasting grilled potato slices on the BBQ for your hungry kids that don’t taste bitter, then a high polyphenol oil (by a consistently applied ‘fitness for use’ criterion), is of lower quality.

Analysis debuted: 1958. Initially developed for wine polyphenol analysis,  It was officially adopted in a modified (but in an incompetely described form) for olive oil by the International Olive Council in 2005.

Unit of Measurement: milligrams/kilogram of oil (1mg=1/1,000 of a gram).

Range in Extra Virgin Olive Oil: 80-2,000 mg/kg (measured as caffeic acid equivalents). Common range 200-400 mg/kg.

Accuracy of method: The first step of the analysis involves extracting the polyphenols out of the oil using a solvent. This step, depending on how carefully it is done, can cause variable end results in the order of +/- 10%. For this reason, it is necessary to repeat the test and take an average.

Use by olive oil producers: Unknown. Probably more so by New World olive producers.

Degree of difficulty: By automated lab standards the method is time and labour intensive, and therefore relatively expensive.

Practical effects of high readings of polyphenols

–  Typically more bitter and/or pungent (peppery).

–  Greater health benefits.

–  Assists in prolonging shelf life.

–  Potential for slightly higher smoke point.

Polyphenol level in extra virgin olive oil is affected by:

Cultivar – some varieties of olives tend to produce naturally higher polyphenol levels than others. For example, the average polyphenol levels in oils made from the cultivar ‘Coratina’ are significantly higher than those made from the cultivar ‘Arbequina’.

Olive maturity at harvest – The greener the olives used to make the oil, the higher the polyphenol levels.

Climate – Cool climates tend to favour higher polyphenol levels.

Tree water status – Excessive water availability reduces polyphenol levels.

Enzymes – The use of enzymes as a processing aid increases polyphenol levels

Water use during processing – Adding water to olive paste before extraction (e.g. 3 phase processing) reduces polyphenol levels.

Post harvest – Delays between harvest and processing reduce polyphenol levels.

Disease/Fruit quality – Incidence of fungal disease, olive fly attack and frost damage decreases polyphenol levels.

Age of the oil – Polyphenols levels decline as the oil ages.

Other comments:

The method only measures the size of the entire pool of the hundreds of polyphenol types that exist in extra virgin olive oil. Information about the amount of a specific polyphenol can only be achieved using highly sophisticated methods called high performance liquid chromatography or HPLC.

The relatively high cost of conducting the official method has led to an alternative rapid method to be developed. Called NIR or Near Infrared Spectroscopy, it is a method that can almost instantly estimate the polyphenol reading from a drop of oil, and it costs around 1/5 that of the official method. However it has its limitations, and its accuracy is laboratory dependent. Something for another blog post.

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I often get asked whether extra virgin olive oil is more fattening than other edible oils. Given the frequency that the question is posed, I’ll assume that there is some ‘information’ out there somewhere saying that it must be so. Or perhaps it is just a case of people thinking that if extra virgin olive oil is so healthy for you then it must have some downside. Can’t have your cake and eat it too right?

So I searched the peer-reviewed scientific literature to find out the energy (or calorific) values of different edible oils. Two papers provided some relevant data.

Fassinou et al. (2010) measured the energy values for a wide range of edible oils (Figure 1), but unfortunately olive oil was not one of them. However I’ve provided a logical estimate of the energy value of extra virgin olive oil based on the predictive model that they derived (1).

Figure 1: Energy values of various edible oils. Value for extra virgin olive oil is an estimate. See footnote 1.

Sadrameli et al. (2008) determined the energy values of the free fatty acids themselves (actual edible oils comprise 3 fatty acids of various sorts joined together to a glycerol molecule, not as individual free fatty acids). However, these values can presumably be good proxies of the energy values of the edible oils that are rich in a particular fatty acid (oleic acid makes up on average ¾ of the fatty acids in olive oil for example) (Figure 2). However as all edible fats comprise a mixture of fatty acids combined in various combinations in groups of three, this data is at best an estimate of the energy values of real edible oils.

Figure 2: Energy values of different fatty acids. Examples of edible fats that have high proportions of that fatty acid are given in parenthesis.

So what’s the conclusion? There is no practical difference in the energy values of the different edible oils.

OK, these results do not consider that our bodies may absorb one type of fat differently from another. Some have suggested that we absorb short chain fatty acids such as those found in coconut oil differently. You can read more about the good, the bad and the ugly of this possibility elsewhere in this blog (search for coconut oil in the search box to the right), but based purely on the maximum potential of each fat to contribute to our daily energy intake, there is little evidence of any practical differences between edible oils when it comes to their energy quotient (2).

References

Fassinou, W.F., Sako, A., Fofana, A., Koua, K.B. and Toure, S. (2010) Fatty acids composition as a means to estimate the high heating value (HHV) of vegetable oils and biodiesel fuels. Energy, 35, 4949-4954. doi:10.1016/j.energy.2010.08.030

Sadrameli, S.M., Seames, W. and Mann, M. (2008) Prediction of higher heating values for saturated fatty acids from their physical properties. Fuel, 87, 1776-1780. doi:10.1016/j.fuel.2007.10.020

Footnotes:

(1) The energy value can be predicted from the ‘carbon number’ of the oil. The carbon number is the average carbon chain length of the fatty acids that comprise the oil. In olive oil the carbon number averages 17.5 (based on the fatty acid profiles of 500+ extra virgin olive oils reported by Mailer and Ayrton 2008). The energy value of the ‘typical’ extra virgin olive was then estimated using the predictive model derived by Fassinou et al. (2010)..

(2) To save you scrambling for your abacuses paleo people, coconut oil has on average 3% lower energy value compared with the other oils, which is due to the lower average carbon number of the predominant fatty acids in coconut oil. 3% less energy but 90% less antioxidants. Take your pick.

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For once I have a theme!

But first, I must rid myself of a burden. There are no polyphenols in extra virgin olive oil. I’ve been resisting saying so for years, but now I must now confess. There is nothing poly(merised) about them. Yes, a couple of them could be a bit binary (depending on how you define it), but poly, errr no. Yes, many have a few optional extras like having attached sugars and esters hanging off them, which most certainly gives them interesting biological and health giving properties, but they are generally comprised of single simple phenolic monomers. They remind me of those troglodytes creatures that ruled the world during the Cambrian Period. There were thousands of different types – all very intricate and ecologically specialised, but in the general scheme of things, they were relatively biologically simple critters. Now I’m rid of the weight of this chemo-trivia, here are a few interesting, and practical research results about the phenolics in EVOO.

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The researchers compared the ability of total phenolics and absorbance at 255nm (K255) to predict the perceived bitterness of EVOO’s. The 35 oils from 4 Italian varieties ranged in bitterness from 1 to 7 on the International Olive Council rating scale which corresponded total phenolics of around 200 to 650 mg/L, and to 0.05 to 0.65 in K255. Total phenolics were found to be a poorer predictor of perceived bitterness (correlation 0.69) compared with the almost perfect, K255 (correlation of 0.98). The bitterness of these oils could be predicted by multiplying the K255 measure by 14 and subtracting 0.6

Comment: The K255 index for bitterness was first proposed in 1992 and has been used quite widely by the international industry. Compared to total phenolics, K255 is a very easy and quick and accurate analysis. I’m not sure that the paper broke any new ground except that it provided a link between the K255 measure and bitterness ratings using the IOC rating scale. But of course the relationship given above is wholly dependent on the panel that provided the ratings. While bitterness is one the attributes on the official IOC rating sheet, to the best of my knowledge, unlike the defects, cross panel comparisons for bitterness is not conducted. Well it wasn’t done when I was a panel leader anyway. Regardless of panel differences, K255 still seems to be a good predictor of relative bitterness amongst samples.

The relatively poor relationship between bitterness and total phenolics was unexpected. I have seen other data sets where the correlation was much stronger than reported here. Interestingly, the method used to determine total phenolics was not given which was a major oversight given that the method of extraction of phenolics from the oil plays a crucial role in the outcome. The method is also notoriously subject to variable results (where a 10% error is accepted by those who do them), so doing triplicate or more replications would be needed to ensure that the poor relationship between total phenol measures and bitterness wasn’t due to measurement error.

Faviti et al. (2013) Extra virgin olive oil bitterness evaluation by sensory and chemical analyses. To appear in: Food Chemistry DOI: http://dx.doi.org/10.1016/j.foodchem.2013.01.098

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Crushing between 1 and 10% leaves with ripe olives resulted in oils with higher free fatty acidity, peroxide value and K232 (measures of primary and secondary oxidation respectively). Adding leaves produced oils with higher chlorophyll aka they were greener. Adding over 5% leaves also increased oxidative stability and tocopherol content.

Comment: Lab scale work. Phenolics were not measured which seemed to be an oversight given that both tocopherols and phenolics contribute to oxidative stability. Also personally, I’d like to think that the oil I buy is made from olive fruit rather than leaves. Call me old fashioned.

Malheiro et al. (2013) Effect of olive leaves addition during the extraction process of overmature fruits on olive oil quality. Food Bioprocessing Technology,6, 509–521.

DOI: http://dx.doi.org 10.1007/s11947-011-0719-z

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Malaxing for 40 minutes at 35C caused a 25% increase in both total phenolics and the pungent phenolic oleocanthal compared with malaxing at 25C (Figure 1), which could be explained by a 50% reduction of the activity of the major enzyme (polyphenol oxidase,  PPO) responsible for oxidative losses of phenolics at the higher temperature. The longer malaxation time, the lower the total phenolics.

Figure 1: Concentrations (mg/kg) of oleocanthal and total phenolics as a function of malaxation temperature (malaxation time = 40 minutes).

Comment: Mill scale work (yay!). The fact that high temperatures can knock out PPO probably also explains why dipping olives into hot water prior to processing results in oils with higher phenolics.

Bitchy comment: If you believe that EVOO is just a polyphenol dietary supplement (rather than a tasty food), then these results suggest that you should insist on HOT pressed olive oils.

Taticchi et al. (2013) The influence of the malaxation temperature on the activity of polyphenol-oxidase and peroxidase and on the phenolic composition of virgin olive oil. Food Chemistry, 136, 975–983.

http://dx.doi.org/10.1016/j.foodchem.2012.08.071

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12 Spanish people were fed a diet that was devoid of polyphenols except for an olive oil fortified with olive oil phenolics i.e.  +250, 500 and 750mg/L. Blood plasma content of the key phenolic substances that had passed from the digestive system increased substantially when the subjects ate the oils with +500mg/L phenolics. Eating oils with +750 mg/L phenolics did not increase blood plasma phenolics over the +500mg/L diet. The authors appeared to recognise that phenolics impact on the taste and therefore the acceptability of EVOO. They stated that “The sensory acceptance is the principal barrier for the acceptance of a functional food”. In the case of EVOO high phenolics relates to high bitterness and/or pepperyness. So they also determined the taste acceptability of the oils with added phenolics. As phenolic content went up, acceptance by the tasters declined. The authors felt that the olive oil with a content of 500 mg/kg of phenolics provided “a good pharmacokinetic response and a good sensory acceptability” (in laymans terms, a good compromise between being healthy and not being overly bitter). The olive oil with 500mg/L was rated on average somewhere between “I like it a bit” and “I neither like nor dislike”. They went on to say that” Moreover, by consuming 30 ml of M-EVOO (+500mg/L) it is easy to reach the 5 mg daily dose of hydroxytyrosol and derivates recommended by the EFSA Panel”

Comment: The authors should be congratulated for recognising that long term consumption of a healthy food is only assured if it has an acceptable taste. EVOO included. But why not consume 60gms of something you really like, rather than 30 gms of something that you only like a bit?

Rubio et al. (2012) Impact of olive oil phenolic concentration on human plasmatic phenolic metabolites. Food Chemistry, 135, 2922–2929.

http://dx.doi.org/10.1016/j.foodchem.2012.07.085

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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

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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.

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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.

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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.

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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).

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There have been many claims made as to the health benefits of extra virgin olive oil – While a few are well reasoned, many are over the top. Statements like “this study proves that EVOO consumption cures this cancer or that cancer” aren’t uncommon. However, these Chuck Norris type claims are usually based on a single study involving cell lines propogated in test tubes and then subjected to various olive oil components of unknown bioavailabity at hundreds or thousands of times the concentrations naturally found in EVOO. Clearly, while these in vitro studies provide a good starting point for further research ‘in the field’, they, by themselves are too far removed from reality to justify the definitive claims that often follow their publication.

I was recently asked to review the myriad of health literature on extra virgin olive oil and put my naturally scientifically trained conservative part of my brain to derive a reasoned health statement regarding the benefits of extra virgin olive oil. Here’ what I came up with:

Extra Virgin olive oil is distinguished from all other oils in that it is richly endowed with a unique combination of monounsaturated fats, polyphenols and phytosterols.

A consistent body of scientific evidence exists that diets rich in these three natural components are associated with:

–  lower levels of “bad cholesterol” (LDL) and higher levels of “good cholesterol” (HDL).

–  lower levels of heart-unfriendly oxidised LDL’s.

–  reduced DNA oxidative damage which in turn is related to a reduced risk of some cancers.

–  reduced incidence of hypertension.

–  improved glycemic control, which is particularly advantageous to diabetic patients.

Agreed, the wording is measured, which may not suit everyones marketing style when it comes to explaining the health benefits of their EVOO. But hopefully this may give some direction on how to reasonably spruik the benefits of eating extra virgin olive oil.

Richard G.

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Around 7 years ago I was reacquainted with a small olive oil producer from Western Australia. It was a chance meeting – I was staying at a hotel attending a wine conference and he was on holidays with his family. After some chat, Colin went down to his car and generously gifted me a bottle of his new season olive oil.

I forensically began to scan the labels for the nitty gritties (as I do!). Variety Pendolino – check, oleic acid level in the high 70’s-good, nope, no free fatty acid level (why tfn I thought?). But much to my surprise, hand written on the back label was the amount of polyphenols the oil – around 550 mg per kilogram if I recall correctly. Now that’s a fair slab of polyphenols which was no doubt why he put it on the label.

Polyphenols are naturally occurring antioxidants. They are found in extra virgin olive oil in the range of about 100 to 1000 mg/kg (0.1 to 1 gram per litre) with an average of around 250-300 mg/kg (when measured in caffeic acid equivalents – more on this later). No other edible fat contains significant levels of polyphenols (virgin coconut oil is the closest at a paltry 50 mg/kg or less). While as a group they are widely believed to confer health benefits, they are also solely responsible for the bitterness and pepperyness of extra virgin olive oil. At over half a gram per litre, Colin’s oil did in fact prove to be a robust extra virgin olive oil. On top of this, polyphenols are one of the things that positively contribute to the shelf life of the oil.

So if they are important to healthfulness and oil stability why don’t more EVOO labels contain this information? Well one can only speculate, but it possibly due to a few reasons The first is the most likely – I’d guess that some producers don’t know of their existence and/or importance to healthfulness. Secondly, the official polyphenol assay is rather expensive as it is labour intensive and uses expensive reagents. Unlike many of the other basic oil chemistry that doesn’t change much if the olives are grown in the same place and the oil made in the same way, the polyphenol level can vary substantially depending on growing season, crop load and particularly on fruit ripeness at harvest. Therefore polyphenol levels need to be measured each year. A one size fits all approach doesn’t work for polyphenols.

When Colin gave me a bottle of his oil I can only say one thing with certainty – it didn’t contain the full quota of 550mg/kg of polyphenols as stated on the label. Not that he was cheating. Polyphenols decline from the moment the oil is extracted from the olive. Many are powerful antioxidants, so by definition they sacrifice themselves in the process of mopping up the rancidity causing free radicals generated from oxygen. But how quickly can polyphenols be chewed up in their protective role? The extent of the decrease depends on a lot of factors including the initial oxidative state of the oil, dissolved oxygen at bottling, pack size and type, type of stopper and storage conditions. A few scientific studies have looked at this. Del Caro et al. (2006) observed a 1/3^rd of the polyphenols drop away in the first 12 months after being stored in small bottles. Others have seen losses of up to 75% over 21 months (Gomez-Alonso et al 2005), and even when stored in tins under inert gas blanket, polyphenols fell by 30% over 15 months (Stefanoudaki et al. 2010). It’s is also worth noting that the biggest losses in polyphenols occurs during the early stages in the oils life, with a slow plateauing after the initial few months. From the data of Del Caro et al (2006).

Given the inevitable decline in polyphenols over its shelf life, then it would seem reasonable that producers who wish to give polyphenols levels should measure them at bottling and state that the given value is necessarily a maximum value. Consumers could then assess the style of oil and decide whether that oil was appropriate for the culinary use they had in mind.

To further complicate things, there are no internationally recognised methods for measuring total polyphenols, nor agreed units of measurements. As all the analysis that I’ve seen used are variants of two different method types, they probably get to the same point albeit in slightly different ways. However, the lack of an agreed unit of measurement is a real problem. The lack of an agreed unit of measurement is analogous to one person measuring something in inches and another in centimetres. Same length different values. For  polyphenols, “tyrosol equivalents” seem to be used extensively in some parts of the EU, while caffeic acid equivalents are commonly used by commercial laboratories, and gallic acid equivalents by research laboratories.

While polyphenols values are sometimes given on labels, the unit of measure is rarely so. I asked Colin what was the unit for his measure of 550 mg/kg. He didn’t know. “Just sent it to the lab and this is the number that came back” I asked which lab he used, and from this I inferred that the measure was in ‘caffeic acid equivalents’. From experience I knew that this put the oil well above average, and in the higher end in the general scheme of things. But how would the average consumer know whether 550 was high or low particularly when measured in one unit or another? Most still think that EVOO has to be extracted using a press and that EVOO smokes if you leave it on a kitchen bench in front of a sunny window!

Whatever the polyphenols value on the label it will decrease with time, so use up that EVOO and stock up with the new season stuff.

UPDATE 2013

The International Olive Council finally approved a method for measuring total polyphenols BUT as the method does not state the units of measurement, any polyphenol numbers you see quoted mean little. Arhhhh.

References

Del Caro, A. et al. (2006) Influence of technology, storage and exposure on components of extra virgin olive oil (Bosana cv) from whole and de-stoned fruits. Food Chem., 98, 311–316.

Gomez-Alonso et al. (2005) Evolution of major and minor components and oxidation indices or virgin olive oil during 21 months storage at room temperature. Food Chem., 100, 36-42.

Stefanoudaki et al. (2010) Changes in virgin olive oil characteristics during different storage conditions. Eur. J. Lipid Sc. Technol., 112, 906-914.

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I was recently asked to speak at the Australian Olive Association National Conference on what makes good show oils ‘tick’. The Australian EVOO show system is unique in that most shows ‘measure’ all of the exhibited oils in some way to either ensure eligibility or to allow the oils to be objectively allocated to classes based on their style. As a result of this, a significant body of data on the chemistry of Australian olive oils has been collected. Specifically the free fatty acidity (which is an indicator of the quality of the olives and how quickly and carefully the olives were turned into oil), and polyphenol level (which is a good indicator of how bitter and peppery the oil is –aka  style) have been collected by a number of shows over 5 or more years. As Chairman of these shows I get sent much of these data by the organisers at the conclusion of the show in a format that allowed me to get them together fairly easily. So while puting the seminar data together, along the way I collated data of the polyphenol levels of varietal oils. 2348 of them!

I selected 3 long running EVOO shows in Australia. These were 1) Royal Perth – a show that whilst being dominated by exhibits from Western Australia is well supported by boutique producers and has a wide variety of cultivars represented (typically 150+ entries).  2) Royal Canberra – much smaller, but is almost exclusively supported by small growers from cooler regions (80 odd entries) and 3) The Australian National – the biggest show with the most diverse range of exhibitors – micro volume through to millions of litres, but most importantly the oils exhibited here are from all states of Australia and therefore represent all climates – from cold to hot and even sub-tropical! (more than 200 entries per year).

I collated the data from the 2005-2010 Royal Perth and Australian National, and from the 2006-2010 Royal Canberra EVOO shows. These represent over 2,300 EVOO’s (ok – a few were surely exhibited in more than one of these shows, but it doesn’t happen that often – my guess is that <5% would fall into this category). So it’s a pretty good representation of what is/was being made.

Based on the information given by the exhibitor regarding whether the oil was varietal or a blend, I calculated the median polyphenol level by variety. To be included in the list, the oil must have been 100% from of a single variety and that variety must have appeared more than 30 times in these shows. Under this criterion Coratina just snuck in, as did Arbequina, but all of the others were very well represented – being major varieties in Australia (or in the case of WA Mission, Western Australia).

Here are the median (middle value) of polyphenols by variety. Note that in Australia (following the lead from the scientific community involved in measuring polyphenols), the results are given in “caffeic acid equivalents”. I won’t go into what that means specifically, but think of it as a unit of measure like a centimeter. If you see someone else quote a polyphenol in gallic acid equivalents or tyrosol equivalents then its like the same thing being measured in inches or pre-roman Calligulas or something. In short, oils measured in the same units can be compared, but you can’t compare an oil measured in tyrosol equivalents (which seems common in Italy), with another compared in gallic acid or caffeic acid equivalents.

Anyway – here are the results……

A few surprises. Manzanillo – wow. Considered as a table olive it does make oils that pack a punch. The much maligned Barnea – pretty well only grown in Australia and Israel showed that it isn’t meek and mild (not that it is a surprise to those who grow it, but perhaps to those who know nothing about it). Picual – I would have thought that it would be higher than low to mid range. Having said that, it is typically grown in Australia in warm to hot climates where it is irrigated – Conditions not conducive to high polyphenol production. The Italian mob – Corregiolla, Frantoio and WA Mission are closely grouped.

Coratina is lower than expected but it is a relatively new variety and as such is not strongly represented sample wise amongst the other varieties. If I were to repeat this in 5 years, I’d be surprised if Coratina didn’t move amongst the top 2 varieties in polyphenols.

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A set of proposed standards for olive oils sold in Australia and New Zealand were released late in December 2010 and are open for comment until the 25th of February 2011. They are available on the Standards Australia website.

After a bit of a read through, here are the things that caught my eye. I’ve categorised some as “big ticket items” – those that if accepted will significantlly change how Extra virgin and other olive oils are labelled and marketed in Australia and New Zealand, and “smaller ticket items” – those that are important but will have less impact. I’ve made some brief comments on each of the items at the bottom of the blog.

The Big Ticket Items

1.  The use of the term ‘cold pressed’, ‘pressing’ or ‘pressed’ on a label will be prohibited unless of course a producer actually uses a hydraulic press to extract the oil.

2.  The terms ‘pure olive oil’, ‘light or lite olive oil’and even ‘olive oil’ will be forbidden.  These oils will have to be labeled ‘refined olive oil’ or ‘refined  olive oil blend’.

3.  Best before dates will need to be supported by technical evidence, but cannot be more than 2 years after the oil was packed.

4.  Most of the chemical standards reflect those of the International Olive Council.

5.  The standard also broadly defines what type of containers should be used for the storage of olive oils. They must be appropriate for the stated shelf life, and must not affect the chemistry or quality of the olive oil contained within them.

Smaller Ticket Items

6.  The standards recognise the use of processing aids in the production of EVOO.

7.  Storage instructions that are necessary to achieve the stated best by date are required to be written on the label.

8.  Two new tests not recognised by the IOC are included in the new standard. These are measurement of 1) pyropheophytin A and  2) % of 1,2 diacylglycerides.

9.  The campesterol limit is higher than that of the IOC.

10.  The level of linolenic acid is higher than limits elsewhere.

11. A lower limit for polyphenols are absent.

12. If a food contains “olive oil” as an ingredient then it must necessarily state what grade of oil was used (EVOO, Virgin, Refined olive oil etc).

Notes on the big ticket items

1.  Terms as “cold extracted” will probably become the industry standard for EVOO’s

2.  All of these are simply different incarnations of refined olive oil that has had a miniscule amount of virgin olive oil added to them Under the proposed standards they will have to be labelled to reflect exactly what they are – refined!

3.  How best by dates can be objectively determined even given a raft of analytical parameters such as fatty acid profile and antioxidant level is unclear.

4.  The high FFA and peroxide limits set by the IOC and reflected in these proposed standards are in my opinion a slap in the face to EVOO consumers everywhere. Reducing these slightly would force large producers to work harder at putting good quality EVOO on supermarket shelves – and the overall standard would quickly improve.

5. This is a major shift in philosophy compared with standards elsewhere as it goes beyond the olive oil itself and recognises that the qualtiy of the oil is only as good as the container that holds it. This has the potential to significantly affect the types of packaging used. Clear glass, spray cans whereby the propellant may taint the oil, and possibly plastic packaging could fall outside the standard. I wonder who will decide whether they do or not, particularly given the constant advances in packaging technology?

Notes on the smaller ticket items

6.  These presumably include talc and enzymes. Both of these are widely used throughout the world, but to my knowledge no other standards acknowledge this reality.

7.  Consumer education by legislation?

8.  Pyropheophytin A is a compound formed when the green coloured chlorophyll degrades under heat. It is an indicator of the use of old oil in blends (a very common practice) and/or when an oil has been heated at any point during its manufacture or storage. These situations could include hot storage conditions or transport, or (the difficult to detect and illegal) practice of soft column deodorization.

1,2 DAG as a % of other DAG’s is an indicator of the general quality of the olives and their processing. Generally ‘suspect’ quality supermarket oils have low 1,2 DAG values around 30%.

9.  Campesterol is a natural plant sterol found in EVOO and other seed oils, notably sunflower. It is actually good for your health and does not detract from the oils shelf life. However the occurrence of elevated levels in EVOO has been used as an indicator of adulteration with sunflower oil. However, like all limits, they are necessarily arbitrary. The higher proposed limit in the new standard presumably is in recognition of a substantial body of recent research showing  that many olive varieties produce oils that naturally contain high levels of campesterol – often over the IOC limit. These include Koroneiki, Hojiblanca and (notably for the Australian industry) Barnea.

10.  Linolenic acid is a naturally occurring fatty acid in olive oil. It is easily oxidised and therefore high levels are detrimental to the shelf life of EVOO. However other factors such as polyphenol levels, bottling conditions and packaging are also important determinants of shelf life.

11.  There is an argument for a minimum level of polyphenols in an EVOO based on the fact that polyphenols contribute to the healthiness of EVOO and also to its shelf life. As someone who has done a few polyphenols measures myself it is worth noting that the accepted method of measuring polyphenols is somewhat unreliable due to the fact that it is impossible to extract all the polyphenols from the oil prior to analysis (most feel that +/- 10% error is about as good as it gets). This lack of reproducibility is particularly important when measuring polyphenols at the lower end of the spectrum which is where any limit for EVOO would be set.

So how will these proposed standards change after the review process? I guess only time will tell, but I bet there will be some pretty big interests who will furiously lobby in an attempt to have some of the big ticket items, and some of the new analysis removed from the standard. For the sake of Australian and New Zealand olive oil consumers I hope that the major thrusts of the new standards remain intact. They certainly are a big step in the right direction. But if you disagree, you can have your say until the 25th of February. I know I will.

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*****The last of these for a little while. Hopefully they’ve been of interest*****

Adding the preservatives butlyated hydroxytoluene (BHT), butylated hydroxyanisole (BHA) and tert-butylhydroquinone (TBHQ) to peanut oil increased its smoke point by 8-22C.

Wu and Yen (2004) Preventive effect of adding antioxidants on mutagenic compound formation in fumes of cooking oil. J. Sci. Food Agric. 84, 459–464.

Adding artificial preservatives BHT, BHA, TBHQ to vegetable oil increased its smoke point by around 10C.

Yen et al. (1997) Effects of Antioxidant and Cholesterol on Smoke Point of Oils. Lebensm.-Wiss. u.-Technol., 30, 648–652.

Comment: These fat soluble preservatives have to be added to all refined oils (canola, vegetable, grapeseed, flaxseed, ricebran etc etc) to give them a commercially acceptable shelf life. But it also improves the smoke point of the oil. So next time someone says – hey, I know that this refined oil has a higher smoke point than EVOO you might want to point out where some of that improvement came from! (and that the difference in smoke point between these oils and good EVOO i.e. with a low acidity, isn’t that different.)

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Field grown olive trees watered with saline water produced smaller fruit and lower oil content than those irrigated with fresh water. Saline irrigation resulted in oils with 20% higher polyphenols and higher proportions of oleic and linoleic fatty acids.

Ahmed et al. (2009) Saline water irrigation effects on fruit development, quality, and phenolic composition of virgin olive oils, Cv. Chemlali. Journal of Agricultural and Food Chemistry 57, 2803-2811. Comment: An unreplicated study.

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Nitrogen overfertilisation of mature Picual trees over three seasons resulted in reduced polyphenols and consequent bitterness and oxidative stability of the oil. Tocopherol level increased with fertilisation while the green and yellow olive pigments and fatty acid profiles remained unchanged.

Fernandez-Escobar et al. (2006) Olive oil quality decreases with nitrogen over-fertilization. Hortscience, 41, 215-219.

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The availability of nitrogen (N), potassium (K) and phosphorus (P) positively influenced flowering intensity in potted Barnea while only N and P increased fruit set. Beyond a certain level, increases in N reduced fruit load.

Erel et al. (2009) Flowering and fruit set of olive trees in response to nitrogen, phosphorus and potassium. Journal of the American Society for Horticultural Science, 133, 639-647.

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De-stoning three Spanish varieties (Picual, Hojiblanca, Manzanillo) prior to oil extraction resulted in polyphenol increases of up to 25%. The size of the increase was variety dependent, and was attributed to lower oxidation of polyphenols by the stone based peroxidase enzyme following its removal by de-stoning.

Luaces et al. (2007) Journal of the Science of Food and Agriculture, 87: 2721-2727.

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Moderate or intensive use of olive oil by 6,947 people aged 65+ was associated with slower age related declines in visual memory.

Berr et al. (2009) Olive oil and cognition: Results from the 3-city study. Dementia and Geriatric Cognitive Disorders, 28, 357-364.

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Extensive review of adherence to the Mediterranean diet on hypertension, cardiovascular risk, body-weight, cancer risk and rheumatoid arthritis.

Perez-Lopez et al. (2009) Effects of the Mediterranean diet on longevity and age-related morbid conditions. Maturitas, 64, 67-79.

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The incidence of obesity in 613 Spaniards was lower if they consumed olive oil or mixtures of olive and sunflower oil compared with when only sunflower oil was consumed.

Soriguer et al. (2009) Incidence of obesity is lower in persons who consume olive oil. European Journal of Clinical Nutrition, 63, 1371-1374.

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The solid fraction that develops in olive oil when chilled to refrigerator temperature contains a higher proportion of saturated fats and lower levels of polyphenols and tocopherol than the fraction that remains liquid. The liquid fraction contains more mono and polyunsaturated fats than the original oil. Both liquid and solid fractions had similar oxidative stabilities.

Jansen and Birch (2009) Composition and stability of olive oil following partial crystallization. Food Research International 42, 826-831.

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Destoning fruit prior to malaxation resulted in oils with higher polyphenols and C6 aldehydes (grassy flavoured compounds). This is because the pulp contains most of the polyphenols and flavour, and the stone contains most of the enzymes which degrade these during malaxation.

Servili et al. (2007) Effect of olive stoning on the volatile and phenolic composition of virgin olive oil. Journal of Agricultural and Food Chemistry, 55, 7028–7035

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The performance of 15 proposed crosses between Arbequina, Picual and Frantoio clones grown in Cordoba, Spain were presented. Most crosses had higher oil content (up to 6%) than their parents. However, despite being ‘mid field’ in terms of oil content, uncrossed Arbequina showed the desirable characteristics of very low fruit removal force and a lengthy ripening period.

De la Rosa et al. (2008) Australian Journal of Agricultural Research, 59: 46-51.

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Saline irrigation applied to mature Picual trees over an 8 year period did not effect shoot growth, fruit size or accumulated oil yield. The authors stessed the role of leeching of salts from the rootzone by natural rainfall on their results.

Melgar et al. (2009) Long term responses of olive trees to salinity. Agricultural Water Management 96, 1105-1113.

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