Slick Extra Virgin

About a year ago an American producer and friend of mine said that he had heard from someone who had attended a conference somewhere that yeasts can survive for a long time in bottled extra virgin olive oil and that their activity is detrimental to the oil quality.

I was sceptical. Once bottled, extra virgin olive oil it is thought to be one of the most microbiologically stable foods. I’m pretty sure that if you took your grandmothers olive oil out of her manky pharmaceutical studded cabinet, that was left to her by her grandmother, you could chug down the whole lot of it and not get sick. You may re-acquire a taste for fast food, but you’ll wake up the next day feeling ok.

So when I recently came across the journal article titled

Effects of some oil-born yeasts on the sensory characteristics of Italian virgin olive oil during its storage (Zullo et al. 2013) I thought, ah there is the likely source of my American mates ‘Chinese whisper’ information.

So do olive oil producers really have get yeast counts done on the bottled oil to ensure that their oil doesn’t degrade faster than usual? I have to say that have always treated research reporting potential ‘problems’ that no one has noticed before, even after making the stuff for a couple of thousand years. But with an open mind, I looked at the ins and outs of the very detailed paper closely.

The researchers swabbed some EVOO’s, and ‘plated up’ what they found into a warm lagoon of yeasty heaven which allowed them to grow up enough yeast cells to inoculate a perfectly good extra virgin olive oil to assess the effects of yeast on oil quality during 4 months of bottle storage.

But keep in mind that the number of yeasts found in olive oil is pretty low probably due to the fact that the relatively waterless environment of an olive oil isn’t their favourite hang-out. However, after culturing them up in the laboratory, they added them back at a rate of (wait for it), 25gms of yeast for every 100L of EVOO. That is about the same amount of yeast that winemakers used when they ferment grape juice into wine. In laymans terms ‘bucket loads’. To put the amount they used into an olive oil perspective, they estimated that they added around 100,000 yeast cells to every 1ml of oil. Compare that to the 1,000 odd yeast cells per ml that are naturally found in olive oil (based on a survey of 14 commercial olive oils from the Liguria and Central Italy, Zullo et al. 2010).

So what effect did adding 100x the typical number of yeast to an olive oil and leaving it for 4 months have?

Probably not surprisingly, the yeasts were shown by the researchers to produce all sorts of evocative (to a microbiologist anyway) enzymatic activity – Peroxidase, tyrosinase, phenoloxidase, and b-glucosidase, which could potentially degrade olive oil and affect its quality. But we all have ‘potential’ don’t we?

Here are the effects that matter. The effects on the chemistry and taste ….
Table 1: The effect* of inoculating with these large amounts of yeast and then storing the oil plus yeast for 4 months.

*The researchers looked at the effects of half a dozen yeast types. I averaged their effects and presented them with changes to the same oil that had not been yeast inoculated and stored for the same length of time.
^Approximate value as the raw data was read off a figure, but it gives you an idea.

They also found that yeast inoculation modified the profile of aroma compounds, with yeasty oils having lower amounts of the grassy tasting C6 compounds. Interestingly though, many other compounds that are normally associated with poor tasting olive oil (C7, C8 and C9’s) did not increase – indeed many of them decreased in the presence of yeast.

There are a few ways of looking at these results, including that you could add yeast to your olive oil to improve its oxidative stability! Lower peroxide values and lower secondary oxidation values are good things right? Well that is what the data suggests. Others would look at the results and emphasise that polyphenols were reduced by 10%, and the oil was less fruity and some yeast produced a faint muddy aroma. But, despite the fact that the researchers appeared to try to use experimental extremes to induce an effect by all manner of yeast types, they barely dented the quality of olive oil.

Where an extra virgin olive oil is bottled immediately after extraction, and is still ‘murky’, then maybe, just maybe these results may apply. However, oils of this type are meant to be consumed immediately as they have a high moisture content and contain relatively large amounts of vegetative solids. It is arguable that they would probably go muddy even without any yeasty action, as keeping vegetable solids in a highly anaerobic (airless) environment will most likely do that anyway.

So hopefully we won’t be seeing tests for yeast cell counts any time soon. We have enough tests already.

Zullo, B.A., Cioccia, G. and Ciafardini, G. (2013) Effects of some oil-born yeasts on the sensory characteristics of Italian virgin olive oil during its storage. Food Microbiology, 36, 70-78.

Zullo, B.A., Cioccia, G. and Ciafardini, G. (2010) Distribution of dimorphic yeast species in commercial extra virgin olive oil. Food Microbiology, 27, 1035-1042.

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To many people, the characteristic smell exuded by the linseed oil that their grandfather kept in his mancave for 35 years IS the aroma of olive oil. For them olive oil is supposed to smell like that, and it is exactly how they like it. I have always considered these people ‘misguided’. Surely, they must have learned to like rancidity. Perhaps a great-aunt from Omaha or Boise led them astray in their early childhood by force feeding them stuff out of the medicine cabinet. You know, the manky stuff with the yellowed label that needed carbon dating to validate the century in which it were made. But recent research using mice (Nankano et al. 2012) suggests that unsavory bullying from an uninformed, stodgey great-aunt might not be necessary to appreciate the delights of rancidity after all.

So here is how it went..

To provide a base-line, mice were presented with two bottles of the same non-oxidised olive oil in their feeding cage for three weeks. The amount consumed from each bottle was the same showing that the mice didn’t have a favourite restaurant strip.

But then one of the feeding bottles of fresh oil was replaced with another containing oxidised olive oil (left in a hot place in an open bottle for 3 weeks). The mice given the choice, consumed 10 times more of the oxidised oil than the fresh oil. The experiment was repeated using a heated refined olive oil. Same result – the mice chose to eat a lot more rancid oil than fresh oil.

Furthermore, the more the oil was oxidised (they made up blends of fresh and oxidised), the greater the preference for it. Mice that were anosmic (had no sense of smell) didn’t prefer one oil type over another suggesting that the aroma and flavour of the olive oil was the driving factor in preference.

Does this mean that rancid oil is the default for preference, and that appreciating fresh olive oil is a learned response? But leaving this important philosophical aside what I really want answered is – how the hell did the researchers identify anosmic mice (the ones without a sense of smell) from the non-anosmic mice? Did they put them under a bed doona and record which ones tried to escape?

Source: Nakano et al. (2012) Effects of aroma components from oxidised olive oil on preference. Bioscience, Biotechnology and Biochemistry. 77, 1166-1170.

You can read the article here: https://www.jstage.jst.go.jp/article/bbb/77/6/77_120861/_article

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a)      Mechanical processing includes methods that do not use solvents or excessive heat to extract the oil.  These methods include centrifugation and (now, rarely) pressing.

b)      Pomace is the mix of skins and crushed olive seeds left over after most of the olive oil and water have been mechanically extracted from the olive paste.

c)      Usually hexane is the solvent used.

d)     Refining involves a number of steps which involve the addition of strong acids and bases, and the application of processes such as chilling, washing, centrifugation, filtration and deodorisation.

e)      Pure olive oil is no ‘purer’ than any other olive oil. ‘Light’ olive oil does not have fewer calories than any other oil. The term ‘light’ refers to its lighter colour, aroma and flavour – a result of the oil having been refined.

More information on the difference between olive oil types can be found here

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One of the most enduring myths about extra virgin olive oil is that if you heat it then it will produce more free radicals (and is therefore be more ‘toxic’  – or more appropriately ‘detrimental to your long term health’) than other edible oils.

The belief in the binary model of ‘EVOO when heated is ‘toxic’, but every other fat when heated is not’ is plainly ludicrous. Why? Because the natural chemical composition of all edible fats including EVOO overlap, and in some cases significantly. For example while EVOO contains on average around 75% of the fatty acid oleic acid, canola oil averages around 60%,  and high oleic sunflower about the same or higher than EVOO. All oils contain sterols and tocopherols, and while EVOO has significantly more polyphenols than any widely used edible fat, polyphenols are more likely to inhibit the formation of free radicals Therefore unless the oil extracted from olives is somehow able to find a way to defy the basic laws of fat chemistry, then the idea that olive oil becomes more ‘toxic’ than other oils when heated can’t be justified.

Recently a paper was published in the peer reviewed journal Food Chemistry (Tomassetti et al. 2013) which goes a long way to debunk the myth.

What they did:

• A peanut oil and extra virgin olive oil that had been stripped of its polyphenols were heated to 180C and air was bubbled through them over a period of hours in an effort to mimic extreme heating conditions

Result:

• Heating peanut oil and EVOO (even without antioxidant polyphenols) resulted in the same degree of free radical formation. (Figure 1).
• The longer you heated these edible fats the more free radicals they formed – both of them!

Tomassetti et al. (2013) PO=peanut oil, EVOO=polyphenol stripped extra virgin olive oil. If the error bars shown at the top of the bars overlap then that means that there is insufficient evidence of a difference in free radical formation between the oil types upon heating.

What they did:

• A peanut oil and an EVOO (with its natural polyphenols) were heated and compared with respect to rancidification.

Result:

• More heat energy was needed to start the oxidation of fat molecules in EVOO than peanut oil which suggests that EVOO is more resistant to rancidification when heated. The authors attributed this to the polyphenols in the EVOO. “the higher thermal stability of triglycerides contained in the whole EVOO is probably due to the high concentration of polyphenols contained in it”

Other comments:

The researchers used an EVOO stripped of polyphenols as phenolic compounds interfered with the measurement of free radical production. Given that polyphenols mop up free radicals, I would predict that the net production of free radicals in heated phenolic rich EVOO would be significantly lower compared with refined edible fats that contain few if any phenolic compounds.

The oils were heated to a reasonable cooking temperature. They were not burnt! Once an oil burns a whole different bunch of chemical reactions come into play. So is burnt EVOO any more or less healthy for you than burnt edible oil X? Probably not, but who cares.Just don’t use burnt oil of any type. It isn’t good for you. That is what the knobs on the front of the stovetop are for.

Source:

Tomassetti et al. (2013) Biosensors for monitoring the isothermal breakdown kinetics of peanut oil heated at 180 C. Comparison with results obtained for extra virgin olive oil. Food Chemistry, 140, 700-710.

http://dx.doi.org/10.1016/j.foodchem.2012.10.131

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So what do all those chemical analyses found in lab reports mean?

There are dozens of them. Some have been accepted as indicators of quality, others suggest how long an extra virgin olive oil will survive on the shelf, while other analyses tell a story about the taste style of the oil (and therefore how it is best used in the kitchen). However, most have been developed in an effort to identify olive oils that have been adulterated with other oils. However, as these limits are necessarily arbitrary, they only suggest rather than prove adulteration.

I have provided some ranges and averages that typify good to excellent extra virgin olive oil in addition to the official limits which are often set to accommodate the constraints of the big EU packers to produce quality olive oil.

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Sources: All data with the exception of e- ‘fresh’ samples are from commercially produced extra virgin olive oils.

a-              2005-2010 Australian National, Royal Perth, Royal Canberra Extra Virgin Olive Oil Shows (n=2,356). Compiled by R. Gawel –unpublished.

b-             2005 data, New South Wales Department of Agriculture – unpublished (n>200).

c-             Australian Olive Oil Association National Olive Oil Survey – unpublished (n>200).

d-             Mailer (2007) (n=1800)

e-              Mailer and Ayrton (2008) (n=21 fresh, n=6 EU supermarket)

f-              Anon (2010) Oli Extravirgini di Oliva di Firenze Selezione 2010 (n=33)

g-              Gawel and Rogers (2008) (n=327)

#- Measured as caffeic acid equivalents

^- ‘unsaturated’ refers to fats that contain more than one double bond somewhere in their chemical structure. Monounsaturated fats have health benefits over saturated fats (ones with no double bonds).  However polyunsaturated fats (i.e. those with two or three double bonds) such as linoleic and linolenic acid are more prone to oxidation and therefore degrade (go rancid) more quickly.

^^ – b-sitosterol, d-5-avenasterol, d-5-23-stigmastadienol, Clerosterol, Sitostanol, d-5-24-   stigmastadienol

*- olive oil is a complex natural product. As such the amount of individual components in olive oil varies. As a result, unadulterated oils may be high in one or more components normally associated with adulteration practices. For example the varieties Barnea and Koroneiki often produce oils that contain naturally high levels of campesterol.

Disclaimer: This table should be used only as a guide. While every care was taken in the compilation of this table, the author takes no responsibility for any inaccuracies.

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“The upshot was restaurants would have to spend a small fortune buying in specially prepared bottles of tamper-proof olive oil to serve to customers, many of whom had never realised there was a problem in the first place”;The Daily Telegraph UK 26th May 2013

Recently the European Commission on Agriculture put forward plans to ban refillable containers containing olive oil on restaurant tables, insisting they be replaced with unopened labelled bottles with tamper proof seals. The ban was immediately rescinded after considerable consumer and media backlash particularly from the non olive producer nations. Presumably the ban was proposed to in an effort to eliminate the practice of restauranters diluting their extra virgin olive oil at the point of ‘sale’. I have italicised ‘sale’ because in most cases olive oil is given away by the restauranteur which is a point that the proponents of the ban seemed to have not adequately considered.

Before I begin, I declare that I am relaying some experiences from an Australian context. However, I cannot see why my arguments would not stand up in the context of European restaurants where the regulations were to apply.

I have two friends ‘M&M’ who co-own a busy café in Adelaide, Australia. When I say, busy I mean the bustling, noisy type with each table hosting 3 covers (different customers) a night. The café like many others like them, offers a diverse range of cuisines including Mediterranean and also offer complementary good genuine extra virgin olive oil for customers as an alternative to butter.

Like many local restaurateurs, they source their extra virgin olive oil from a local producer – from the McLaren Vale region, 30km from the city. They know the producer personally and have used his oils for some years. They trust him, and have no reason not to. I also know him and he is a fair bloke who is understandably proud of the EVOO’s that he produces. By selling in bulk he can profitably supply M&M with quantities of oil at good price.

I asked M the hypothetical question. “What if the Government insisted that you had to serve the extra virgin olive oil to tables in small unopened labelled bottles so that the customer could be certain that you weren’t ripping them off?”

She looked at me almost quizzically and calmly answered …. “I wouldn’t” (serve it at all)

(the rest I paraphrase, because I was just another customer and they were very busy)

R: Why wouldn’t you?

M: Hey, I give this stuff away for free. It costs me money. I don’t have to do it. I’m sure if I didn’t offer it, and put butter in its place, very few people if any would push my buttons over it.

R: But surely olive oil is an important ingredient and part of the overall culture of eating?

M: Both I and my chefs love extra virgin olive oil and the flavours that the oils brings, but the restaurant biz is difficult. Margins are tight. We look carefully at every menu item, and every input – costing it out carefully. Is it necessary? Are there less expensive alternatives? What impact does it have on the bottom line? Because ultimately, unless you can make a living out of the business you just shut your doors. And one thing for sure, I don’t owe olive oil producers or any other ingredient supplier a living.

Now I’m pretty sure that when the European Parliament who immediately asked the European Commission to go back to the drawing board and consult with consumer groups and restaurant owners, that the above conversation is the sort they had in mind.

So what effect would a policy of having to use labelled unopened bottles rather than dispensing oil into bowls or cruets?

For the small producer, selling in bulk is often the only way in which they can make a decent return. Having to bottle, tamper-proof seal and label adds a significant cost, and as every producer knows, the relative cost of package to its contents increases as the package volume decreases. These additional costs will eventually have to be passed onto the restaurant either in part or in full. Given that most restaurants do not charge for the olive oil they serve, clearly having to pay more would be rather unpalatable and could potentially lead to EVOO being replaced.

To M&M the idea of having small bottles around the café also makes no sense. There is the issue of storage and increased waste handling and costs associated with disposal. “We’ve got enough sh*t to get rid of each night, why would I want any more”.

So what about the argument that having a branded bottle in front of the restaurant customer will promote the producers brand and lead to additional sales. I think it would be naïve to think that many restaurant customers would care enough to take much notice. Furthermore, most small producers have limited or no retail outlets outside their farm gate or local market, so even if a restaurant customer cared to notice the brand of the oil, I would presume that the chances of them chasing down a bottle the day after is very unlikely. But yes, it is possible that it could lead to sales, but the costs of compliance would probably outweigh the small marketing advantages gained.

So why was the regulation proposed in the first place?

The official line is that it was introduced in an attempt to eliminate fraud in the restaurant trade.

However the measure does not address the biggest cause of fraud. That is the adulteration, or misrepresentation of the EVOO BEFORE it was packaged and supplied to the restaurant. While supporters of the proposed regulation will argue that having a bottle identified by a label will discourage this,  I would argue that such measures have not stopped adulteration or passing off poor quality oil at the supermarket retail level where similar labelling requirements exist. So why would the measure work at the restaurant level? Unless policing occurs via chemical testing then the problem will persist.

I would also argue that the regulation implies that the major cause of adulteration in the food services industry is the restaurateur. Such beliefs only serve to deflect scrutiny from up-stream sections of the distribution chain.

Also being somewhat of a cynic, I noted that things of this magnitude don’t happen in the olive world very often, and nothing happens on a broad institutional level unless the big olive oil marketing conglomerates support it.

Who would most likely profit from such a policy change? In short, packagers- and specifically those with the technical capability of bottling to the stringent specifications that were being called for. And who are the big packagers? Answer: The vertically integrated companies that buy oil in bulk before blending, bottling and marketing them under the well known supermarket brand names. I also wonder what share of the restaurant market they currently have? My guess is less than they would like.

And where would this stop? What about opened bottles of wine served by the glass? I’ve been to plenty of eating establishments where the wine tasted like it had been opened for a while. I’ve politely brought the issue to the attention of the server, and they have replaced the glass of wine with that from a freshly opened bottle. No problems. Will opened bottles of wine be banned next? Unlabelled pepper?

I’m all for cleaning up the EVOO industry of fraudulent practices, but realistically was this the right way of going about it? I think not. The idea reeked of an industry looking inwardly, rather than to the needs of its customers. It really was pretty dumb.

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Here is something a little different.

Do you think you know about olive oil and extra virgin olive oil?

Well this online cross word will test you.

It’s easy to use. Open the link and the crossword will appear. Click on an word box and the question will appear. Type in the answer. Move onto the next word until you finish. If you type in a word is too long or short it will tell you.

Click the solve box if you want to cheat. Hopefully even if you don’t get all the answers, you will learn something along the way.

Here’s what it looks like….
Click here to start

Good luck!

Incidentally, the software used to create this crossword is free, intuitive, easy to use, and works seamlessly. You can use it to create both online and paper based crosswords. The crossword contains a link to the creators.

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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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Olives did not make up a significant area of land in Southern Spain the 20^th century. In the mid 18^th century the land dedicated to olives was around 1/20^th of what it is today. Groves as we know them today were rare. Olive trees were scattered amongst other crops particularly cereals which made up over 50% of the arable area, and were managed more as a forestry enterprise with very few inputs and little management. Olive trees were grown as they provided a wide range of products – pomace and leaves for fuel and livestock feed, oil for lighting and for soap production. Olive wood was used for fuel at twice the rate as forest wood in 1750, and the percentage of olive wood to forestry wood used for fuel increased up until the early 1900’s. Clearly the diversity of outputs was well suited for small subsistence landholders.

However, in 1750 only 8% of the oil produced was eaten, the rest was used for lighting and animal production. 90% of fat intake in Baena (a major olive growing region in Southern Spain) was animal fat, with olive oil making up the remainder. It was only around 1900 when the consumption of olive oil first surpassed that of animal fats,

The final decades of the 20^th century saw olive growing increase significantly. Area to olives in Andalucia increased by 300,000 ha and oil production tripled to current levels. The authors attribute this to increased supply due to industrialisation of agriculture, modernisation of mills (both resulting in significantly higher oil yields per ha), and the introduction of EU subsidies. On the demand side, appreciation of the health benefits of olive oil has stimulated worldwide demand. Finally, olives were not seen as a single crop in the Andalucian landscape on any scale until well into the 20^th century.

InfanteAmate(2012)The Ecology and History of the Mediterranean Olive Grove: The Spanish Great Expansion, 1750 ­ 2000. Rural History. 23: 161­-184 doi:10.1017/S0956793312000052

Comment: Very interesting as this paper presents evidence that suggests that the use of olive oil as a major part of the Med diet may be a relatively recent phenomenon. No doubt the olive tree was an important crop as it provided a number of resources for small scale subsistence farmers. As one of my friends commented. Perhaps in 1750 when people died of TB, diptheria, plague or even minor infections, the concept of eating something healthy to prolong life may have been a bit weird.

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Normally I comment after presenting research results but this time I’ll comment first by saying that this was 20 minutes of my life that I will never get back. This paper compared 2 phase, 3 phase and a traditional press with respect to total polyphenol content and polyphenol type in the oil, waste-water and pomace. The researchers also measured antioxidant activity so they could comment on the healthfulness of the oils produced by the three systems. There was extensive analysis of the types of polyphenols using high performance liquid chromatography.

However when I later read the methods carefully, the researchers had used three different batches of olives, with each batch being a different variety grown in different places, with a different batch being processed using each of the different extraction methods. e.g. Variety X from place A was processed by press, Variety Y from place B was processed by 2 phase and Variety Z from place C was processed by 3 phase. How could they possibly think that they could compare systems when the effect of processing system is totally confounded with the effect of the olive source? I won’t even summarise with what they came up with (although the results seemed in line with expectations).

An example of the danger of just reading the abstract.

Klen and Vodopivec (2012) The fate of olive fruit phenols during commercial olive oil processing: Traditional press versus continuous two- and three-phase centrifuge. LWT – Food Science and Technology 49, 267-274  doi:10.1016/j.lwt.2012.03.029

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Enclosing the vertical centrifuge in a container filled with argon with an oxygen level of 3% reduced dissolved oxygen in the oil by 6.8 mg/L (71%), peroxide values by 3.8 (44%), and K232 by 0.46 (27%) compared with decantation under air. FFA and polyphenol level were unchanged.

Masella et al. (2012) DOI: 10.1002/ejlt. 201100400

Comment: Others have found that vertical decanting is the primary cause of dissolved oxygen in EVOO. The large effects reported here support this. However how this could be put into practice is unclear.

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Olives were stored in plastic bags under high CO2 modified atmosphere and at 5C for up to 21 days prior to being processed. The first sampling day was at day 7. Free fatty acidity increased as expected with storage time, but the increase was lower under the modified atmosphere and at 5C compared with when the olives were stored in a normal atmosphere at room temperature. Over the most realistic storage time used in this study (7 days), total polyphenols and radical scavenging activity fell except when the olives were stored in the modified atmosphere at the lower temperature. The bitterness index increased with storage time.

Ben Yahia et al. (2012) Quality, stability and radical scavenging activity of olive oils after Chétoui olives (Olea europaea L.) storage under modified atmospheres. Food Science and Technology International 18: 353-365. DOI: 10.1177/1082013211428102

Comment: Only a small amount of olives were stored (1.5kg). It would be interesting to see if the same results were observed in a more realistic situation of having bins of olives whereby heat builds up due to fermentation, and that the olives are generally starved of oxygen in these bins due to carbon dioxide production. The realistic storage time comment was in the context of, most producers try to keep the time between harvest and processing to a minimum. However, due to unusual circumstances (e.g. equipment breakdown), sometimes olives have to be stored for a short time. Ok, not 7 days, but this was the first time point of analysis in this study.

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A great deal of mysticism surrounds extra virgin olive oil – what it is, how it is made, and (in some cases) the miraculous things that it can do to your health. Leaving aside the alleged positive effects of consumption on erectile dysfunction (Esposito et al. 2006), acne (Skrosa et al. 2012) and just about every other ailment of man – a more recent trend is trying to validate whether you have purchased real extra virgin in the comfort of your own home using readily available household implements.

One of the myths that have been circulating for some time is that you can tell an extra virgin olive oil by whether or not it solidifies in the fridge. So armed with only a bottle of oil and a working fridge, you too can foil those sophisticated adulterers of extra virgin olive oil. Like a lot of enduring myths this one is based on a tiny bit of science, and a lot of misguided logic.

Recently the social media has been ablaze with a new DIY test for extra virgin olive oil – and all you need this time is a green laser pointer.

Here is how it supposed to work

Shine the green laser through a clear glass bottle containing the oil. If the laser light appears orange or red as it passes through the oil, then it is extra virgin olive oil. If the laser light remains green as it passes through the oil then it is a fake.

Here is an image showing how it works:

Source: Gordon (2012)

First a disclaimer (of sorts). I LOVE lasers!. When I studied physics at university in the late 70’s one of those (then big) things cost about 2 years of a scientists salary. Now you can pick one up from your local disposal store for about the price of packet of crisps. And you can shine them on things from really far away!

But back to the point (forgive the pun). The ‘green laser test’, like the fridge test has a modicum of science behind it, which of course makes it believable, but also dangerous in that it leads people to believe that detecting fraud in extra virgin olive oil is a simple task.

So here are the reasons why both green laser light goes red in extra virgin olive oil, and also why it isn’t a good test for authenticity of extra virgin olive oil.

All extra virgin olive oils naturally contain the green coloured plant pigment chlorophyll. Some oils contain a lot, others very little. But as EVOO is simply the mechanically extracted oily juice from crushed olives, if any of the olives were green (which some always are), or there were some leaves mixed in with the olives (ditto), then the resultant oil will contain chlorophyll. It’s not a matter of if, but only how much.

Laser light is different from ordinary light. Light is a mixture of various wavelengths while lasers emit light of a single wavelength (in the case of green, the wavelength is 532 nanometres). Here is the important bit. Light of a specific wavelength emits a specific amount of energy.

In the case of green laser light, this is EXACTLY the right amount of energy to excite chlorophyll molecules into a higher energy state (wait for it)…. But everything that is excited in nature, must return to a more relaxed state sooner or later.  When the green laser excited chlorophyll relaxes, it releases a little less energy than it took in, in the form of longer wavelength light at 620 nanometres – or to you and I – reddish-orange light. This phenomenon is called fluorescence, and the it has known to occur in chlorophyll since 1838!

But unlike humans who relax in lots of different ways, molecules like chlorophyll are restricted by the laws of nature to relax in this very specific way – Green in, Red-orange out. So that is why you see that distinctive reddish-orange fluorescence you see when you shine green laser light through an EVOO. It’s just chlorophyll.

For the skeptical. Figure 1 shows the fluorescent spectra of chlorophyll– I’ve added the colour bar so you can relate wavelength to colour. Figure 2 shows the actual fluorescence spectra for an extra virgin olive oil, and for two refined olive oils. You can see that the maximum of the spectra for chlorophyll and for EVOO correspond exactly.

Figure 1: Adapted from Krause and Weis (1984)

Figure 2: Source – Fawaz et al. (2009)

Here’s why fluorescence in extra virgin olive oil is not a particularly shining example of a valid EVOO adulteration detection methodology.

If I blended some legitimate extra virgin olive oil which will fluoresce, with a refined oil (olive or seed) that won’t fluoresce, the resultant (non-extra virgin) blend WILL fluoresce. Remember that not all EVOO’s contain a lot of chlorophyll. Some are green, but many are not, so different extra virgin olive oils will fluoresce to different extents. So if you add some refined oil to an EVOO rich in chlorophyll it will fluoresce exactly the same as a low chlorophyll extra virgin olive oil. The former is not legit – the latter is. But it’s orange time for them both.

Lastly, it would be pretty easy to make a refined olive oil fluoresce even without adding any EVOO at all. Add a few olive leaves, or industrially available natural chlorophyll, or (possibly*) synthetic chlorophyll (E411) and your refined olive oil will fluoresce brighter than a Christmas tree in the eyes of a 4 year old. Adding chlorophyll or its synthetic analogues to refined olive oil has been one of the tools of the trade of adulteraters for years. Want to make a refined olive oil look Tuscan and increase its value 10 fold? Add chlorophyll. The green laser will swear that it’s a legitimate extra virgin.

And that is how myths are born.

References:

Esposito et al. (2006) doi:10.1038/sj.ijir.3901447

Gore (2012) Phys Teach. 50: 377-378.

Krause and Weis (1984) Photosynthesis Research, 5: 139-157.

Skrosa et al. (2012) doi: 10.1177/1403494812454235

Fawaz et al. (2009) doi: 10.1063/1.3250101

* synthetic chlorophyll is a compound with a copper core, rather than a magnesium core like real chlorophyll, something that would most likely would affect fluorescence.

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