Slick Extra Virgin

This is the 3rd 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. This time, I present what I think is a reliable indicator of olive oil oxidation – K232.

FACT FILE

Name: K232 (short for absorbance at 232 nanometers).

What does it measure?: Level of oxidation.

How does it work? All olive oils contain some polyunsaturated fatty acids. These have a basic chemical structure that has two chemical double bonds amongst a long line of single chemical bonds. In an unoxidised state, the pattern of bonding is (Double-Single-Single-Double). But during oxidation of the fatty acid, the conga line of bonds changes to (Double-Single-Double Single).

Whilst this change in order might seem inconsequential, the oxidized rearrangement (D-S-D-S known as a ‘conjugated diene’) has a particular property in that (unlike its unoxidised D-S-S-D cousin), it strongly absorbs ultraviolet light at a specific wavelength of 232 nanometers.

So shining a beam of UV light at 232nm at an oil and measuring how much of it is absorbed can be used as a measure of the oils oxidation status. This is done using a peice of scientific equipment called a spectrophotometer. A schematic as to how the analysis works is shown in Figure 1.

Figure 1: A schematic showing the basic principle behind the K232 analysis for oxidation.

Unit of Measurement: absorbance units(au).

Does it affect extra virgin olive oil status?: Yes. To be extra virgin, the oil must absorb at less than 2.55 absorbance units at 232nm. In my opinion 2.55 is (like most of the IOC limits), way too lax. Most 2 year old oils can make the grade pretty comfortably. But if that is what they want……

Is it a measure of quality?: Yes. K232 has been shown to be a good predictors of the freshness of extra virgin olive oil in Australian competitions (Australia is the only country that routinely measures the chemistry of competition entries).

Official method degree of difficulty: Easy, but for accuracy, the oil sample needs to be accurately diluted by a technician with a relatively expensive solvent so the cost is moderate. It can be measured using cheaper NIR (Near Infrared Spectroscopy) method. However, like all NIR analysis, the validity of the accuracy depends squarely on the quality of the calibration available to the laboratory.

Typical effects of high readings of UV 232

– The oil displays tiredness and in some cases rancidity.

– Shorter shelf life.

K232 level in extra virgin olive oil is increased by:

– Delays between harvest and processing, incidence of fungal disease, olive fly attack and frost damage increase K232.

– Age.

– Oxidative bottling practices.

– Poor storage conditions.

Tweet This Post Facebook

This is the first of a short series explaining the common chemical analyses applied to extra virgin olive oil. I’ll start off with the most universal analysis of them all – “Free fatty Acidity” – or known to most of us as ‘Acidity’.

Name: Free Fatty Acidity or FFA

Better known as: ‘Free Acidity’ or simply ‘Acidity’

What does it measure?: The level of breakdown of the fats in extra virgin olive oil.

Analysis debuted: Circa 1890

Use by olive oil producers: Universal

Degree of difficulty: Easy. Can be done using basic lab equipment and little technical expertise. You can see me conducting an FFA analysis here

Official Iimit for extra virgin status: < 0.8%

Unofficial limit strived for by good EVOO producers: <0.2%

Direct effects of high readings of FFA:

• Lower smoke point (the temperature at which the oil starts to smoke when heated)
• Greasy mouth-feel/aftertaste
• Shorter shelf life

Typical indirect effects of high FFA:

• Reduced positive flavours and/or greater defective fermented like flavours.

Common causes of high FFA:

• Delays between harvesting and processing.
• Diseased/damaged olives particularly due to olive fly infestation and anthracnose (fungus).
• Bruising of olives during harvesting followed by processing delays.
• Olives harvested from the ground.
• Frozen/frosted olives.

What is Free Fatty Acidity?

Every fat molecules including that in olive oil is comprises 3 smaller parts called fatty acids that are connected together. Figure 1 is the typical fat molecule found in olive oil – three monounsaturated fatty acids called oleic acid linked together.

Figure 1: Extra Virgin Olive Oil Nirvana. A perfectly formed and intact fat typical of olive oil.

However, having 100% perfectly intact fats like those shown in Figure 1 molecules is “fat Nirvana”. Sort of like that place that the “Watchtower” magazines portray – where humans live in perfect harmony with dopey lions and really small monkeys (both of which are likely to kill you at any given moment, but somehow reassuringly, for different reasons). But, getting back to the point, extra virgin olive oil is a natural product, and therefore is less than perfect. Individual fatty acids can be chopped off the fat molecule if the olives are riddled with fungussy olive pestilence, are being gouged upon by olive fly maggots, bruised and battered during harvesting, or (more typically, and less dramatically) if the olives are left to even slightly decay in the interim between olive harvest and processing.

Figure 2: Formation of free fatty acids. The Pacman represents a lipase enzyme, but if you like, you can think of it as a Pacman.

Nature has devised a few ways of busting up intact fat molecules to form free (aka single) fatty acids. Her chopping utensil of choice are enzymes called lipases. They are found in the olive fruit, but in good fresh undamaged olives the lipases are harmlessly locked up in the olive cell away from the fat molecules that they desperately want to destroy. But when the olive cells are damaged in any way, the enzymes are able to escape from their compartments, and in frenzied attacks dismember the intact fat molecules freeing up fatty acid molecules (Figure 2). The more diseased the olive, or the longer the time gap between olive harvesting and processing, the more enzymatic activity and the higher the free fatty acidity.

Common misinterpretations/misrepresentations of FFA in olive oils.

“FFA is a good indicator of olive oil quality” –  Sort of right.

Free fatty acidity is widely acknowledged as a good index of general olive oil quality. While this is generally true, I have tasted many examples of higher FFA extra virgin olive oils that taste just fine, and conversely I have tasted many low FFA oils that are woefully defective. Take for example what is possibly the worst tasting defect in olive oil called muddy sediment. It has a foul (for olive oil) taste of parmesan cheese, baby vomit, salami, band-aids, horse stable and fetid milk (and combinations of these). An olive oil can pick up these characters from short term exposure to the particulate olive sediment that remains after oil extraction and which later falls to the bottom of a tank. The aroma compounds that contribute to this defect are very potent. Therefore whilst leaving the oil on the sediment may result in only a small break down of the fat (resulting in a small increase in FFA), this small increase in FFA can be accompanied by a large reduction in flavour quality.

“Refined olive oils have high FFA” – Very wrong!

Paradoxically nothing is further from the truth. Refined olive oils (i.e.  those labelled as pure, light and ‘olive oil’ ) have essentially zero FFA. Yep, zero. The confusion probably arises from the fact that badly made olive oils, i.e. oils with very high FFA’s are those destined for refining in the first place. The major purpose of the refining process is to remove the free fatty acids. This is effectively acheived by adding caustic soda which converts the free fatty acids to soap which can then be physically removed from the oil.

“The FFA of an EVOO increases substantially during storage” – Wrong again.

The production of free fatty acids from intact fat molecules is process that mostly involves the action of enzymes found within the olive which act in the presence of water. Once an olive oil has been properly extracted from the olive and most of the water has been removed (<0.1% remaining), further degradation in bottle leading to higher FFA is very unlikely. Typically, a properly processed EVOO with a low FFA of 0.2% at the time of processing, may get up to between 0.22% and 0.25% after 12 months of storage.  Ok, that’s a 10-20% increase, but when you consider that your typical inexpensive supermarket purchased EVOO from the EU typically starts at 0.60-0.80% the 0.02-0.05 increase in FFA due to storage is inconsequential.

“You can’t taste acidity in olive oil” – Got that one right.

The free fatty acids are so weak that they don’t have the ability to bother our otherwise very busy acid taste receptors.

“If the FFA of an olive oil is X% measured as oleic acid , this mean that the olive oil contains X% oleic acid”. – NO it does not mean that.

The “measured as oleic acid” is simply a unit of measurement. For a few anally retentive lipid chemists, it may seem important, but in reality, whichever fatty acid equivalent (pick one, any one), it really has bugger all effect on the final result. So everyone can ignore the “measured as” bit without any loss of meaning. That’s of course unless you are an anally retentive lipid chemist. But to satisfy the inevitable “% bi (oleic acid) curious” readers, I might have a go at explaining it in a forthcoming post.

Tweet This Post Facebook

Some Background

All edible fats primarily comprise of fat molecules which in turn are made up of fatty acids. The fatty acids are made up of chains of carbon atoms that are held together mostly by single chemical bonds. But every now and then a double bond appears on the chain. The majority of the fatty acids in olive oil (typically 75%+) contain only one double bond, whilst the fatty acids that dominate most other edible oils contain a higher number of double bonds.

The double bonds in fatty acids allow them to be ‘kinked’. Normally they kink in one particular direction (known as the cis form). Upon heating however, a small proportion of these fatty acids kink in the opposite direction (known as the trans form) as the latter form is the most chemically stable. Our bodies have evolved to be able to use the cis type of fat for normal bodily functions, but not the trans type, the consequence being that consumption of the trans form results in cardiovascular disease.

What’s Been Done

A number of scientific studies have looked at the amount of trans fat formation in edible oils during heating. However, most used either temperatures way above those needed to fry, or the oil was heated for lengths of time that you would only use if you accidentally left oil on the stove before heading out for a vacation. These studies were conducted to replicate the type and length of heating used in commercial deep frying operations.

What’s Been Found

I have included all the studies where the temperature was kept to a recommended frying temperature 180-200C and where there was no possibility of the food that was being fried (if that was the case) contained trans fats themselves. Unfortunately, in all the studies excepting one, the length of time that the oil was heated for far exceeded a typical domestic frying time. However, the data they provided do allow estimates of how much trans fat is formed when cooking for shorter periods of time that are more typical of domestic frying.

Not many of these studies used EVOO as it is an oil that is rarely if ever used for continuous deep fat frying in a commercial environment (comparing how fats perform when heated for long periods of time as occurs in commercial fat frying operations is the purpose of most studies, as the results have big $ implications). However, the same basic chemistry of isomerisation apply to all oils, so I have also summarised the results from these.

Table 1: Trans fat formation in edible fats after heating

*Estimated by linear interpolation at t=20 min. ** 1mg = 1/1,000^th of a gram (which is about 1/50th the weight of a drop of water)

Results

The level of trans fats of most of the edible oils, including olive oil, did not increase by heating using typical temperatures needed for frying. In olive oil, the largest increase was 5 x 1,000^th of a gram per kilogram of oil, and in EVOO no increase was observed.

EVOO is theoretically more resistant to trans fat formation, as being mostly monounsaturated it contains fewer double bonds than that of polyunsaturated fats such as sunflower or vegetable (soybean) oil. Also studies including those presented here have shown that natural antioxidants such as tocopherol and polyphenols which are abundant in EVOO inhibit the fat transing to the dark side.

But for some perspective – The average amount of trans fats in a 170 gm serving of french fries made by two major fast food chains (sampled from 20 countries) was found to be 4 grams (Stender et al. 2006). While this high level may be the result of prolonged high temperature heating, it is far more likely due to the high trans fat content (up to 25%) of the partially hydrogenated oils (1) that are commonly used in the fast food industry.

Based on the worst case result shown in Table 1, i.e. a 5 mg/kg increase in trans fat after heating, you would have to eat 310 servings of olive oil cooked French fries (53 kg or 140lbs worth) to get the same trans fat fix as a single serving cooked in an average fast food establishment (2).

Stender and colleagues in the New England Journal of Medicine stated that….

“Owing to the very high content of industrially produced trans fatty acids in certain fast foods, in many countries it is possible to consume 10 to 25 g of these trans fatty acids in one day and for habitual consumers of large amounts of this food to have an average daily intake far above 5 g”

Based on the studies above, heating 1kg of olive oil yields between 0 and 5mg of trans fat.

5 grams = 1,000 x 5 mg !

References:

Albi, T., Lanzo, A., Guinda, M.C., Perez-Camino, C. and Leon, M. (1997) Microwave and conventional heating effects on some physical and chemical parameters of edible fats. J. Agric. Food Chem. 45, 3000-3003.

Caponio, F., Pasqualone, A. and Gomes, T. (2003) Changes in the fatty acid composition of vegetable oils in model doughs submitted to conventional or microwave heating Int. J. of Food Sci. Tech. 38, 481–486

Hrncirik, K. and Zeelenberg, M. (2014) Stability of essential fatty acids and formation of nutritionally undesirable compounds in baking and shallow frying. J Am. Oil Chem. Soc. 91, 591–598 DOI 10.1007/s11746-013-2401-2

Rani, A.K.S., Reddy, S.Y. and Chetana, R. (2010) Quality changes in trans and trans free fats/oils and products during frying. Eur Food Res Technol. 230, 803–811. DOI 10.1007/s00217-010-1225-7123

Stender, S., Dyerberg, J. and Astrup, A. (2006) High levels of industrially produced trans fat in popular fast foods. New Eng. J. Med. 354, 1650-1652.

Kala, A.L., Joshi, V. and Gurudutt, K.N. (2012) Effect of heating oils and fats in containers of different materials on their trans fatty acid content. J. Sci. Food Agric. 92, 2227-2233.

Tsuzuki. W. (2012) Study of the formation of trans fatty acids in model oils (triacylglycerols) and edible oils during the heating process. JARQ 46, 215-220.

Yang, M., Yang, Y., Nie, S. Xie, M. and Chen, F. (2012) Analysis and formation of trans fatty acids in corn oil during the heating process. J. Am. Oil Chem. Soc. 89, 859–867. DOI 10.1007/s11746-011-1974-x

Footnotes:

(1) Hydrogenation is an industrial process mostly applied to polyunsaturated oils to make them semi-solid, and to increase their resistance to oxidation/rancidity. A by-product of partial hydrogenation is trans-fat production.

(2) given the reasonable assumptions of 1) oil retention of 15%, and 2) EVOO that had been heated for 20 minutes at 180C

Disclaimer: The information provided above is intended as general, and is not meant to be viewed as specific health advice.

Tweet This Post Facebook

What is Extra Virgin Olive Oil?

The ‘oily’ olive fruit juice extracted from fresh olives using a mechanical process which does not involve the application of excessive heat, additives or solvents.

Should I only buy first cold pressed oil?

Most extra virgin olive oil is produced by spinning the lighter oil away from the other heavier components of the olive such as water and olive matter using a centrifuge. So the term ‘cold pressed’ is redundant.

What’s the difference between extra virgin olive oil and other types of olive oil?

Extra virgin olive oil is a whole, unprocessed food and therefore contains higher amounts of healthy antioxidants. Conversely, ‘light’, ‘pure’, ‘olive oil’ and pomace oils are highly processed products.

Is ‘Pure’ olive oil better than Extra Virgin Olive Oil?

No. The word ‘Pure’ (together with ‘Light’) are purely marketing terms applied to refined olive oil. Pure sounds better than refined.

Do ‘light’ olive oils contain fewer calories than Extra Virgin Olive Oil?

No. All olive oils (and indeed all edible oils) have the same energy values.

This oil is bitter and peppery. Is it ok?

The bitterness and pepperyness indicates that the oil contains healthful antioxidants.. These characters complement the taste of strongly flavoured foods.

Is eating Extra Virgin Olive Oil good for my health?

EVOO’s contain significantly higher levels of monounsaturated fats and antioxidants than any other oil. These attributes are sought after by the health conscious.

Does the colour of olive oil indicate quality?

No. High quality extra virgin olive oils can appear emerald green through to golden yellow.

Where should I store Extra Virgin Olive Oil?

They should be stored in a cool dark place. For longer term storage where oils are used infrequently, refrigeration is a good option.

How long does Extra Virgin Olive Oil last?

They are best consumed young as fresh flavours and healthful polyphenols decline over time.  So when the new season oils are released, buy them.

I’ve heard that you can’t cook with Extra Virgin Olive Oil as its smoke point is too low. Is this true?

The temperature at which good quality (low acidity) extra virgin olive oil begins to smoke is significantly higher than what is needed to fry food (180C). So you can fry in EVOO.

Tweet This Post Facebook

Note: The copyright to this cartoon is solely held by the artist.

Tweet This Post Facebook

Tweet This Post Facebook

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.

Tweet This Post Facebook

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

Tweet This Post Facebook

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

Tweet This Post Facebook

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.

!

!

!

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.

Tweet This Post Facebook