Polyphenol levels in EVOO: To Label or Not to Label
admin | May 29, 2011Around 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 1/3rd 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.