When it comes to extra virgin olive oil, take an especially careful approach with respect to exposing it to excessive amounts of heat. All vegetable oils are susceptible to heat damage-much more so than the whole foods from which they were pressed or extracted. But in the case of extra virgin olive oil, the susceptibility is especially great. Here are some of the reasons that extra virgin olive oil requires special attention.
The effect of heat on its monounsaturated fats
All types of olive oil (including extra virgin) contain a large amount of monounsaturated fat. In fact, 70-80% of the total fat found in olive oil is monounsaturated. This monounsaturated fat comes from the monounsaturated fatty acid (MUFA) called oleic acid.
In comparison to all commonly used vegetable oils, olive oil is fairly unique in its high MUFA content. Canola oil comes close (60-70% MUFA), but many of the other commonly used vegetable oils, including sunflower, safflower, corn, and soybean oils naturally contain less than half as much MUFA as olive oil.
In general, monounsaturated fat increases the stability of a vegetable oil in comparison to polyunsaturated fat. This increased stability is related to the chemical structure of monounsaturated fat. MUFAs have fewer “reactive spots” than PUFAs (polyunsaturated fatty acids) and it is more difficult for oxygen radicals to interact with these kinds of fat. However, despite this lower reactivity, olive oil and other vegetable oils containing a high amount of MUFAs (like canola oil) still have relatively low smoke points and cannot withstand a large amount of heat. Unless these high-MUFA oils have been refined or conditioned in a way that increases their smoke point, they typically cannot withstand heats of much greater than 200-250˚F (93-121˚C) without incurring damage (the temperature of stove-top frying is 375-525˚F, or 191-274˚C). So even though the high-MUFA composition of extra virgin olive oil increases its chemical stability, it does not protect this wonderful oil from most stovetop or oven cooking temperatures.
It is worth noting in this discussion of MUFAs that the oleic acid found in olive oil has been the subject of expanding research interest when it comes to insulin resistance, cancer, and cardiovascular disease.
Recent studies have made it clear that oleic acid can directly alter the activity of certain cancer genes and appears to have anti-cancer effects that may be part of the Mediterranean diet’s health benefits. This primary MUFA in extra virgin olive oil may also help to lower a person’s risk of insulin resistance as well as favorably altering some of the blood fat patterns that can be associated with risk of cardiovascular disease.
Yet, to get these benefits it’s important to enjoy extra virgin olive oil when its MUFAs are best protected, which means at heats below 250˚F (121˚C).
Heat damages extra virgin olive oil
Research studies on the heat susceptibility of extra virgin olive oil tend to focus on higher heat ranges. Heats between 320-374˚F (160-190˚C) are most often used to determine the changes that occur in extra virgin olive oil due to heating. Studies on this subject repeatedly show that heats as low as 320˚F (160˚C) can substantially damage the phenols in olive oil. Although studies tend to expose extra virgin olive oil to heat for prolonged periods of time involving 1-3 hours, some studies have looked at relatively short heat exposures-sometimes as brief as 10 minutes. In all studies, heat exposure destroys key phenol components of extra virgin olive oil. At temperatures close to 350˚F (177˚C), for example, about 60% of the dihydroxyphenols in extra virgin olive oil are lost after 10 minutes! Hydroxytyrosol is another extra virgin olive oil phenol that gets damaged very quickly by heat, including heat as low as 320˚F (160˚C) according to published research studies. Alongside of the phenol loss that occurs with heat exposure is also the loss of vitamin E.
While I have not seen research studies that explored damage to extra virgin olive oil’s rich phenol mixture at temperatures lower than 320˚F (160˚C) I do not believe the extra virgin olive oil’s phenols are safe at temperatures lower than this! In fact, it seems highly likely to us that research studies involving lower temperatures would confirm damage to hydroxytyrosol and dihydroxyphenol at these lower temperatures-just less damage than already demonstrated at 320˚F (160˚C).
Until I see studies indicating otherwise, I will choose to play it safe with regard to heating extra virgin olive oil. These extra virgin olive oil phenols are simply too important to risk potential damage through unnecessary heating. The 200-250˚F (93-121˚C) temperature range is the one I feel safest with when it comes to the heating of extra virgin olive oil and protection of its phenols. This temperature range will work well for making sauce or for the warming of a dish that has extra virgin olive oil added just before this warming stage (but not during the actual cooking or baking process).
There are, of course, many dishes that do not require heating that will allow you to enjoy extra virgin olive oil. Healthy sautéed vegetables can be drizzled with extra virgin olive oil before serving. Extra virgin olive oil can be blended together with garlic and beans in a food processor to make a delicious dip. Extra virgin olive oil can be used in place of butter. There are also, of course, delicious salad dressings containing extra virgin olive oil that do not call for any heating whatsoever. In all of these circumstances, you’ll get to enjoy the great flavor of extra virgin olive oil along with the full benefits of its amazing health-protective phenols.
Health-e-Solutions comment: We have been cooking with EVOO up to temperatures of 350 degrees F. However, this article gives us reason to rethink our current practice in favor of using other oils for cooking at temperatures above 250 F.
- Artajo LS, Romero MP, Morello JR, et al. Enrichment of refined olive oil with phenolic compounds: evaluation of their antioxidant activity and their effect on the bitter index. J Agric Food Chem 2006 Aug 9;54(16):6079-88.
- Bendini A, Cerretani L, Vecchi S, et al. Protective effects of extra virgin olive oil phenolics on oxidative stability in the presence or absence of copper ions. J Agric Food Chem 2006 Jun 28;54(13):4880-7.
- Binkoski AE, Kris-Etherton PM, Wilson TA, et al. Balance of unsaturated fatty acids is important to a cholesterol-lowering diet: comparison of mid-oleic sunflower oil and olive oil on cardiovascular disease risk factors. J Am Diet Assoc. 2005 Jul ;105(7):1080-6.
- Bogani P, Galli C, Villa M, et al. Postprandial anti-inflammatory and antioxidant effects of extra virgin olive oil. Atherosclerosis 2007 Jan;190(1):181-6.
- Børsheim E, Kien CL, Pearl WM. Differential effects of dietary intake of palmitic acid and oleic acid on oxygen consumption during and after exercise. Metabolism. 2006 Sep ;55(9):1215 – 21.
- Brenes M, Garcia A, Dobarganes MC, et al. Influence of thermal treatments simulating cooking processes on the polyphenol content in virgin olive oil. J Agric Food Chem 2002 Oct 9;50(21):5962-7.
- Carrasco-Pancorbo A, Cerretani L, Bendini A, et al. Evaluation of the antioxidant capacity of individual phenolic compounds in virgin olive oil. J Agric Food Chem 2005 Nov 16;53(23):8918-25.
- Carrero JJ, Fonollá J, Marti JL, et al. Intake of fish oil, oleic acid, folic acid, and vitamins B-6 and E for 1 year decreases plasma C-reactive protein and reduces coronary heart disease risk factors in male patients in a cardiac rehabilitation program. J Nutr. 2007 Feb ;137(2):384 – 90.
- Cheikhousman R, Zude M, Bouveresse DJ, et al. Fluorescence spectroscopy for monitoring deterioration of extra virgin olive oil during heating. Anal Bioanal Chem 2005 Jul;382(6):1438-43.
- D’Evoli L, Huikko L, Lampi AM, et al. Influence of rosemary (Rosmarinus officinalis, L.) on plant sterol oxidation in extra virgin olive oil. Mol Nutr Food Res 2006 Sep;50(9):818-23.
- Davis BM, McEwan MJ. Determination of olive oil oxidative status by selected ion flow tube mass spectrometry. J Agric Food Chem 2007 May 2;55(9):3334-8.
- Del Carlo M, Sacchetti G, Di Mattia C, et al. Contribution of the phenolic fraction to the antioxidant activity and oxidative stability of olive oil. J Agric Food Chem 2004 Jun 30;52(13):4072-9.
- Gomez-Alonso S, Fregapane G, Salvador MD, et al. Changes in phenolic composition and antioxidant activity of virgin olive oil during frying. J Agric Food Chem 2003 Jan 29;51(3):667-72.
- Faine LA, Rodrigues HG, Galhardi CM, et al. Effects of olive oil and its minor constituents on serum lipids, oxidative stress, and energy metabolism in cardiac muscle. Can J Physiol Pharmacol 2006 Feb;84(2):239-45.
- Galvano F, La Fauci L, Graziani G, et al. Phenolic compounds and antioxidant activity of italian extra virgin olive oil monti iblei. J Med Food 2007 Dec;10(4):650-6.
- Gomez-Rico A, Salvador MD, La Greca M, et al. Phenolic and volatile compounds of extra virgin olive oil (Olea europaea L. Cv. Cornicabra) with regard to fruit ripening and irrigation management. J Agric Food Chem 2006 Sep 20;54(19):7130-6.
- Hrncirik K, Fritsche S. Relation between the endogenous antioxidant system and the quality of extra virgin olive oil under accelerated storage conditions. J Agric Food Chem 2005 Mar 23;53(6):2103-10.
- López S, Bermúdez B, Pacheco YM, J, et al. Dietary oleic and palmitic acids modulate the ratio of triacylglycerols to cholesterol in postprandial triacylglycerol-rich lipoproteins in men and cell viability and cycling in human monocytes. J Nutr. 2007 Sep ;137(9):1999 – 2005.
- Luaces P, Sanz C, Perez AG. Thermal stability of lipoxygenase and hydroperoxide lyase from olive fruit and repercussion on olive oil aroma biosynthesis. J Agric Food Chem 2007 Jul 25;55(15):6309-13.
- Masella R, Vari R, D’Archivio M, et al. Extra virgin olive oil biophenols inhibit cell-mediated oxidation of LDL by increasing the mRNA transcription of glutathione-related enzymes. J Nutr 2004 Apr;134(4):785-91.
- Mataix J, Ochoa JJ, Quiles JL. Olive oil and mitochondrial oxidative stress. Int J Vitam Nutr Res 2006 Jul;76(4):178-83.
- Menendez JA, Lupu R. Mediterranean dietary traditions for the molecular treatment of human cancer: anti-oncogenic actions of the main olive oil’s monounsaturated fatty acid oleic acid (18:1n-9). Curr Pharm Biotechnol. 2006 Dec ;7(6):495-502.
- Miles EA, Zoubouli P, Calder PC. Differential anti-inflammatory effects of phenolic compounds from extra virgin olive oil identified in human whole blood cultures. Nutrition 2005 Mar;21(3):389-94.
- Morello JR, Vuorela S, Romero MP, et al. Antioxidant activity of olive pulp and olive oil phenolic compounds of the arbequina cultivar. J Agric Food Chem 2005 Mar 23;53(6):2002-8.
- Moschandreas J, Vissers MN, Wiseman S, et al. Extra virgin olive oil phenols and markers of oxidation in Greek smokers: a randomized cross-over study. Eur J Clin Nutr 2002 Oct;56(10):1024-9.
- Nelson R. Oleic acid suppresses overexpression of ERBB2 oncogene. Lancet Oncol. 2005 Feb ;6(2):69.
- Owen RW, Mier W, Giacosa A, et al. Identification of lignans as major components in the phenolic fraction of olive oil. Clin Chem 2000 Jul;46(7):976-88.
- Pacheco YM, Bermúdez B, López S, et al. Ratio of oleic to palmitic acid is a dietary determinant of thrombogenic and fibrinolytic factors during the postprandial state in men. Am J Clin Nutr. 2006 Aug ;84(2):342-9.
- Pellegrini N, Visioli F, Buratti S, et al. Direct analysis of total antioxidant activity of olive oil and studies on the influence of heating. J Agric Food Chem 2001 May;49(5):2532-8.
- Perez AG, Luaces P, Rios JJ, et al. Modification of volatile compound profile of virgin olive oil due to hot-water treatment of olive fruit. J Agric Food Chem 2003 Oct 22;51(22):6544-9.
- Rotondi A, Bendini A, Cerretani L, et al. Effect of olive ripening degree on the oxidative stability and organoleptic properties of cv. Nostrana di Brisighella extra virgin olive oil. J Agric Food Chem 2004 Jun 2;52(11):3649-54.
- Salvini S, Sera F, Caruso D, et al. Daily consumption of a high-phenol extra-virgin olive oil reduces oxidative DNA damage in postmenopausal women. Br J Nutr 2006 Apr;95(4):742-51.
- Samaniego Sanchez C, Troncoso Gonzalez AM, Garcia-Parrilla MC, et al. Different radical scavenging tests in virgin olive oil and their relation to the total phenol content. Anal Chim Acta 2007 Jun 12;593(1):103-7.
- Soriguer F, Morcillo S, Cardona F, et al. Pro12Ala polymorphism of the PPARG2 gene is associated with type 2 diabetes mellitus and peripheral insulin sensitivity in a population with a high intake of oleic acid. J Nutr. 2006 Sep;136(9):2325-30.
- Thijssen MA, Hornstra G, Mensink RP. Stearic, oleic, and linoleic acids have comparable effects on markers of thrombotic tendency in healthy human subjects. J Nutr. 2005 Dec ;135(12):2805-11.
- Valavanidis A, Nisiotou C, Papageorgiou Y, et al. Comparison of the radical scavenging potential of polar and lipidic fractions of olive oil and other vegetable oils under normal conditions and after thermal treatment. J Agric Food Chem 2004 Apr 21;52(8):2358-65.
- Vissers MN, Zock PL, Katan MB. Bioavailability and antioxidant effects of olive oil phenols in humans: a review. Eur J Clin Nutr 2004 Jun;58(6):955-65.
- Votruba SB, Atkinson RL, Schoeller DA. Sustained increase in dietary oleic acid oxidation following morning exercise. Int J Obes (Lond). 2005 Jan ;29(1):100 – 7.
- Williams MJ, Sutherland WH, McCormick MP, et al. Normal endothelial function after meals rich in olive or safflower oil previously used for deep frying. Nutr Metab Cardiovasc Dis 2001 Jun;11(3):147-52.
- Wiseman SA, Tijburg LB, van de Put FH. Olive oil phenolics protect LDL and spare vitamin E in the hamster. Lipids 2002 Nov;37(11):1053-7.