What is the difference between extra virgin olive oil and the other vegetable oils?

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A wide range of vegetable oils obtained from fruits or seeds are commercially available. Among them, the most commonly oils used for cooking are: palm, coconut, olive, sunflower, peanut, canola, corn and soybean oil. The extraction of the oil from the fruit or seed can be performed by using mechanical (oil press) and chemical (solvent extraction) systems.

The extra virgin olive oil obtained from the olive fruit is the unique oil extracted using exclusively mechanical and physical methods without any thermal or chemical treatment. Thus, it is the unique oil that can be consumed without being subjected to subsequent refining or other industrial process.

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Palmöl

Otherwise, all the other oils obtained from fruit or seeds (see above) are extracted using a combination of mechanical systems (extraction with presses) and chemical means, such as extraction with solvent. The most widely used solvent is hexane, a hydrocarbon resulting from the processing of petroleum products. Furthermore, the fruit and seed oils extracted using a combination of pressing and solvent extraction must undergo a process of refining that makes such oil edible.

The refining process involves treatment of the crude oil at high temperature and the use of chemical means. For example, one step of the refining process involves the treatment of the crude oil with a caustic soda (sodium hydroxide or potassium) solution to reduce the free fatty acid content to a final value of 0.05%.

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Desodorierung Turm von Palmöl Raffinerie 

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Sonnenblumenöl Desodorierung Turm

Furthermore, in order to remove the impurities, such as gums and pigments, which would “impair” the color of the oil, the degumming is accomplished by means of phosphoric acid. Even, the deodorization of the oil is performed in order to remove the volatile substances, which would “impair” the taste of the oil. Temperatures used in a deodorizing steam column reach upwards of 200° C.  

As such, refining process has as a primary consequence the decrease of the nutritional quality of the oils, since it lead to the complete destruction of thermolabile substances with high nutritional proprieties (naturally present in the oil), such as vitamins and antioxidant phenolic compounds. In view of this, it is easy to understand why the extra virgin olive oil has higher nutritional quality than all the other vegetable oils. In fact, the extra virgin olive oil is the unique oil which does not undergo to refining process.

For this reason, it possess high content of vitamin E and phenolic compound with valuable healthy activities. Additionally, the high content of phenolic substances with an antioxidant action together to the low content of polyunsaturated fatty acids, confer at the extra virgin olive oil higher stability toward the oxidation respect all the other vegetable oils. It is noteworthy to underline that during the oil oxidation, harmful and toxic substances can be originated. 

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[1] Vegetable oils in food technology: composition, properties and uses. Frank D. Gunstone Editor, Bluckwell Publishing, 2011 CRC Press (Roca Baton, USA)

[2] M.G. Lindley. The impact of food processing on antioxidants in vegetable oils, fruits and vegetables. Trends in Food Science & Technology, Volume 9, Issues 8–9, 1998, Pages 336–340.

[3] K. Franke, U. Strijowski, G. Fleck, F. Pudel. Influence of chemical refining process and oil type on bound 3-chloro-1,2-propanediol contents in palm oil and rapeseed oil. LWT - Food Science and Technology, Volume 42, Issue 10, December 2009, Pages 1751–1754

[4] Olive Oil: Chemistry and Technology,Dimitrios Boskou Editor, 2015, Elsevier (NL)

[5] Manuale degli oli e dei grassi. Capella P., Fedeli E, Bonaga G. Lercker G. Tecniche Nuove, 1997

[6] Pflanzenöle (pflanzliche Öle) sind aus Ölpflanzen gewonnene Fette und fette Öle