Extra olive virgin oil is touted for its health benefits. A staple of the Mediterranean Diet, the oil contains antioxidants attributed to its phenolic compounds.
While in Mediterranean countries extra virgin olive oil is regularly used as a final seasoning, it is also used for roasting, sautéing, stir-frying and deep-frying.
There is a risk that such culinary techniques could diminish the minor components of extra virgin olive oil, such as polyphenols. This could occur through substances leaching into the food, or by degradation and transformation of the oil’s polyphenol content.
A team of researchers from the University of Barcelona and the University of São Paulo have sought to determine whether, in a domestic kitchen environment, extra virgin olive oil is degraded when applied to heat – and specifically, when pan-fried or sautéed.
"The effects of cooking on these polyphenols of oil have always been studied in a laboratory or industrial situation, which is far from the reality of our homes," noted director of the Institute in Research on Nutrition and Food Safety (INSA-UB) and study co-author Rosa M. Lamuela.
The thinking is that results from a domestic setting could be used to inform future recommendations or nutritional guidelines.
What is extra virgin olive oil?
Where regular olive oil is refined and stripped of important nutrients and antioxidants, extra virgin olive oil is produced using a natural extraction process – without the use of heat or chemicals.
This allows the oil to retain all the nutrients and antioxidants from the olive fruit. As a result, extra virgin olive oil is regarded the highest quality olive oil available.
Extra virgin olive oil is the main source of fat in a Mediterranean diet. It displays a singular fatty acid composition with a higher content of phenolic compounds and other antioxidants than other edible oils.
Its consumption has been demonstrated to play a protective role against diseases such as cancer, cardiovascular diseases, diabetes, and neurodegeneration.
Extra virgin olive oil in a domestic kitchen
In the study, published in academic journal Antioxidants, the researchers simulated the cooking conditions of a domestic kitchen. The aim was to determine how homemade sautéing affects the polyphenols of extra virgin olive oil.
The effects of time – whether the oil was sautéed for a long or short period – and temperature (at 120°C and 170°C) on the degradation of antioxidants was also analysed.
Results revealed that temperature did have a degrading effect on the polyphenols of extra virgin olive oil during the sauté cooking process. At 120°C, the content of polyphenols decreased by 40% and at 170°C, it decreased by 75% – compared to the levels of antioxidants in raw oil.
Time had an effect on such individual phenols, such as hydroxytyrosol, but not on the total phenol content.
Overall, antioxidant levels remained with the ‘healthy range’, as stated in European regulation.
"Despite the decrease in concentration of polyphenols during the cooking process, this oil has a polyphenol level that reaches the declaration of health in accordance to the European regulation, which means it has properties that protect oxidation of LDL cholesterol particles," noted co-author Julián Lozano.
What do these findings mean for the Mediterranean diet?
The Mediterranean diet varies from country and region but is largely based on consumption habits of those living in countries bordering the Mediterranean Sea, including Greece, Italy, Spain and France.
Broadly speaking, the diet champions vegetables, fruits, legumes, nuts, beans, cereals, grains, fish and unsaturated fats such as olive oil.
However, the health benefits experienced by those living near the Mediterranean and eating these locally sourced ingredients, are not always transposed to people following the diet in other geographies.
According to the researchers, this is likely due to cooking practices. These latest findings are expected to support the idea that Mediterranean cuisine is beneficial for health – not purely for the ingredients themselves, but for the ways of cooking it.
Thus, it would be beneficial to analyse the effects of cooking extra virgin olive other with other food elements from the Mediterranean diet. "Moreover, we should conduct random research studies in humans, in which we would compare the potential benefits we obtain when cooking with quality extra virgin olive oil compared to other oils," noted Lozano.
‘Domestic Sautéing with EVOO: Change in the Phenolic Profile
Published 16 January 2020
Authors: Julián Lozano-Castellón, Anna Vallverdú-Queralt, José Fernando Rinaldi de Alvarenga, Montserrat Illán, Xavier Torrado-Prat, and Rosa Maria Lamuela-Raventós