Vegetables fried in extra virgin olive oil have more beneficial properties than when boiled

Vegetables fried in extra virgin olive oil have more beneficial properties than when boiled


A new UGR study, published in the prestigious journal Food Chemistry, reveals that vegetables fried in extra virgin olive oil have more beneficial properties than their boiled counterparts.

The Mediterranean diet in Spain is characterized by a high intake of vegetables and extra virgin olive oil (EVOO), both of which are important sources of biofunctional compounds that have been linked to the prevention of chronic degenerative diseases, not only because they contain nutritive antioxidants such as vitamins C, E, and ß-carotenes, but also because they contain important amounts of non-nutritive antioxidants such as phenolic compounds. Phenols are found in EVOO and fresh vegetables typically consumed in Spain, such as aubergine, potato, tomato, and pumpkin, all of which have distinctive qualitative and quantitative compositions of phenols.

It is often thought that when we cook raw vegetables in certain ways and using certain cooking techniques, their antioxidant properties, such as the phenolic compounds, are to some degree lost or destroyed.

In order to determine whether there was any truth to this assumption, researchers at the UGR set out to test some of the most common ways we cook those vegetables that form an integral part of the Mediterranean diet.

The aim, therefore, was to put domestic cooking techniques to the test and determine how they affect and/or enhance the antioxidant qualities and amounts of phenolic compounds found in four fresh vegetables that are representative of the Mediterranean diet, namely; potato, pumpkin, aubergine and tomato.

Fried, boiled or mixed with water and extra virgin olive oil?

Three cooking techniques were employed: 120gm cubes of the vegetables were fried in EVOO, or boiled in water, or boiled in a mixture of water and EVOO. The experimental procedures were strictly controlled, with invariable proportions of the vegetables and the cooking mediums maintained throughout the analyses.

The vegetables were also kept in optimum conditions in order to accurately measure their moisture, fat, dry matter, and phenol contents, along with their antioxidant capacity, before and after each cooking method was employed.

A breakthrough in food science

In a new breakthrough in the field of nutrition and food science, the researchers found that frying vegetables in extra virgin olive oil produces higher levels of natural phenols, antioxidants that have been linked to the prevention of chronic degenerative diseases such as cancer, diabetes and macular degeneration (a disease which causes blindness).

Cristina Samaniego Sánchez, one of the authors of the work, explains: “While comparing the total phenol contents of the fresh vegetables, we found both increases and decreases in their levels, depending on the cooking method employed. As a heat transfer medium, the EVOO increases the amount of phenols in the vegetables, in contrast with other methods such as boiling, which use a water-based heat transfer medium.”

The results show that the overall quality of these vegetables is substantially improved when they are fried in extra virgin olive oil. This occurs because the vegetables are enriched with EVOO phenols transferred from the oil, which otherwise would not be present.

“We can conclude that frying in EVOO was the technique with the highest associated increases of phenols and can therefore be considered an improvement in the cooking process, although it also increases the calorie density of the food because of the amount of oil absorbed”, points out Samaniego.

“If the concentration of phenols found in the raw ingredients is high to start with, the overall concentration level is further increased if EVOO is employed during the cooking process, while boiling does not significantly affect the concentration levels. Boiling is recommended if the vegetables are to be consumed together with the cooking medium (i.e. the water).”

The research findings have significant implications for food science and nutrition, and may re-shape the way perceive so-called “healthy” and “unhealthy” ways of preparing the food we consume, while we simultaneously strive to stay within the limits of healthy calorie intakes.

You can read the full academic article here:

Article sources:

The results of this work are part of Jessica del Pilar Ramírez Anaya’s doctoral thesis, completed under the supervision of Cristina Samaniego Sánchez, Marina Villalón Mir, and Herminia López-García de la Serrana, at the UGR’s Nutrition and Food Science Department .

Ramírez Anaya, J. P., Samaniego-Sánchez, C., Castañeda-Saucedo, M. C., Villalón-Mir, M., López-García de la Serrana, H. (2015). Phenols and the antioxidant capacity of Mediterranean vegetables prepared with extra virgin olive oil using different domestic cooking techniques. FoodChemistry, 188, 43-438

Contact details (if you wish to contact the researchers):

Cristina Samaniego Sánchez

UGR’s Nutrition and Food Science Department

Phone: +34 958241000