Researchers from the University of Granada (UGR) have found that cooking in Extra Virgin Olive Oil (EVOO) increases the phenolic fraction present in many raw vegetables more than other methods.
In an article published in Food Chemistry magazine, researchers say vegetables fried in EVOO improved their antioxidant capacity and the amount of phenolic compounds, which prevent chronic degenerative pathologies such as cancer, diabetes or macular degeneration.
The aim of this research was to determine the effect of applying various cooking methods on the antioxidant capacity and the amount of phenolic compounds (total and individual concentrations) present in vegetables. Potato, pumpkin, tomato, and eggplant were sautéed in olive oil, boiled in water, or boiled in water and olive oil.
“Comparing the content of phenols with that of raw vegetables we found increases and reductions alike, depending on the chosen method. Oil as a mean of heat transfer increases the amount of phenolic compounds in vegetables, opposite to other cooking methods such as boiling, where heat transfer is done through the water”, explains one of the authors of this paper, professor Cristina Samaniego Sánchez from UGR.
This is due to a transfer of phenols including tyrosol, from EVOO to the vegetables, enhancing the latter with oil-exclusive phenolic compounds which are not naturally present in raw vegetables.
“Therefore, we can confirm that frying is the method that produces the greatest associated increases in the phenolic fraction, which means an improvement in the cooking process although it increases the energy density by means of the absorbed oil,” says Samaniego.
All the cooking methods increased the antioxidant capacity of all four vegetables. It was a reduction of it or an absence of significant changes after boiling them in water, in certain cases.
Samaniego stresses that each cooked vegetable developed a specific profile of phenols, moisture, fat, dry matter and antioxidant activity determined by the original characteristics of the raw vegetables and the cooking method applied.
“When the phenolic content of the raw vegetable is high, the total content of phenols is increased even more if EVOO is used in the process, and boiling doesn’t affect the final concentration. Therefore, we must stress that frying and sautéing conserve and enhance the phenolic composition. Hydrothermal cooking methods can be recommended when the food is consumed together with the cooking water, as the addition of EVOO improves the phenolic profile and compensates for the deficiencies of the raw food”, the researcher stresses.