“…Phenolic compounds are substances produced by plants, and as such are present in many of the foods we eat. In plants, they can serve as a sort of protection against insects or other pests, and they also add color or flavor to the plants. And when we humans eat plants, we reap the benefits of the phenols’ antioxidant properties, which have been associated with reducing the risks of certain diseases.
To determine the superiority of frying, the researchers cooked potato, tomato, eggplant, and pumpkin using four different methods: deep frying, sautéing, boiling in water, and boiling in a water-and-oil mixture. Then, the cooked vegetables were analyzed for fat content, moisture, and total phenols. Deep frying and sautéing in extra virgin olive oil, as you might expect, increased the fat content, but the total phenolic compound levels also increased, while the boiled vegetables either had very similar or lower phenolic compound levels when compared to the raw veggies.
The higher level of antioxidants comes from the extra virgin olive oil, which has its own phenolic compounds that are transferred to the vegetables during the cooking process. Don’t replace all the water in your soup with oil yet, though. “Boiling is recommended if the vegetables are to be consumed together with the cooking medium (i.e. the water),” Cristina Samaniego Sánchez, one of the study authors, says in a press release.” Lindsey Kratochwill Popular Science
The conclusion is that presence of extra virgin olive oil in cooking will increase the phenolics identified in the raw foods as oleuropein, pinoresinol, hydroxytyrosol and tyrosol, and the contents of vegetable phenolics such as chlorogenic acid and rutin.
Having said all that I feel obliged to mention, one of the author of this study Cristina Samaniego Sánchez admitted that while frying in extra virgin olive oil will increase the overall amount of phenols in vegetable more than any other cooking method, it also increased the calories and fat of the food. So, there’s that. Nevertheless, if you love frying you food, use extra virgin olive oil, this is one more prove that olive oil is far the best oil that you can use.
Source: University of Granada