Deep frying is often regarded as an unhealthy cooking method. While this may be true for some food items, researchers found that deep frying veggies in olive oil releases compounds that may prevent cancer and other diseases.

Researchers from the University of Granada in Spain discovered that using Mediterranean extra virgin olive oil (EVOO) amps up antioxidant-containing phenolic compounds of vegetables. Meanwhile, other cooking methods lack this specific beneficial feature.

"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," says co-author Cristina Samaniego Sánchez.

Certain cooking methods are thought to remove healthy substances such as phenols found in vegetables. To test this theory, the scientists cooked 120 grams of potato, tomato, eggplant and pumpkin in three ways - deep frying in EVOO, boiling in water and lastly, boiling in a mixture of water and EVOO.

The researchers implemented strict control measures to maintain cooking mediums and to ensure that the vegetables are at its optimum conditions. They then analyzed the fat content, moisture, dry matter and level of phenols present in the vegetable samples.

The scientists found that vegetables fried in EVOO increased its phenolic contents. In fact, the vegetables had more phenols than when it was still raw. The authors said this is because EVOO already contains phenols. During the cooking process, these substances are transferred to the vegetables, thus adding up its phenolic value.

Boiling also increased the antioxidant properties of the vegetables however, the rise was not that significant.

Samaniego then concludes that frying vegetables in EVOO is the cooking method with the greatest association with increased phenolic compounds.

While the technique may improve cooking process, Samaniego says it may also increase the calorie density of food due to the amount of oil absorbed. The authors then recommend boiling if the veggies are to be eaten with the cooking medium such as water.

The study has relevant implications to nutrition and food science as the findings may shape people's perception of healthy and unhealthy cooking methods.

The study was published in Food Chemistry magazine.

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