Scientists already knew from various studies that, when heated to frying temperatures, some oils such as sunflower oil produce more toxic compounds than olive oil . Now researchers from the Innovation in Chemical Analysis group of the University of Jaén, in collaboration with the Laboratory of Bromatology and Hydrology of the Faculty of Pharmacy of the University of Porto, have shown that extra virgin olive oil resists the frying process better than other commercial varieties. After comparing it with other vegetable fats, experts have seen that the abundance of antioxidants in extra virgin olive oil is responsible for its degradation less and more slowly than the others .
It is also the most stable and produces the fewest toxic compounds. The oils used in the comparative research on the thermal oxidation process were extra virgin olive, the most used in Mediterranean countries; the peanut, typical of Portuguese school canteens; and canola, a type of rapeseed oil common in some Central and Eastern European countries . In the experiment, the researchers kept the oils hot for several hours during which they made several potato fries at different times. After each frying, they analyzed the resulting substances that could be harmful to health. In this way, they identified more than thirty toxic compounds resulting from heat stress derived from frying .
The study, published in the Journal of the American Oil Chemists’ Society , shows that the benefits of extra virgin olive oil compared to other oils used for frying come from its lower percentage of polyunsaturated fatty acids , such as omega 3, and a higher percentage of monounsaturated fatty acids, such as oleic (omega 9) , one of its main components. Despite the fact that all the fats studied contain few polyunsaturated fatty acids, extra virgin olive oil when frying produces fewer toxic compounds and takes longer to appear than in the case of peanuts and canola due to the high content of antioxidants. These are responsible for the olive degrade less and more slowly than the others.
In short, extra virgin olive oil is the most suitable for frying because it resists heat better and remains stable after several hours at high temperatures. Up to eight hours after being subjected to strong heating, toxic thermal oxidation products do not appear . In addition, the extra virgin olive preserves a good nutritional value and is more useful for the body.
Research has focused on the study of the nature and concentration of the compounds that are altered or appear during the frying process, especially those that can be harmful to human health, such as volatile aldehydes. In addition, the study offers detailed information on the volatile compounds that originate during frying as a consequence of the thermal degradation of oils, which helps to understand the chemical reactions that take place in the process. These substances are valid as quality indicators to control and ensure their nutritional value and shelf life.
