Studies concerning the use of virgin olive oil during cooking and, in particular, in frying, are rich enough. In fact, the researchers’ considerable interest in these studies derives from the fact that the frying is one of the most common procedure for food preparation.
The complicated chemical-physical variations during frying lead to a reduction of nutritional oil level.
The oxidation of fats considerably speeds their process up at a high temperature and in the presence of the atmospheric oxygen. The intensity of the oxidation process is proportional to the degree of the unsaturation of the fat (oil) contained in mono and poly-unsaturated fatty acids, while its action is opposed by the presence of antioxidant substances: only olive oil responds in a stable way to the combined attack of oxygen and high temperatures. The size of fats alterations during cooking depends on other decisive factors: 1) Level of temperature; 2) Duration of cooking time.
The higher the temperature is, the easier it happens that there are fats alterations that can be responsible for toxic effects.
The degree of temperature that influences with deep modifications is defined as “smoke point” and it depends on its chemical composition; this level shall not be exceeded and it is good to remember that olive oil has the highest point among all oils. The duration of cooking time is more decisive than the thermal level during which after long periods there can be toxic effects with the formation of degradation products such as monomers and peroxides. Even in this case, olive oil possesses a degradation index substantially lower than other vegetable oils.
From these considerations it is evident that, in any case, frying causes more or less a fat deterioration: however, it is recommended to use an olive oil to have more satisfying results.