Olive Oil and Frying

The temperature that is reached inside the interior of food being cooked or fried, remains basically constant at 100⁰C, until the humidity that it contains has completely evaporated. Only then will the heated oil infiltrate the food being cooked.  Heated oil affects food only for a small time interval and for this reason only can we assume that frying is not that more damaging, and in many cases even less damaging, when compared to other methods of cooking.

The presence of atmospheric oxygen and high temperatures both maximize the self-oxidation of olive oil.  Oxidation will depend on the percentage of unsaturated fatty acids and oxidation promoting substances present.  Undoubtedly, oxidative activity will be limited by the presence of antioxidative substances.

Even if the percentage of unsaturated fatty acids in animal fats is very low, animal fats self-oxidize very quickly.  This is so because they do not contain any antioxidative substances.  Seed-oils also self-oxidize very quickly because, even if they contain large quantities of antioxidative substances [tocopherols], the portion of their unsaturated fatty acids is very high.  Olive oil on the other hand is very constant when exposed to atmospheric oxygen because, beyond its mediocre consistence of unsaturated fatty acids, it contains a great amount of antioxidative substances [tocopherols, polyphenols].

Olive oil, contrary to what happens in seed-oils, remains constant even in high temperatures [frying], because of its abundance in antioxidative substances and oleic acid.  The polyunsaturated fatty acids are those that are generally altered by thermal oxidation [exposure to intense heat].  This sensitivity is proportional to the oil’s average degree of unsaturation, and as to the number of double bonds in the simple chain of the fatty acids.  The significance being that in comparison with a saturated fatty acid [no free bonds] that has a very low degree of unsaturation [rated at 1], a monounsaturated fatty acid [one free bond] is rated at 10, while a polyunsaturated fatty acid [with two free bonds or three free bonds] is rated at 100 and 10.000, respectively.

Apart from the degree of unsaturation, the extent of alterations that are presented in fats and oils is proportional to temperature, duration of exposure and type of food that is being fried.

The by-products of heating fats or oils at high temperatures are peroxides, aldehydes, ketones, hydro peroxides, and various monomers.  Anyone of these compounds can have a toxic reaction if absorbed by the body.  They may attack the stomach, liver, cardiac and circulatory systems, kidneys and growth rate of the body.  They evidently affect the nutritional value of the cooked food.