Which Fats Should We Use for Frying?

Fats are an essential component of the daily diet and should make up 20–35% of the daily energy requirement. Fats for frying should be chosen based on the smoke point temperature, where fats undergo many physical changes, such as oxidation, leading to their degradation. The fat is then broken down into glycerol and free fatty acids and at the same time loses its own nutritional value. The intensity of these changes depends on the temperature reached, cooking time, and the type and quality of the fat subjected to thermal processing. During this process, harmful substances like peroxides, aldehydes, and ketones are formed. Frying can have an adverse effect on the digestive system because it reduces the digestibility and absorption of fats. In addition, the oxidation products of fats that are formed during heating to high temperatures can have a mutagenic and carcinogenic effect on our body. Fats with a high proportion of saturated fatty acids are more heat-resistant than those with a high proportion of polyunsaturated fatty acids. Animal fats are rich in saturated fatty acids, while vegetable fats are more susceptible to oxidation, especially those that are rich in polyunsaturated fatty acids. Refining vegetable oils improves their heat resistance.

Butter is a well-known product made exclusively from cow's milk. It belongs to the group of high-fat products, and as an animal product it mainly supplies saturated fatty acids. It is rich in vitamins A, D and E and in macro and micro ingredients, including phospholipids. It also contains cholesterol. It is not recommended to use butter for cooking, mainly because the substances in it decompose very quickly during heat treatment. Excessive consumption of butter can also have a negative impact on lipid metabolism, which is harmful to the heart and circulatory system.

Sunflower oil is not suitable for frying due to its low smoke point (100°C for the unrefined variant). Its main components are polyunsaturated fatty acids such as linoleic acid and monounsaturated fatty acids such as oleic acid. Linoleic acid is more prone to oxidation than oleic acid. Sunflower oil contains about 55–66% linoleic acid. It can be used as a salad additive but should be stored in the refrigerator to slow down the oxidation process.

Olive oil is a product composed of 99% lipids. It is characterized by a high content of oleic acid (68%) which belongs to monounsaturated fatty acids. In comparison, there is about 57% in rapeseed oil. These acids play a particular role in the prevention of cardiovascular disease as they inhibit the development of atherosclerosis and reduce blood cholesterol levels. The remaining part of the lipids in the oil consists of saturated fatty acid (palmitic acid and stearic acid) – about 17%, and linoleic acid, which makes up about 8% of the lipid mass of olive oil. Due to its fat composition and content of antioxidants, olive oil is highly resistant to fat oxidation and is therefore excellent for frying. Olive oil from second pressing or refined exhibits even greater resistance to oxidation.

Corn germ oil is composed of vitamins, micronutrients and fatty acids. Similar to sunflower oil, it is rich in linoleic acid, making it unsuitable for frying. It can be mainly used in raw or refined form for frying. Furthermore, this type of oil should not be stored for a long time, especially in a very sunny place, because it quickly undergoes oxidation and digestion.

Flaxseed oil derived from seeds is obtained from the seeds of the flax plant. It primarily consists of linolenic acid (43.945%), to a lesser extent of linoleic acid (16.517,9%) and oleic acid (26,27%). Due to its high content of polyunsaturated fatty acids, this oil is not suitable for use in any heat treatment. To exhibit a positive impact on the cardiovascular system, it should be cold-pressed. Due to its high content of unsaturated fatty acids, it cannot be stored for long periods. Flaxseed oil derived from seeds should be stored in a dark container, in a cool, shaded location.

It is crucial first to distinguish between natural palm oil, which is hard even at room temperature, and its commercial version, oxidized by high temperatures and hydrogen to a liquid state. The latter form is harmful to the human body. Natural palm oil is useful for cooking by means of frying, as it is resistant to temperatures up to 200°C. Additionally, it contains a considerable amount of antioxidants, tocopherols and carotenoids (which quench oxygen radicals) and vitamins E and A. The best form of palm oil is red palm oil, consisting of 44% palmitic acid and 39% oleic acid.