Art of Diet

Which oil is the best for cooking, frying ?

Ms H 

In foods, fatty acids are mainly found in lipid complexes called triglycerides. Fatty acids are long aliphatic chains consisting of carbon and hydrogen atoms. The carbon chains vary in length, degree of unsaturation (number of double bonds between carbon atoms) and structure. So some fatty acids are saturated, while other have different degrees of unsaturation.

When you are frying or cooking at a high temperature (at or close to 180 ⁰C) the molecular structures of the fats and oils you are using change. They undergo oxidation, when we talk about lipid oxidation it is only the polyunsaturated fatty acids, which are of interest. Polyunsaturated fatty acids contain two or more double bonds, and it is these double bonds, which are prone to oxidation. Consequently, the risk of oxidation increases with the number of double bonds present in the fatty acid. 

The degradation of unsaturated fatty acids by oxidation is directly related to nutritional, flavour, safety and storage problems. There are two major oxidation reactions, which can occur in foods containing lipids; auto-oxidation and photo-oxidation. The auto-oxidation is the most common. Auto-oxidation occurs in the presence of oxygen. It is initiated when a hydrogen atom is abstracted in the presence of initiators such as light, heat, metals or oxygen, forming a lipid radical (a very reactive molecular part), which reacts with oxygen making a lipid peroxide radical (another reactive substance). These peroxide radicals react with a second lipid, yielding a lipid radical and a hydroxyperoxide. The hydroxyperoxides will be decomposed into secondary oxidation products. The products of secondary oxidation: reactive aldehydes, alcohols and ketones have negative health inferences due to their cytotoxic, mutagenic and neurotoxic action.  Lipid oxidation may also severely change the nutritional quality of foods by damaging vitamins and polyunsaturated fatty acids.

This chain of reactions may be staggered by antioxidants producing a combination of radical species to give non-radical and non-propagating species. Photo-oxidation occurs when norma triplet oxygen are converted to singlet oxygen by the exposure of UV radiation. The singlet oxygen interacts with polyunsaturated fatty acids to form hydroxyperoxide, which initiate the auto-oxidation reaction.

Prof Grootveld’s (De Montfort University in Leicester) team measured levels of “aldehydic lipid oxidation products” (LOPs), produced when oils were heated to varying temperatures. The tests suggested coconut oil produces the lowest levels of aldehydes, and three times more aldehydes were produced when heating corn oil and sunflower oil than butter.

Some advices

Try to do less frying, particularly at high temperature. If you are frying, minimise the amount of oil you use, and also take steps to remove the oil from the outside of the fried food, perhaps with a paper towel. To reduce aldehyde production go for an oil or fat high in monounsaturated or saturated lipids (greater than 70%), and low in polyunsaturated (less than 20%). Probably the olive oil is the compromised cooking oil but the antioxidant levels present in the extra virgin products are insufficient to protect us against heat-induced oxidation. Important: always keep your oils in a cupboard, out of the light, and try not to reuse them as this also leads to the accumulation of nasty side-products.

When you eat food such nuts, seeds, fish and leafy greens, they have clear health benefits, which   contain polyunsaturated fats. Monounsaturated fats are in avocados, olives, olive oil, almonds and hazelnuts, and also in lard and goose fat. Olive oil, which is approximately 76% monounsaturated, is a key component in the Mediterranean diet, which has been shown to reduce the risk of heart disease. The extra-virgin olive oil has its smoke point about 160-190 ⁰C so it is best for drizzling on salad and finishing soup and pasta. The refined olive oil smokes at 240 ⁰C so it is still not recommended for deep fry. Eating saturated fats, particularly dairy and other fats derived from animals, the benefits of doing so confronted. 

Coconut oil is on the top of the table. It is high in saturated fat; contains lauric acid, a medium chain saturated fatty acid with 6 carbon atoms in the molecule. It does raise cholesterol levels, mainly increases HDL, the healthy type of cholesterol. Coconut oil contains medium-chain triglycerides, which are used directly for energy by your body. All forms of coconut are high in calories and should be consumed in moderation. Avoid partially hydrogenated coconut oils, which are not natural and are associated with increased risk of numerous diseases.

Rapeseed oil has delicate, nutty flavour, is high in monounsaturated fats and it   has high level of vitamin E. When extra-virgin and cold-pressed, it is delicious in dressings and dips, as well as in baking, frying and general cooking.

Butter is the second best in the table for cooking. It is rich in the most easily absorbable form of Vitamin A and vitamin E, K and D. It also contains lauric acid, lecithin, essential for cholesterol metabolism, calcium, anti-oxidants that protect against free radical damage, conjugated linoleic acid, which is a potent anti-cancer agent and immunity booster.

Goose Fat is high in ‘heart healthy’ monounsaturated (55g compared to 19.8g in butter) and polyunsaturated (10.8g compared to 2.6g in butter) fats. Goose fat provides the body with the fat- soluble vitamins; vitamin A, vitamin E, vitamin D and vitamin K, which are essential for growth and fatty acids, which are significant in sustaining normal health and body functions. Goose Fat contains on average 58% oleic acid a specific type of monounsaturated fatty acid, which can lower blood cholesterol levels

In cooking, baking and frying you should vary the above mentioned oils; coconut oil, butter, goose fat and rapeseed oil.