Cooking Oils

By Dr Harold Gunatillake FRCS. FIACS., FICS., AM (Sing)
Cosmetic Surgeon, Oasis Private Hospital

Once upon a time, we had invariably, coconut oil on our kitchen rack, as all-purpose cooking oil. Then, life was simple, so was the choice of edible cooking oils. Cooking with butter, or margarine, to add more taste and flavor, was reserved for special occasions. Today, our housewives visiting the super markets; grocery stores have a most expanding choice of oils to choose from. Add to this there are varieties of cooking methods, boiling, stir frying, deep frying, sautéing, steaming, browning, baking, micro waving, and so on. Most cook books address cooking techniques, but do not mention, however, the harm these different cooking methods do to the nutrient value of the food items.

Then there is the problem of partial hydrogenation, to preserve the shelf life of these edible oils. Full hydrogenation of oils converts them into solid products, like margarine, whilst partial hydrogenation makes them semi-liquid. Most partially hydrogenated polyunsaturated vegetable oils on the shelves, omit this ‘damaging' word on the product's ingredient list on the label, and that too makes matters more difficult. Semi hydrogenated oils are as bad as the saturated fats for heart health. They have numerous adverse effects including increase of bad cholesterol, increasing the risk of diabetes, lowering the immune system, among others.

Partially hydrogenated oils are abundant in packaged refined foods of all types, as well as margarine, shortening, and bottled salad oils and dressings. Note that the open deep freezer that attracts you, at the center of any supermarket is packed with this sort of packaged foods.

Whatever reputation natural fats have earned, they are not the evil that some purport it to be. Fat is a nutrient, and is essential for the intake of fat-soluble vitamins like A, D, and E. It keeps our skin smooth and healthy. Fats are required for the manufacture of hormones in the body. Fat in food helps satisfy hunger by making you feel full after, because fat takes longer to leave your stomach than carbohydrates.

Canola, Sesame, varieties of olive oils, Corn, Safflower, Sunflower, are the common unsaturated vegetable oils from fruits, and seeds, that are readily available in the food stores, not mentioning our own home grown coconut which is mainly a saturated oil. As mentioned, unlike the saturated oils, the unsaturated ones need to be partially hydrogenated to preserve the shelf life, and prevent rancidity. In addition, all oils available in the supermarkets are refined losing specific nutrient values of the products.

Extraction of oil from seeds is through mechanical bulk extraction through a screw press. This is bound to destroy about 15% of the oil in the seed, depending on how powerful the pressing is. These press method of extraction do not protect the oil from light or oxygen.

These oils become rancid through a process of oxidation in no time. This does not apply to saturated oils like coconut, due to their stability against oxidation, and they are kept in the refrigerator for at least a year. On the other hand, the screw pressed unsaturated oils become rancid, and they are sold as ‘unrefined oil' in health food stores. From a nutritional angle they maintain their nutrient values for a short while. To get the other 15% oil from the seed, companies use petroleum solvents. To remove these carcinogenic solvents the oils are heated to about 150 C.

The next step these oils are subjected to is a process of ‘degumming'. This process removes phospho-lipids, including lecithin. It also removes iron, copper, calcium, magnesium, and other minerals.

Then mixing with the base sodium hydroxide removes further minerals and phospholipids.

Bleaching, the next process removes the beta-carotene an essential anti-oxidant that produces vitamin A. The temperature, which is subjected to this process, is about 110 C, the threshold at which fatty acids begin to become altered.

Deodorizing, being the next step, removes the aromatic oils and any remaining free fatty acids.

By the time these vegetable oils completes these processes, the oil is odorless, tasteless, and has no natural vitamins or minerals. The high temperatures these oils are subjected to severely damage the nutrients. It is really white oil.

The bright labels on the bottle would visibly emphasis ‘no cholesterol', a catchy word, and provide the various percentages of unsaturated, saturated oils with in, and also any vitamins, and minerals added.

Fats and oils are either mainly saturated like animal fats, and coconut oil, or unsaturated, can be either monounsaturated, like olive oil, canola oil, avocado, peanut oil, or polyunsaturated like safflower, corn and Soya. On reading the labels, one would notice that no oil is completely made of one fat only, they all are a combination of the three fats in different percentages, based on the nut, seed, or fruit from which the oil is derived.

Each of these oils, saturated or unsaturated, has its place in the kitchen and serves a specific function. Understanding which oil is suited for which use will help you to make the best choices. For health reasons it is best to avoid animal saturated fats, such as lard (pig fat), tallow (meat fat), and butter, at all times, except for very special occasions, because they increase the bad cholesterol. Coconut oil, though a natural plant saturated fat, does not increase the bad cholesterol in the blood, and is a suitable choice for all types of Asian cooking.

When it comes to Asian curry recipes, coconut oil would be the choice, for frying, temporizing, deep-frying, stir-frying, among other ways, for the Asian palate. When cooking other ethnic dishes, coconut oil may not be the right choice. Which type of oil, then should you use for cooking? Olive? Safflower, Sunflower? Remember that all oils have about 120 calories per tablespoon, and too much oil in daily use can lead to obesity.

Use a non-stick pan to fry meat, so that a very small quantity of oil may be used. One tablespoonful of oil may suffice cooking for four people.

Oils high in mono unsaturated oils – such as olive oil or canola oil- may actually be beneficial for the heart and arteries. If you suffer from heart disease these oils would be the smart choice. Corn, safflower and sunflower oils are high in polyunsaturated fats, and because of the high Omega 6 fatty acids content- (Linoleic acid), should be used sparingly. You may boost your Omega 3 fatty acid intake (Alpha Linolenic Acid), by using walnut oil. Omega 3 oils are important to maintain a healthy cardiovascular system.

If you are thinking in terms of flavors, choose stronger oil such as sesame, peanut or walnut. They are best used in salads instead of cooking, since their smoke point is low. Peanut and walnut oil also give a mild, nutty flavour to salad dressings.

If you are searching for a cooking oil to fry foods, choose one that wont burn quickly, having a high smoke point. Corn, safflower and soya oils are excellent choices. When foods are fried, including rice, they absorb quite a bit of the oil they are cooked in and therefore are much higher in calories and fat.

Heating cooking oils to their smoke point can cause serious indoor air pollution. Oxidation of the oil that occurs due to over heating liberates free radicals that are harmful for your health. Repeated usage of heated oil, except olive, also liberates harmful free radicals. A kitchen stove hood/vent, with a built in exhaust fan, is a very good idea to help reduce this form of indoor air pollution in the home.

Another really good way to reduce smoke from burning cooking oil is to choose your oils carefully, so you cook with oils that can handle high heat without smoking. Avacado oil has a smoking point of 500F. Unrefined canola oil, unrefined flaxseed oil, unrefined safflower and sunflower oils have smoke points below 225F. So these latter oils will be suitable for boil, steam, scald, stew, simmer, steep, parboil, and salad dressings.

Many Chinese cooks have a preference for peanut oil, especially for frying, because it has a pleasant flavor, it burns (smoke point) only at very high temperature (about 500F), and does not take on odours and tastes from foods readily as other oils. It is as high in mono-unsaturates as olive oil. The commercial super market brands are virtually tasteless, as most refined oils, which is fine for deep-frying, but, for tasty stir-frying choose expeller-pressed peanut oil. A good cold-pressed Asian peanut oil should have the fragrance of freshly roasted peanuts, just as good extra-virgin olive oil is redolent with olive aroma and flavour.

Unrefined corn oil, unrefined olive oil, semi-refined safflower oil, unrefined soy oil, unrefined Oleic sunflower and unrefined walnut oils have a smoke point below 320F.

These oils are suitable for low heat baking, light sauté, pressure-cooking.

As mentioned Avocado oil has a smoke point below 500F. This is suitable for Sear, brown, and deep fry.

Some oils should never be heated. These oils, found on the supermarket shelves in the nutritional supplement category in the refrigerator, can also be used as condiments. Use them in dips, and dressings, or add to a dish after it has been removed from heat. A good example is walnut oil. Add it on to your salad to get that nutty flavour. Add sesame oil to your stir- fry after cooking to add extra flavour. To add essential fatty acids to your diet, use flax, evening primrose, borage, black currant and wheat germ oil, to your cooked food when cooled.

All oils should be kept in the refrigerator, after being opened, to preserve the nutritional value of culinary oils. Oils may thicken, but if you let them stand at room temperature they'll soon return to liquid. Some oils should be protected from heat and light too, such as olive oil, flax, walnut, and pumpkin oils. Store them in a dark cool pantry. Exposures of oils to oxygen, leads to rancidity, hence close tight with the lid after use. Rancid oil has an unpleasant aroma and acid taste, and its nutrients are greatly diminished. The unsaturation in fatty acid chains are unstable and are vulnerable to attack by oxygen, especially if fats are heated in the presence of air or left standing exposed to air. The products resulting from these oxidation reactions are highly reactive molecules that damage DNA and other vital components of cells, states Dr Andrew Weil in his book “Natural Health, Natural Medicine (Houghton Mifflin Co. Boston, 1990). Diets high in polyunsaturates increase the risk of cancer, speed up aging and degeneration of tissues, and may aggravate inflammatory disease and immune system disorders. It has been shown that only the oils found in olives and nuts help protect against breast cancer whilst those found in soya, sunflower and maize increases it, the Swedish study claimed.

Extra virgin and virgin olive oils keep about a year after opening. Most polyunsaturated oils keep well up to eight months; unrefined polyunsaturated oils half as long.

Often in cooking, the ethnic character of the dish you're preparing offers a clue to which oil is most suitable. When you think of garlic, tomatoes, eggplant, for instance a fully flavoured fruity olive or fruity coconut oil comes immediately to mind. When you think of a Chinese dish with ginger, soy sauce, peanut oil would be the choice.

Olive oil and canola oil have been recommended as the safest sources of fat in a heart-healthy diet. But some people claim that canola is hazardous to health. The controversy apparently stems from the fact that the oil comes from rapeseed, a mustard family member that was once deemed unsafe due to unhealthy amounts of erucic acid in the plant. The problem was resolved when a new crop, canola with very low levels of erucic acid was developed from rapeseed in Canada in the mid-1970s.

The whole subject of healthy oils becomes more and more complicated as time goes on. Hence use very little oil in your cooking. Good oils are not cheap, and deep- frying takes more than you would normally use and such used oil must be discarded after one use. Deep- frying should never be a daily treat, but should be occasional. Polyunsaturated fats were recommended against saturated fats when doctors became aware of dangers of saturated fats. Now we know that polyunsaturated fats have dangers of their own.

Ultimately, our choices of choosing cooking oils are restricted from a health angle, but from a culinary angle the choices are variable.

Coconut has stood the test of time in Asian cooking. It is cheaper, produced in our own little island, and should be our first choice for daily usage. Nutrients are contained in unrefined coconut oil, and it is advisable to refrain from purchasing the refined ‘white oil'. For other ethnic cooking the mono-unsaturates would be the choice, such as extra virgin olive oil, canola oil and peanut oil. Do not heat oils to the smoking point- the smoke can be carcinogenic. It could have an off flavour, lose its nutritional value, and also turn into a transfat laden heart disease machine. Do not reuse oil. Even though the oil may look all right, the more it is heated, the more oxidation, and therefore free radical damage, is caused. Therefore, oil should be discarded after each use.

When you deep-fry in a wok, or shallow-fry, you will be using smaller amounts of oil than you would when deep-frying in a electric deep-fryer.

Olive oil, however, beneficial health-wise should be restricted if you are on a diet to slim.

Coconut oil would be the choice, then.

My apologies for mentioning certain oils that is not available in our local food stores. It is hoped that they will be available in our markets in the near future, after all variety should be the spice of life.

Ref: How is Cooking Oil Processed? www.vegez.com
How to choose the best cooking oils by Lynn Grieger, R.D., C.D.E.

Smoke Point for Cooking Oils by Annie Berthold-Bond, Producer, Green Living Channels

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