Oils - a significant part of our diet

Oils

Oils play a significant part in the diet of most of British people. Used in baking, for dressings, for sauteing and frying, their quaility and nutritional value is an important but easily overlooked issue. Oils should certainly be taken into consideration when considering a healthy diet.

Composition of oils

Oils are fats which are in liquid state when at room temperature. Fats and oils consist of molecules of glycerol plus three molecules of fatty acids. The chemical structure of the fatty acids determines whether it is saturated or unsaturated. 'Saturated' indicates the absence of double chemical bonds so that the molocules can not contain any more hydrogen atoms, i.e they are saturated with with hydrogen.

Oils are unsaturated and are further categorised into monosaturates e.g olive oil, and polyunsaturates e.g safflower oil, corn oil, sunflower oil and soya oil. Polyunsaturates contain the smallest number of hydrogen atoms.

Function of Oils

Fats are required in the diet as they provide the structural components of the cell walls of all tissues. They also act as carriers for the soluble vitamins A, D, E and K.

Whilst an excess of saturated fat in the diet can lead to raised cholesterol levels and heart-related diseases, polyunsaturated fats can actually lower cholesterol levels. Some oils contain essential fatty acids, a deficiency of which can lead to heart disease, acne and eczema. Mono-unsaturates too have actually been found to reduce cholesterol levels.

Extraction of Oils

Oil is liberated from the raw material by mechanical pressure (or in the case of refined oils, chemical solvents).

Where a product is soft, it is cold pressed, so keeping vitamin destruction to a minimum.

Other items of interest

Harder products such as safflower are expeller processed. Extraction rates from pressings are low and the oil has a higher nutritional value. It also retains its characteristic smell and taste.

Uses of Oils

The root of the word "oil" is "olive" and olive oil is arguably the finest of all oils.

Olive Oil

The strength of its flavour lends itself to use as a salad dressing (add a little lemon juice or vinegar for extra "tang"), or as a condiment with jacket potatoes, pizzas and hot vegetables. It can also be used in casseroles and sauces. Olive Oil is comparatively pricey, but this is not surprising when you consider that on average a tree produces 10 kilos of fruit and it takes 5 kilos of fruit to make 1 kilo of oil.

Corn Oil

Use in baking or in salads.

Sesame oil

A favourite in Far Eastern cookery. It is usually fairly pungent in flavour, so is best used in small quantities. A brilliant oil in for stir-frys and marinades.

Nut oils

Nut oils are becoming increasingly popular, and are particuarly good in salad dressing and hot or cold vegetable dishes. Almond oil is cheaper than hazelnut or walnut and is ideal for use in cakes and pastries. Macadamia Nut oil is highly recommended for cooking.

How to Choose your Oil

Commercial oils are highly processed, which means that much of the nutritional value is destroyed. Quality natural oils are only obtained by "cold pressing". This is a purely mechanical process, during which temperatures are maintained at a low level. There is no chemical or heat treatment.

Mechanical Pressing - Has an acidity of less than 1%. Likely to be the product of just one country or region. Flavour will be strong.

Extra Virgin First Pressed - This is the purest and finest oil and is extracted from the first pressing.

Extra Virgin Cold Pressed - Low pressure pressing. High quality.

Pure - Oil extracted from the third or fourth pressing and refined. The refining process includes washing with caustic soda, bleaching, fine filtering and deoderising at high temperatures. These processes can remove minerals and vitamin E which is a natural anti-oxidant and prevents rancidification.

Light - Least pressing. The mildest flavour.

General Comments

Exposure of oils to the atmosphere causes them to turn rancid. Apart from rendering the oil unpalatable, rancidity also destroys vitamins A, C, E and B6. Oil should therefore be kept in a cool place and customers should be advised to refrigerate after opening.

Oils should be cooked slowly and gently. If the oil begins to smoke, the composition of the oil changes and essential fatty acids are destroyed. Oils high in mono-unsaturated fats tend to be more stable when heated than polyunsaturates, making them more suitable for cooking - eg peanut, avocado, almond, olive and palm.