Introduction fats an oils

 

 

 

In the past several decades, fats and oils have repeatedly received negative publicity and gained a reputation as being fattening. This bad reputation is certainly not unfounded; indeed, fats and oils supply approximately twice the amount of energy compared with carbohydrates and protein. Of course, the average German consumes too much fat each day. Contrary to the recommendation of the German Nutrition Society, more than 30% of our daily energy is supplied by fats.

With a daily intake of 2000 kcal about 70 g of fat are allowed. The amount actually consumed amounts to 130–150 g per day. With such excessive consumption, the bad reputation is pre-programmed. A result is that a great many low-fat diets recommend sharply reducing one's fat intake.

In view of the fact that too much fat is consumed, this recommendation is not wrong in principle. However, many of these diets do not take into account that fat not only supplies energy, but also essential (vital) components. Nevertheless, fats differ greatly in quality. Some supply more important substances, some fewer.

In a balanced diet, it is not only a matter of not continuously exceeding the recommended intake of 30%; choosing the right fats is also important, because in the proper amount and the correct composition, fats are clearly better than their reputation.

Origin, Area of Cultivation

Fats and oils can come from animals as well as from plants. Whether one speaks of a fat or an oil depends on its state at room temperature. Fats are solid at room temperature, oils are fluid. They are obtained by extraction, pressing or rendering.

Appearance, Flavour, Characteristics

Colours, flavours and uses of fats and oils are quite varied. More about this can be found in the descriptions of the individual oils.

Composition

Fats supply not only energy but also numerous substances such as vitamins, pigments, waxes, aromatic substances and fatty acids. Here we will deal with the fatty acids in more detail.

Generally, a differentiation is made between saturated and unsaturated fatty acids. The unsaturated are further divided into mono- and polyunsaturated fatty acids. This distinction is based on the chemical composition of each type.

Fats and oils are composed mainly of triglycerides, in which one molecule of glycerine is always esterified (combined) with three fatty acids. The fatty acids each consist of a chain of carbon atoms to which hydrogen atoms are added. When the maximal number of hydrogen atoms bind with the carbon atoms we speak of a saturated fatty acid. If one pair of hydrogen atoms is missing we have a monounsaturated fatty acid. If two pairs are missing we speak of a double unsaturated fatty acid, and so on. In general, fatty acids with at least two missing hydrogen atom pairs are known as polyunsaturated fatty acids.

Wherever no hydrogen attaches to the carbon atoms, these form a double bond. The fatty acids can be further subdivided according to the site of the double bond. If it is between the third and fourth carbon atoms it is termed an omega-3 fatty acid. Those with the double bond between the sixth and seventh carbon atoms are the so-called omega-6 fatty acids.

The length of the carbon chain and the degree of saturation determine the consistency and the melting point of a given fat. If a fat contains many saturated fatty acids it is solid; if there are more unsaturated fatty acids it is softer. But even solid fats still contain a certain amount of liquid fat (oil).

As a rule, animal fats contain more saturated fatty acids than vegetable fats do. However, there are exceptions: fish oil, for example, is rich in unsaturated fatty acids.

Below is a list of some important fatty acids, grouped according to saturation.

Saturated fatty acids

Monounsaturated fatty acids

Polyunsaturated fatty acids

Butyric acid

Palmitoleic acid

Linoleic acid

Caprylic acid

Oleic acid

Alpha-(α)-linoleic acid

Lauric acid

Eicosenic acid

Arachidonic acid

Margaric acid

Vaccenic acid

Eicosapentaenoic acid

Myristic acid

Icosenic acid

Docosapentaenoic acid

Palmitic acid

Cetoleic acid

 

Stearic acid

Erucic acid

 

Arachin acid

 

 



Some of these fatty acids will be explained in more detail under "Presumed Effects on Health".

Some substances that accompany fat have already been mentioned. For instance, fat is a vehicle for the fat-soluble vitamins A, D and E, which are involved in many important bodily functions. But vitamin E, for example, is important in fat itself: it is a natural antioxidant and keeps fat from becoming rancid. Vitamins A and D occur mainly in animal fat, vitamin E mostly in vegetable fat.

Also contained mainly in animal fat is cholesterol, which belongs to the sterines. It is frequently mistakenly assumed that vegetable fats and oils contain no cholesterol at all. This is true for many fats, but a few vegetable fats also contain cholesterol. The concentration is simply much smaller than in animal fat. Cholesterol is used in the body to produce bile acids and some hormones. Intake via fats is not necessary, however, as the body produces the required amounts itself.

One of the vegetable sterines is phytosterol, which is added to some foods as a functional substance, e.g. in cholesterol-lowering margarine.

Also found in fat are aroma substances. For this reason fat is also used in the food industry as an aroma carrier.

Harmful Substances

Some fatty acids are less beneficial for the body, some more. Among the less beneficial are lauric acid, myristic acid and palmitic acid. All three are saturated fatty acids and cause an increase in the concentration of cholesterol in the blood plasma, particularly of the unfavourable LDL-cholesterol.

Trans fatty acids, which are formed in the process of hardening fat, are detrimental to the blood cholesterol level in that they increase the LDL-cholesterol and lower the HDL-cholesterol. LDL is a fraction of cholesterol with an unfavourable effect that is connected with – among other things – the development of arteriosclerosis.

Quality Criteria, Optimal Storage Conditions

Oils are graded by quality according to the way they have been processed. Only those edible oils may be termed 'virgin' which have been won without the use of heat. However, they may be partially refined. Virgin oils that have been treated with steam for the sole purpose of improving their shelf life may be labelled additionally as 'unrefined'. 'Cold-pressed' oils and those 'from the first pressing' are won in a particularly gentle process. Specific information about processing and the term 'refinement' can be found under "Forms of Consumption, Use, Further Processing, Practical Tips for Preparation".

Fats are sensitive to light, heat, oxygen and extraneous odours. Therefore, these tips on storage should be followed: Unopened bottles of edible oil are best kept cool and in the dark. Oil in an opened bottle quickly becomes rancid. Close the bottle as tightly as possible and use it up as soon as you can. Butter and margarine, fats that contain water, should be kept in the refrigerator, as should cold-pressed oils with a high polyunsaturated fat content.

Presumed Effects on Health Regarding an optimal intake of fat, there are many recommendations, based on – among other things – the results of many epidemiological studies. These studies give reasons for the assumption that a regular intake of fats with a balanced fatty acid composition has a positive influence on the development of cardiac diseases.

The following recommendations are made with regard to fat intake:
Make sure that the intake of saturated fatty acids accounts for no more than one third of your total fat intake, because they increase the concentration of cholesterol in plasma. The other two thirds should consist of mono- and polyunsaturated fatty acids, whereby the monounsaturated should exceed the polyunsaturated.

The intake of essential fatty acids is particularly significant because they have two important functions in the human body: They form a component of the cell membrane, and they can be converted into eicosanoids, which are important for blood pressure, cholesterol and cell growth. α-Linoleic acid is one such essential fatty acid, which can be converted to eicosapentaenoic acid, but only when there is not an excess of linoleic acid at the same time. Recommended is an intake in the ratio of 5:1 (linoleic acid : α-linoleic acid). Eicosapentaenoic acid is one of the omega-3-fatty acids and is presumed to protect against heart attacks, among other things.

In contrast to many saturated fatty acids, both oleic acid and linoleic acid lower the concentration of cholesterol in the blood.

Forms of Consumption, Use, Further Processing, Practical Tips for Preparation

Vegetable oils and fats are obtained from fruits and seeds by extraction or pressing. Prior to extraction or pressing, the raw materials are processed so that the cells will break down and the oil will be easier to obtain. Fruits and seeds are cleaned and crushed for this purpose, and then roasted or steamed.

Pressing results in raw vegetable oil and the press cake, extraction in oil and extraction meal. In most cases, the raw oil is processed further. The processing of the oil comprises several steps which are summarized under the term 'refinement'.

Raw oil is seldom sold because it frequently has a rough, pungent taste and appears cloudy. To obtain a clear oil, phosphoric acid is added, which binds the cloudy and slimy substances. These can then be filtered out in a process known as desliming.

A further processing step is deacidification, by which free fatty acids, that are responsible for the rough taste, are bound with soda lye. Bleaching minimizes the portion of natural pigments. To this end, the oil is mixed with fuller's earth and heated to 70–90°C.

Finally, unwanted taste and aroma substances are removed from the fat in a vacuum, a process called deodorization.

Today, a combined process is also frequently used which is more gentle for the oil. It is known as physical refinement. By this method, two steps are combined and carried out together, desliming with (pre)bleaching and deacidification with deodorization.The benefits of such processing are clear: refined oils keep longer, are neutral in odour and are lighter in colour.

To make spreadable fat from fluid oils, two different processes are available, interesterification and hydrogenation. The latter has been known for around 100 years. By hydrogenation unsaturated fatty acids are converted into saturated fatty acids. A disadvantage of this method of hardening fat is that with partial hydrogenation trans fatty acids are formed.

Interesterification is used more frequently today. The conversion of oil to fat results from a targeted exchange of the different fatty acids of a triglyceride; this causes a change in the physical characteristics of the oil.

To obtain animal fats and oils, the fatty tissue of the given animal is heated to 80–120°C for about 20 minutes. The fat melts out. In contrast to vegetable fats and oils, animal fats may not be refined; only filtering off of the remaining greaves, or cracklings, is allowed.

Fats and oils are used for the preparation of both cold and hot dishes. However, not all fats are equally suitable. Cooking oils are used to prepare salad dressings and mayonnaise. According to taste and the respective dish, oil with either a neutral flavour or an intensive flavour can be used.
Nearly all fats and oils are suitable for cooking and baking. One should be careful in choosing a fat for frying, however. It should withstand temperatures up to 180°C. It should never smoke during the frying. Practically all cooking fats are suited to frying, but also some oils.

For deep-frying it is recommended to use only fats labelled as suitable. Special deep-fry fats are often a mixture of several different fats.

 



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