If a grease is liquid at room temperature, it is called oil. In plants, fats and oils are usually found in their seeds or germs, in animals in fat tissue.
Fats and oils are used both as food (edible fats and oils) and in engineering (e.g. as lubricants). Fats and oils, as well as carbohydrates and proteins, belong to the basic nutrients of humans.
They are needed in the human body among other things as:
- Energy supplier (so-called reserve substance)
- Isolators against cold
- solvents for only fat-soluble substances such as some vitamins
- Protective pads for internal organs and the nervous system
- Component of cell membranes
Fats and oils – Recovery
Fats and oils are mainly obtained from animal products or from plants (useful plants).
Vegetable fats and oils used in food are derived from oil plants (e.g. Olives) or oilseeds (e.g. rape) are obtained by pressing or extraction with steam or solvents. Refining and thus removing undesirable ingredients makes the fats usable for humans.
Margarine was originally of animal origin, but is nowadays obtained by hydrogenation (fat hardening) of the carbon double bond(s) (see Figs. 3 and 4) in the fatty acid residues of vegetable oils (sunflower oil, rapeseed oil, etc.). Trans-fatty acids can form.
The physical properties of a fat (e.g. whether it is solid or liquid) are influenced by the chain length and especially by the frequency of carbon double bonds (see Figs. 3 and 4) in the fatty acid residues. Vegetable fats contain many unsaturated fatty acids and are therefore mostly present as oils. Natural fats are usually a mixture of different fatty acids and therefore do not have a melting point but a melting range.
The solid products contain high proportions of long and saturated fatty acids (see Fig. 3), whereas the fatty acids in the liquid oils are predominantly monounsaturated or polyunsaturated (see Fig. 4). When heated, some fats decompose below their boiling point. Fats and oils themselves are usually odourless and tasteless. However, they are highly valued in the kitchen as flavour carriers.
Fats and oils for energy storage
Fats and oils are, besides carbohydrates such as sugar, the most important energy store of our organism. The physiological calorific value of 9.3 Kcal/g fat is more than twice as high as that of carbohydrates and protein with 4.1 Kcal/g. As so-called “depot fat” they thus form a suitable storage form for energy – in humans the quantity for this is approx. 10 kg and more.
The depot fat in the human body comes from the fat ingested with food, but also from sugar and protein, which has been converted into fat. Other mammals can also make depot fats from an energy surplus in food (e.g. the bear with its “winter bacon”).
The density of human fat tissue is 0.94 kg/l, the physiological calorific value (energy content) is around 7,000 kcal/kg.
Saturated, unsaturated and trans fatty acids
Saturated Fatty Acids
There are no double bonds between the carbon atoms. An example of this is stearic acid (Fig.1).
Single unsaturated fatty acids
Have at least one double bond between the carbon atoms of the chain. An example of an unsaturated fatty acid is linolenic acid (Fig.2).
Multiunsaturated Fatty Acids
Have two or more double bonds between the carbon atoms of the chain.
Some unsaturated fatty acids are essential for humans because they cannot be synthesized by the human body.
These include fatty acids that carry double bonds at certain positions, so-called omega-n fatty acids. Here n stands for a number and describes the position of one of the double bonds (see Fig. 2).
In the omega counting method, counting starts at the end of the carbon chain (in the figure on the left). The double bond near the carboxyl group is therefore given the largest number (in the figure on the right). The figure for linolenic acid shows the omega counting method. Only the double bond counted first is decisive for the classification into the different groups of omega-n fatty acids. Linolenic acid is therefore a triple unsaturated omega-3 fatty acid.
In addition to unsaturated fatty acids, trans fatty acids also occur in nature. Trans-fatty acids are also a by-product of margarine production and are suspected of having harmful properties.
Fats and oils are perishable. In particular, they can change chemically through light, higher temperatures, atmospheric oxygen, water or microbes. As a rule, double bonds or ester bonds are affected by spoilage, whereby they become rancid and therefore toxic. Fats and oils are advantageously protected by cool, dry storage that is inaccessible to air.
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