Fats and Oils
organic compounds; complete esters of glycerol (triglycerides) and monobasic fatty acids. They belong to the lipid class. Along with carbohydrates and proteins, fats and oils are one of the main components of the cells of animals, plants, and microorganisms. Fats and oils have the general formula
where R’, R”, and R’” are fatty acid radicals. All known natural fats and oils contain three different acid radicals that are unbranched and usually contain an even number of carbon atoms. The saturated fatty acids most often found in fat and oil molecules are stearic and palmitic acids, and the main unsaturated fatty acids are oleic, linoleic, and linolenic acids. The physicochemical and chemical properties of a fat or oil are determined to a considerable degree by the ratio of its component saturated and unsaturated acids.
Fats and oils are insoluble in water and readily soluble in organic solvents; they are usually slightly soluble in alcohol. When treated with superheated steam, inorganic acids, or alkali, fats undergo hydrolysis (saponification), with the formation of glycerol and fatty acids or their salts. Emulsions are formed by vigorous agitation with water. An example of a stable aqueous fat emulsion is milk. The emulsification of fats in the intestines (a necessary condition for their absorption) is effected by salts of bile acids.
Natural fats are subdivided into animal and vegetable fats. Fats are the main source of energy in the body. The energy value of fats is more than twice as great as that of carbohydrates. The fats that are components of membrane formations of the cell and subcell organelles have important structural functions. Because of its extremely low heat conductivity, the fat deposited in the subcutaneous fatty cellular tissue acts as a heat insulator, protecting the body from heat loss, which is particularly important in the case of warm-blooded marine animals, such as whales and seals. In addition, fat deposits provide the pronounced elasticity of skin. The fat content of the human body and the bodies of animals varies greatly. In cases of great corpulence and of hibernating animals before hibernation, the fat content of the body reaches 50 percent. When farm animals are fattened, their fat content is particularly high. In the body a distinction is made between reserve fats, which are deposited in the subcutaneous fatty cellular tissue and in the omentum, and protoplasmic fat, which is a component of protoplasm in the form of complexes with proteins, called lipoproteins. In case of starvation or inadequate feeding, the reserve fat disappears, but the percentage of protoplasmic fat in the tissues stays almost the same, even when the body is extremely emaciated. Organic solvents readily extract reserve fat from fatty tissue. Protoplasmic fats can be extracted from fatty tissue with organic solvents only if the tissues have been previously treated to denature the proteins and split up their complexes with fats.
Plants contain relatively small quantities of fats. Exceptions are oil-producing plants, whose seeds differ in that they have a high oil content.
REFERENCES
Karrer, P. Kurs organicheskoi khimii, 2nd ed. Leningrad, 1962. (Translated from German.)Ferdman, D. L. Biokhimiia, 3rd ed. Moscow, 1966.
Tiutiunnikov, B. N. Khimiia zhirov. Moscow, 1966.
Kretovich, V. L. Osnovy biokhimii rastenii, 5th ed. Moscow, 1971.
IU. N. LEIKIN