fats and oils
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fats and oils,group of organic substances that form an important part of the diet and also are useful in many industries. The fats are usually solid, the oils generally liquid at ordinary room temperatures. Some tropical products, liquids in their sites of origin, become solids in cooler climates; in commerce these often retain the name originally given, e.g., palm oil and coconut oil. Chemically fats and oils are either simple or mixed glyceryl estersester,
any one of a group of organic compounds with general formula RCO2R′ (where R and R′ are alkyl groups or aryl groups) that are formed by the reaction between an alcohol and an acid.
..... Click the link for more information. of organic acids belonging to the fatty-acid series (see triglyceridestriglyceride,
ester formed from glycerol and one to three fatty acids. Fats and oils are triglycerides. In a simple triglyceride such as palmitin or stearin, all three fatty-acid groups are identical.
..... Click the link for more information. ; fatty acidsfatty acid,
any of the organic carboxylic acids present in fats and oils as esters of glycerol. Molecular weights of fatty acids vary over a wide range. The carbon skeleton of any fatty acid is unbranched. Some fatty acids are saturated, i.e.
..... Click the link for more information. ). Fats and oils are derived from both plant and animal sources.
Commercial Processing of Fats
Among the vegetable oils of greatest commercial importance are cottonseed, linseed, olive, palm, corn, peanut, soybean, and castor oils. The method of obtaining the oils is similar for all: the fruits or seeds after being cleaned are crushed and pressed cold to obtain the highest grade of oil and then pressed warm, yielding a grade suitable for industrial use. Sometimes solvents are used to remove the remaining oil from the crushed mass. Edible oils are those used in foods, and for these the highest grade is utilized; these must be pale in color, free from disagreeable odor and taste, and wholesome. The lower grades are suitable for making soap and for other industrial purposes. The chemical property that makes fats solid and oils liquid is the amount of saturation in the ester (see saturated fatssaturated fat,
any solid fat that is an ester of glycerol and a saturated fatty acid. The molecules of a saturated fat have only single bonds between carbon atoms; if double bonds are present in the fatty acid portion of the molecule, the fat is said to be unsaturated.
..... Click the link for more information. ). Animal fats are esters of saturated fatty acids; vegetable oils are esters of unsaturated fatty acids.
Conversion of liquid vegetable oils into solid fats is an important chemical industry. This process, sometimes called hardening, involves hydrogenation of the unsaturated fatty-acid portion of the oil molecule by heating the oil with hydrogen in the presence of a metal catalyst; by controlling the extent of hydrogenation, various products can be obtained. For example, controlled hydrogenation of cottonseed oil produces a solid vegetable cooking fat. Most fats become rancid upon standing; since a major factor leading to rancidity is air oxidation of double bonds (to form foul-smelling aldehydesaldehyde
[alcohol + New Lat. dehydrogenatus=dehydrogenated], any of a class of organic compounds that contain the carbonyl group, , and in which the carbonyl group is bonded to at least one hydrogen; the general formula for an aldehyde is RCHO, where R is hydrogen
..... Click the link for more information. ), saturated fats are much more resistant to rancidity than unsaturated fats.
Fats as Food
Animal fats used in foods include butter, lard, chicken fat, and suet. Cod-liver oil and some other fish oils are used therapeutically as sources of vitamins A and D. Nutritionally fats and oils are valued as a source of energy. Because they contain less oxygen than other nutrients, they oxidize more readily and release more energy. Fats are digested in the human body chiefly by the enzyme lipase (in the pancreatic juice) aided by the bile. There are several theories to explain the method of absorption of fats; favored by many is the view that they are absorbed by the epithelial cells of the lining of the small intestine in the form of the fatty acids and glycerol into which they are split by digestion and that a recombination to re-form the fat occurs within the cells. Most of the fat then enters the lymphatic system through the villi in the lining of the small intestine, although some is probably absorbed directly by the blood vessels of the villi. Medical research indicates the possibility that saturated fats in the diet contribute to the incidence of arteriosclerosisarteriosclerosis
, general term for a condition characterized by thickening, hardening, and loss of elasticity of the walls of the blood vessels. These changes are frequently accompanied by accumulations inside the vessel walls of lipids, e.g.
..... Click the link for more information. ; such fats may raise the blood's level of cholesterol, which is deposited in the arteries.
term commonly used to indicate a variety of greasy, fluid substances that are, in general, viscous liquids at ordinary temperatures, less dense than water, insoluble in water but soluble in alcohol and ether, and flammable.
..... Click the link for more information. ; petroleumpetroleum,
oily, flammable liquid that occurs naturally in deposits, usually beneath the surface of the earth; it is also called crude oil. It consists principally of a mixture of hydrocarbons, with traces of various nitrogenous and sulfurous compounds.
..... Click the link for more information. .
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.
REFERENCESKarrer, 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