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By volume, soybean oil represents the most important single product in the vegetable oil production of both the United States and the world. The oil is produced from mature, shelled soybeans, either by solvent extraction or by pressure expellers. The latter process has been largely replaced by extraction with a light petroleum solvent such as hexane, a method by which over 95 per cent of the United States product is derived. The yield of oil is about 16 to 18 per cent of the bean, or about 10 to 11 pounds per bushel. The crude oil thus obtained contains some 2 to 4 per cent of phosphatides or "lecithin," which may be separated by heat treatment followed by centrifuging. When the oil is destined to be used for edible purposes, it is usually refined by treatment with dilute caustic alkali, which removes the traces of free fatty acids and other impuritjes. It is then decolorized by treatment with activated bleaching clays, and deodorization is accomplished by treatment with steam under vacuum conditions.
The principal use of this oil is for food purposes, such as the manufacture of shortenings and margarine. Substantially all of the oil used for shortenings and margarine is hydrogenated. This process involves treatment of the oil, at elevated temperatures, with hydrogen gas under pressure and in the presence of a special nickel catalyst. The hydrogen reacts with the unsaturated fat molecules to produce the corresponding saturated fats, which have a higher melting point and improved consistency. Considerable quantities of soybean oil are used for other edible purposes, such as salad and cooking oils, for which use the oil is not hydrogenated but is often blended with olive oils.
For nonfood purposes, soybean oil is widely employed in the drying oil industry, that is, in such products as paints, varnishes, linoleum, and printing ink. Another major industrial use is in the manufacture of alkyd resins, where the oil is reacted chemically with phthalic anhydride and glyc-erol to form a synthetic resin which, in turn, is extensively used in the manufacture of paints and varnishes. Distilled grades of soybean oil fatty acids are commonly produced from the so-called "foots," which are residues resulting from the alkali refining of the crude soybean oil for edible purposes.
This oil is manufactured from the delinted, decorticated cottonseed. The clean seed meats are first passed through a series of pressure rolls to produce thin flakes, after which the flakes are cooked under steam pressure, which ruptures the oil cells. Subsequently, the flakes are either pressed in hydraulic presses or processed in continuous screw-type expellers which remove the oil under high pressure. The solvent extraction method is gaining acceptance, although not to as great an extent as in soybean oil production. Average yield of oil is about 16 to 17 per cent of the cottonseed. Treatment of the crude oil to produce refined grades is similar to that used for soybean oil; it involves alkali refining to remove color bodies and other nonglyceride impurities, bleaching with activated clays, and, finally, steaming under vacuum conditions to remove traces of odor.
The principal end uses of cottonseed oil are similar to those of soybean oil, namely the production of shortenings and margarine. For both of these products, the oil is hardened by hydro-genation, which increases the melting point, improves the stability of the oil against oxidation, and also improves the plasticity to produce a desirable solid product.
Miscellaneous uses of cottonseed oil include the manufacture of biscuits, crackers, doughnuts, confections, and potato chips, and the preparation of ice cream substitutes (mellorines), in which process the oil replaces butterfat. Industrial uses include alkyd resins for interior paints, special lubricants, and soft soaps.
Flaxseed is the source raw material for linseed oil. It is grown principally in Canada, Argentina, and the United States, with smaller amounts produced in India. United States output was increasing in the late 1950's, the principal areas of production being in North and South Dakota and Minnesota. Argentina and Canada are the largest exporters, followed by the United States and India. ,
Two methods of production are used, these being solvent extraction and continuous screw-press expelling. The seeds are not usually decorticated before pressing. The yield of oil is 35 to 37 per cent, or about 19 to 20 pounds per bushel of seed.
Since linseed oil is in the drying oil category, it is most extensively employed in protective and decorative coatings, such as paints and varnishes, which accounts for the major share of world production. Substantial amounts are used also in the manufacture of linoleum and oilcloth and alkyd resins.
In world vegetable oil production, peanut oil ranks second only to soybean oil. It is produced by screw-press expeller and solvent extraction methods. The oil content of the peanut kernels varies between 45 and 55 per cent. Major producing countries are India, China, French West Africa, Nigeria, and the United States.
Peanut oil is an excellent edible oil and the major part of the world production is destined for consumption as food. For edible purposes, it may be hydrogenated or used as is, as in mayonnaise or salad oil. In general, its uses are much the same as those of cottonseed and soybean oil.
Coconut oil is the major oil crop produced by a species of the broad family of palm trees. It is expressed from the dried meat of the coconut. The importance of this meat, known in commerce as copra, may be illustrated by the fact that coconut oil constitutes, on an average, about 8 per cent of the world's supplies of all fats and oils. The principal copra-producing countries are the Philippine Republic, Ceylon, India, Indonesia, and Malaya. Most of the world production of coconut oil and/or copra is exported, the Philippine Republic producing more than half of the total weight of oil and copra (calculated as oil) in the world export trade. (Prior to World War II, the United States absorbed over 80 per cent of the Philippine export, but by 1959 a substantial trade had been developed with European countries, particularly the Netherlands, mostly in the form of copra.)
Copra is processed for its oil content, the principal methods being hydraulic pressing and pressure expelling in continuous screw presses. The yield of oil from copra averages 63 per cent. The resulting crude oil may then be refined, bleached, and deodorized for edible uses. For other uses, such as soap manufacture, the oil is customarily alkali-refined and bleached with activated clays in the same manner as other fats and oils.
The major end use of coconut oil is in food products. During World War II, all shipments from the Far East were cut off, resulting in a marked decline in coconut oil usage throughout the world. Other oils were substituted and after the war the trend to lower consumption has been steady, due largely to the higher price structure of coconut oil in relation to competing oils. In its food uses, coconut oil is principally employed in the production of margarine, biscuits, crackers, and candy.
The principal industrial use of coconut oil is in soap products, particularly in toilet soaps, the fat content of which averages about 18 per cent coconut oil, the balance being inedible tallows and greases. The inroads of synthetic detergents into the soap market, since World War II, are reflected in the declining use of coconut oil for soapmak-ing. Currently, however, some of the brands of synthetic detergents also use coconut oil as raw material, offsetting, to some extent, the decline in its use in soap manufacture. The unique fatty acid composition of the oil, which is high in lauric and myristic acids, has been responsible for the development of other industrial uses. These involve converting the oil into chemical derivatives, such as fatty alcohols, amines, and amides of the mixed or separated acids.
Derived from the seed of a plant in the Brassica family, rapeseed oil is produced and used chiefly in the countries of origin, China, India, Pakistan, and Japan, and to a lesser extent in some European countries. The seed contains about 40 per cent oil content, which is extracted by the conventional methods used for other oils, namely, pressure expelling (by either continuous or hydraulic pressure) and solvent extraction. Rapeseed oil is used chiefly for food. Industrial uses include lubrication and soap manufacture, and in some countries of origin the oil may also be burned in lamps.
World olive oil production is very substantial, most of the supply being produced and consumed in the countries adjacent to the Mediterranean basin, including Spain, Italy, Greece, Portugal, and Turkey. Cold pressing of the ripe fruit is followed by one or more hot pressings. The residue or cake resulting from these pressings may be extracted for additional oil by means of solvents. The yield of oil varies between 15 and 40 per cent.
Olive oil is chiefly employed as food in the countries of origin. In contrast to other oils, it is customarily used in its original form, that is, unhydrogenated. Industrial uses for the lower grades include the production of soaps, textile lubricants, sulfonated oils, cosmetics, and pharmaceuticals.
Palm oil is derived from the outer, fleshy fruit of the palm trees indigenous to many Asiatic and African countries. The oils are usually designated as native or plantation and may be further identified by country of origin, such as Malaya, Sumatra, Congo, Lagos, or Nigeria.
The kernel of the palm fruit produces palm kernel oil, which has a quite different composition from the fruit oil, resembling much more closely the coconut oil derived from copra. The kernels are produced mainly in Africa, whence they are shipped to Europe for extraction of the oil content.
The oil derived from the fruit of the palm has a deep orange-red color and has the composition and general characteristics of animal fats. The palm fruit grows in large clusters, and, due to the high moisture content, is particularly susceptible to deterioration, which in turn depreciates the quality of the oil. Hence, the fruit is usually sterilized by steaming, after which the oil is rendered by heating in either open kettles or closed digestors. The oil is then separated from the fruit pulp by hydraulic presses or basket-type centrifuges. The extracted oil may be further refined by heating with steam, water washing, and final centrifuging.
The principal use of palm oil is for food purposes in European countries, where it is refined and further processed into shortening and margarine-type products. In the United States it has a special use in the production of tin plate, where it acts to lubricate and protect the tin film, which is applied in molten form to the base steel sheet.
While the volume of world production is not relatively large, corn oil is an important article of commerce. It is derived from the corn germ, the yield of oil being about 45 per cent of the germ. Production methods usually employed are similar to those for cottonseed. The resulting oil is a dark, amber liquid whose color cannot be entirely removed by refining and bleaching. Corn oil is usually processed for salad (mayonnaise) or cooking oils. This is partly because of the preferred amber color, but more so because the oil does not require winterization. For salad purposes, oils such as cottonseed must be winterized, which involves chilling the oil and filtering out the fats which have high melting points.
Production of castor oil is not great in volume, but it remains an important commodity. Most of the castor bean crop originates in Brazil and India, which together account for about 60 to 65 per cent of the world output. China (including Manchuria) and Thailand are the next largest producers.
Castor oil is produced by solvent extraction of the beans, usually in batch operation, as contrasted to the usual continuous-extraction methods used with soybeans. The yield of oil is high, being about 42 to 45 per cent of the whole bean.
The largest single use for castor oil is in protective coatings, such as paints, lacquers, and varnishes. For this use it is chemically modified by dehydration of the major constituent, namely ric-inoleic acid, which process gives the oil quick-drying properties. Castor oil is also used in all-purpose greases, hydraulic fluids, Pharmaceuticals, printing ink, and plasticizers.
Tung oil, sometimes called Chinawood oil, is produced by pressing or expelling the fruit of the tung tree. In the past, China was the principal source of the oil, where it was expressed by very primitive methods from the fruit of wild tung trees. The variable and often poor quality of the oil thus produced led to the cultivation of the trees in other parts of the world, such as the United States, Argentina, and Brazil, although China is still the largest producer. The yield of oil from the nuts is about 16 to 17 per cent.
Because of its relatively high iodine number and unusual fatty acid composition, tung oil is chiefly used as a drying oil in protective coatings. In conjunction with phenol resins, it makes an excellent spar varnish, noted for high water resistance.
Miscellaneous Vegetable Oils
Among the less common vegetable oils of which substantial amounts are produced in the world, the following deserve mention: sunflower, sesame, perilla, and oiticica, all of which are in the semidrying or drying categories. In the nondrying group and similar in many of their properties to coconut oil are several oils of the palm species, including palm kernel oil, and babassu, murumuru, and cohune oils.