World Fat and Oil Production

Current production estimates for important fats and oils are shown in Figure II. E.1.2. Soybean oil is by far the leader, followed by palm, sunflower, and rapeseed oil, with others trailing far behind. The current levels of production of the various vegetable oils reflect relatively recent changes. Palm oil production has increased dramatically in the last few decades, as Malaysia and other Asian countries have promoted it, and in the past half century, soybean oil, once a minor oil, has become the most widely used of all.

Today, fat and oil usage differs markedly between developed and developing countries, with the per capita consumption of fats and oils in industrialized nations about 26 kilo grams (kg), compared to a world average of 7 kg.

Historically, northern Europeans developed diets based on animal fats because their climate was unsuited for growing oilseed crops and their pastures allowed animals to be raised with relative ease. In areas of Scandinavia, where fishing was a major means of food production, the diet contained large amounts of marine fats.

In Africa, Asia, and the Mediterranean, however, because the raising of large numbers of animals was impractical and fish were not dietary mainstays, fats were derived primarily from plants, such as oil palms and olive trees. Thus, historical differences in patterns of fat consumption largely resulted from environmental conditions that fostered the various agricultural practices of the different areas of the world.

Yet, over the past 100 years, there has been a decreased consumption of animal fats and an increase in that of vegetable oils. When vegetable oils were first produced in commercially important quantities, they could not be used to displace animal fats because the latter (for example, butter, lard, and tallow) were solid at room temperature and had specific applications that required solidity. But the process of hydrogenation, developed early in the twentieth century, permitted the manufacture of plastic fats (such as shortening and margarine) based on vegetable oils, and lard and butter were subsequently displaced in the diets of many peoples.

The twentieth-century industrialization of oilseed production, as well as vegetable oil extraction and refining, has been the primary factor leading to large-scale changes in the fat composition of diets around the world, although genetic engineering, breeding, and mutation have also brought significant changes in the fatty acid composition of a number of oilseeds. Moreover, the fatty acid composition of animal fats and aquacultured fish can be altered by dietary manipulation. Such changes complicate discussion of the nutritional benefits obtained from oils.

Oil Extraction and Processing

A knowledge of the ways in which oils are obtained (extracted) and processed is important to an understanding of the nutritional value of the oils. Fats and oils are extracted from animal and vegetable materials by the three main processes of rendering, using the screw press, and solvent extraction.

The first method humans employed to extract oils was undoubtedly rendering, which is still used today to remove fat from animal and fish tissues. In this process, the material to be rendered is heated (either dry or in water), which disrupts the tissues and allows separation of the oil. The quality of the oil yielded by early rendering operations must have been poor, but later developments in processing (such as steam heating) have permitted the rendering of high-quality products. The conventional wet-rendering process includes an initial cooking step, in which the tissue is heated with direct or indirect steam, or is heated as it passes through a conveyer. The cooked material is pressed in continuous or batch presses, and the liquid (“press liquor”) is centrifuged to separate the water and oil. The oil obtained may be dried further before storage.

Figure II. E.1.2. Production estimates for important fats and oils.

Table II. E.1.1. Average oil content of plant sources of oil

In the second method, an expeUer, or screw press, removes oil from vegetable materials by mechanical pressure. The pressure creates heat, disrupting the tissue and causing the oil to separate, after which it flows out through holes in the press. Such presses have been documented in early Hindu medical texts; the first of these devices, however, doubtless had low output, and the extracted oil was probably used for illumination or for medicine. These were batch presses, which had to be filled with oilseed and then emptied in each extraction step. By contrast, modern screw presses operate continuously and have much greater capabilities than batch presses. Screw-press extraction of oil is most feasible when the oil content of the material to be pressed is high. The oil content of some vegetable sources of oil is shown in Table II. E.1.1 (Sonntag 1979a).

The third method of oil recovery, solvent extraction, was only possible after supplies of solvents with appropriate characteristics became available. The solvent-extraction process for soybeans is outlined in Figure II. E.1.3.The refining steps include alkali neutralization, which results in the removal of phospholipids and free fatty acids; bleaching, which removes pigments, metals, and free fatty acids; and deodoriza-tion, which removes odorous compounds, some sterols, and tocopherols.

W Normann’s discovery of liquid phase hydrogenation (which results in loss of polyunsaturated fatty acids and production of monounsaturated “trans” acids) led to the development of plastic fats derived from vegetable sources. Crisco, the first shortening to be sold (1911), was based on hydrogenated cottonseed oil. By the mid-1940s, 65 percent of the cottonseed oil produced in the United States was used to make shortening.