Vegetable Oils Olive Oil

Olive oil is derived from the fruit of the evergreen tree Olea europaea, which grows in temperate climates with warm and dry summers. Around 5,000 or 6,000 years ago, at the eastern end of the Mediterranean, the tough, spiny, wild olive trees dominating the countrysides of Palestine, Syria, and other areas of

Figure II. E.1.3. Operations in soybean oil extraction and refining.

The Middle East were first brought under cultivation (Chandler 1950). The trees became gnarled with domestication, and less bushy, and their fruit (green that ripens to brown or to blue-purple-black) was laden with oil. That oil - technically a fruit oil rather than a vegetable oil, as it is classified - doubtless was used to fuel lamps, and it found its way into medicines and cosmetics as well as cooking. The many uses for oil created much demand in the ancient world, which was satisfied by oils made from walnuts, almonds, and the seeds of sesame, flax, and radishes, as well as from olives (Tannahill 1988). The latter, however, were the most productive source of oil from the Bronze Age onward, and their cultivation spread throughout the Mediterranean region, so that the waning centuries of that age found the people of the island of Crete cultivating great numbers of olive trees and growing rich on the export of oil (Trager 1995).

Shortly after the dawn of the Iron Age, the Greek landscape reflected a similar dedication to olive production, spurred in the early sixth century B. C. by the prohibition of Solon (the Greek statesman and legal reformer) of the export of any agricultural produce except olive oil. Greece (like Crete, two millennia earlier) would learn how devastating the effects of monoculture could be when war made trade impossible (Tannahill 1988).

Nevertheless, as a relatively precious product requiring special climate and skills, yet easy to store and ship in jars, olive oil lent itself well to this kind of specialization. Barbarians in contact with the Greeks became good customers, although any possibility of

Greek monopoly ended when Etruscans carried the techniques of olive cultivation into Italy, and Phoenicians did the same for North Africa and the Iberian peninsula.

Because many years are required for olive trees to become productive after planting, olive cultivation in these new areas probably required the passing of a generation or two before its possibilities were appreciated. But certainly one thing worth appreciating was that olive trees seemed to live forever. In Spain, for example, it is said that there are trees some 1,000 years old, which meant that in the absence of some catastrophe, such as disease or fire, the task of planting olive trees and then waiting for them to become productive seldom troubled grove owners more than once, if that (Chandler 1950).

In the first century A. D., Pliny noted a dozen varieties of olives grown as far away from Rome as Gaul (France) and Spain, and certainly it was the case that by the time of the Romans, olive-tree cultivation had caught on in Iberia in a big way. With olive oil a staple in the Roman diet, Spanish oil was a commodity sought throughout the Empire, and henceforth olive oil would be established as the most important dietary oil in southern Europe. In the north - where livestock did well and olive trees did not - cooking was done with butter and lard. Obviously, the cuisines these cooking mediums helped to shape were often strikingly dissimilar.

Within fourteenth-century Spain, olive oil was exported from south to north, and wool and hides from north to south, in a kind of microcosm of greater Europe, and, following the conquest of the New World, American demand continued to stimulate Spain’s olive oil industry. As the colonists began to make their own oil, however, the flow of Spanish olive oil across the Atlantic diminished. In North. America, Thomas Jefferson tried to grow olives at Monticello, but the cuttings he used would not take root (Trager 1995). At about the same time as this failed experiment in the east of the continent, olive cultivation was successfully launched in California by Spanish missionaries, and by the beginning of the twentieth century, that western state had joined Provence in France and the Lucca district in Italy - in the eyes of at least one American writer - as a producer of some of the world’s best olive oils (Ward 1911).

Today, 90 percent of the world’s olives go into oil, and only 2 percent of the acreage given over to olive production is outside of the Mediterran-ean region (McGee 1984). In terms of volume, Spain, Italy, Greece, and Portugal are the largest producers, although much of their olive oil is not reflected in production figures because there are many people - with just a few trees - who pick their own olives and take them to local cooperatives to be pressed.

Olives are sometimes picked by hand because they, and the twigs they grow upon, are fragile. However, because the fruit should be all of the same size and degree of ripeness, the same tree might be picked several times, all of which significantly increases the price of the oil (Toussaint-Samat 1992). To avoid picking several times, the fruits are generally treated less elegantly and are knocked off the trees, either from ground level with long poles or with small rakes by harvesters who climb the trees to shower the olives down. The fruits are caught on cloths spread on the ground or (more frequently today) on sheets of plastic.

Olives to be eaten are usually picked green and unripe. But, as Harold McGee (1984: 204) has remarked, anyone who has ever bitten into one knows instantly that something more must be done to render it edible. This something more is generally pickling, which has been practiced since the days of ancient Rome by soaking olives in a solution of lye to remove the bitter glucoside called oleuropein (from Olea europea).

Black olives - those that ripen at the time of the first frosts - are the kind made into oil. After they are gathered, they are permitted to stand and get warm, but not to ferment. Then they are washed and crushed. The oldest known technique for extracting oil was that of crushing the fruit underfoot; later, crushing was done by hand, using a pestle, and later still with millstones. In fact, many of the old-style Roman oil mills, with their large millstones operated by donkeys or mules (or by slaves in Roman times) continued in use throughout the Mediterranean area until well into the twentieth century (Toussaint-Samat 1992).

The crushing results in a paste that is pressed to secure the 25 to 30 percent of the olive that is oil. Extra virgin oil, also called “cold-pressed,” comes from the first and lightest pressing and is unrefined; moreover, no heat is used to extract further oil. Virgin oil is produced in the same manner but has slightly greater acidity. Cold-pressed olive oil, although it has a wonderful flavor, will not keep as well as refined olive oil and, consequently, must be shielded from the light in cans or dark bottles.

The oil produced by succeeding pressings (usually with heat or hot water added) generally contains substances that give it a bad flavor, whereupon it is refined. Light and extra light oils are olive oils (not virgin) that have been filtered, producing a light scent, color, and taste. Oil labeled “pure” is a combination of virgin oil and that derived from the second pressing. Production of olive pomace oil - the cheapest grade of olive oil - requires hot water, which is added to the residue of olive oil cake, then poured off. This oil, typically not very good, has traditionally been exported to countries where a taste for olive oil has not been highly developed, although it is sometimes consumed by its own producers, who in turn sell their virgin oils for income (Toussaint-Samat 1992).

A more complicated (and technical) grading system for olive oils is based primarily on the free fatty acid levels: Extra virgin oil, which comes from the first pressing, has an acidity of less than 1 percent and perfect flavor and odor. Virgin oil, from the same pressing, contains less than 3 percent free fatty acids. Extra virgin and virgin olive oils may be processed only by washing, decantation centrifugation, and filtration. Refined olive oils are obtained by refining virgin or extra virgin olive oils, using the same alkali neutralization, bleaching, and deodorization steps employed in refining other oilseeds. Olive pomace oil is produced by solvent extraction from the cake remaining after pressing. It was sometimes called sulfur olive oil in the past, when carbon disulfide was used as an extraction solvent.

To maintain low free fatty acid levels and produce oil of the highest quality, olives must be processed within three days of harvest. This is primarily because ripe olives contain a high amount of water, allowing lipase enzyme activity and a resulting increase in free fatty acid levels. Consequently, in some areas that are not equipped to press olives as fast as they are harvested, either the fruit is left on the trees until it can be processed, or it is stored, which can be a risky procedure.

Olive oil is characterized by a very high oleic acid content averaging around 75 percent (Table II. E.1.2). Palmitic acid is the second most prevalent fatty acid, followed by linoleic and linolenic. There has been a great deal of interest in olive oil as a promoter of human health since the development of the hypothesis that a “Mediterranean diet” is protective against heart disease, perhaps because for centuries, olive oil has been the only oil readily obtainable for human use that has a high oleic characteristic.

Recent developments in oilseed breeding and genetics, however, have produced high-oleic safflower, sunflower, peanut, canola, and soybean oils. Yet, it is unlikely that these will take over the applications of olive oil, which is enjoyed as much for its flavor as for any nutritional advantages it may have. As already noted, because they are not refined, virgin olive oils have a pleasant and characteristic flavor, and of all the major vegetable oils, only olive oil is sold unrefined. The deodorization process undergone by other oils removes compounds that would otherwise produce flavors unsuitable for many applications. In addition, some oils have flavors that can only be characterized as unpleasant.

Olive oil has a moderate amount of tocopherols, primarily alpha-tocopherol. Despite a low level of gamma-tocopherol, olive oil is remarkably stable, which is attributable to its low levels of linoleic and linolenic acids, as well as phenolic compounds that are present. Minor components in olive oil are not removed because the oil is not refined; the levels of some of these compounds are shown in Table II. E.1.3. Finally, it should be noted that olive oil contains very low levels of phospholipids and waxes, which permits the production of a clear oil without refining.

Table II. E.1.3. Levels of minor components in olive oil

Soybean Oil

The soybean (Glycine max L., formerly Soja max), of the family Leguminosae, is grown worldwide for its high-protein content and its oil. There are wild (Glycine ussuriensis) and intermediate (Glycine gracilis) as well as cultivated (G. max) soybean varieties. Although soybeans have been used as food in China for thousands of years, their development as the world’s primary oilseed has only taken place since the mid-1940s.

As mentioned (and as shown in Figure II. E.1.2), the production of soybean oil today overshadows all others. The soybean contains 40 to 50 percent protein and an average of 18 to 20 percent lipids (Table II. E.1.1). Its oil is a byproduct of the production of soybean meal, which is primarily used as animal feed. The oil obtained directly from soybeans contains about 88 percent neutral lipid (triacylglycerols and sterols), 10 percent phospholipid, and 2 percent gly-colipid. Refined oil contains more than 99 percent tri-acylglycerols, and it is necessary to remove the phospholipids to produce a stable, clear oil. Like other vegetable oils, save that from olives, soybean oil is usually refined, bleached, and deodorized before use.

Soybeans contain a number of antinutritional compounds, including protease inhibitors, hemagglutinins, saponins, goitrogens, allergens, phytic acid, and oligosaccharides (raffinose, stachyose), as well as isoflavones (phytoesterogens). However, because these compounds are not transferred to the lipid, the oil is essentially devoid of them.

Soybean oil is one of the two common oils that contain appreciable levels of omega-3 fatty acids, and it is ironic that at the same time that some investigators were discovering the important roles played by omega-3 fatty acids in the human diet, other researchers were working to reduce the levels of these fatty acids in soybean oil (Hammond 1992).The reason for the interest in lowering linolenic acid in soybean oil (which ranges from 55 to 10 percent) is that it oxidizes at a rate some 2 or more times greater than linoleic acid, which, in turn, oxidizes at a rate about 10 times lower than oleic acid (Hammond 1994). Lowering linolenic acid levels results in a more stable oil; the more unsaturated the oil, the less stable it will be. In the past, soybean oils have been lightly hydrogenated (brush hydrogenation) to reduce the linolenic acid content to less than 3 percent. This is uncommon today because of health interests in oils with no trans acids and also because of problems with cloudiness at refrigeration temperatures.

Recently, there has also been a great deal of interest in reducing the amount of palmitic acid in soybean oil, which is a major dietary source of it. This is because palmitic acid is thought to be one of the three saturated fatty acids most responsible for raising plasma cholesterol in humans (the other two are myristic acid and lauric acid). Varieties of soybeans with modified fatty acid composition have been developed, including low-linolenic, high-stearic, high-oleic, high-palmitic/low-linolenic, high-palmitic, and low-saturate/low-linolenic.

The low-saturate/low-linolenate composition, shown in Table II. E.1.4, has much lower palmitic acid levels than traditional soybean varieties; the other fatty acids are relatively constant. The linolenic and oleic acids are at the high end of the fatty acid ranges in normal soybeans. Lowering the palmitic acid content of soybeans has been a major improvement in terms of nutritional value, and more varieties of oilseeds with tailor-made fatty acid compositions for specific purposes should be seen in the future.

The tocopherol composition of soybean oil is shown in Table II. E.1.5. It should be noted that, in some reported analyses of vitamin E compounds, the beta and gamma isomers are combined, whereas other analyses do not report these isomers. The beta and gamma tocopherols are very similar in structure (Figure II. E.1.4). For most vegetable oils, the alpha and gamma isomers predominate. The alpha isomer is by far the most bioactive of the tocopherol isomers (Table II. E.1.6), but the antioxidant effect appears to be greater for the gamma isomer. Tocopherols are reduced during the refining process at the deodoriza-tion stage. Roughly 30 percent of the total tocopherols are removed. The data presented in Table II. E.1.6 are for refined, bleached, and deodorized (RBD) oils.

Table II. E.1.4. Fatty acid compositions (weight percentage) of modified fatty acid vegetable oils

Table II. E.1.5. Tocopherol isomer distribution in dietary fats and oils (pg/g)

Table II. E.1.6. Approximate biological activity relationships of vitamin E compounds

Compound

Percentage activity of d-a-tocopherol

Figure II. E.1.4. Tocopherol composition of soybean oil.

Palm Oil

Although there are many different palms that can provide oil, palm oil of commercial importance is obtained from the African oil palm, Elaeis guineensis. The name Elaeis is derived from the Greek word for oil. Palm oil is obtained from the fruit, whereas palm kernel oil comes from the seed kernel. Their fatty acid compositions are different, with palm kernel oil having a high content of lauric acid (palm kernel oil is similar to coconut oil in fatty acid composition). Palm oil is currently one of the most common oils worldwide, and oil amounts have increased dramatically since the 1980s.

Palm oil use in human diets can be dated back as far as 3000 B. C. Crude palm oil has a long history of use in western Africa, and in the eighteenth century, trade in the oil began between Africa and Europe. Wild palms are still a significant source of oil in West Africa, but recent increases in oil-palm cultivation have occurred in Latin America and Southeast Asia, with about 70 percent of present-day world palm oil production centered in the latter region.

Palm is the highest yielding of the oil-bearing plants, with an average of between 4 and 10 tons of oil per hectare per annum. Three types of palm have been characterized: Dura, with a thin flesh and thick, hard shell;pisifera, with thick flesh and little or no shell; and tenera, with a thick flesh and intermediate shell. The tenera variety is a cross between a dura female and pollen-bearing pisifera. Because the progeny of tenera are not uniform, cloning (asexual reproduction) of this palm has been practiced to improve yield and quality.

Traditional processing of palm to obtain palm oil, as practiced by the local populations, includes separation of the fruit, softening of the fruit, maceration, pressing, and oil purification. The softening process usually takes place by allowing the fruit to ferment in a pile for several days. The fruit may be further softened by boiling and then maceration in a mortar. After placement in a large oil-impermeable container, the oil is separated by kneading the material. Oil is skimmed from the top and may be filtered and then heated to remove the water.

The quantity of recovered oil in older traditional processing was low (less than 40 to 50 percent of total oil), and the quality of this crude oil was poor, compared to oil extracted and refined with more modern methods. If the fruits are not quickly heat treated, the free fatty acid level increases rapidly because of fungal lipases, and indeed, free fatty acid contents as high as 50 percent have been measured in traditionally processed oils. The flavor of oil with a high free fatty acid content is preferred in some areas of West Africa, where palm oils have traditionally been unrefined and have always had a high free fatty acid content. However, for most people, very high free fatty acid levels usually make the oil unsuitable for food use and more amenable to industrial applications, such as soap making. Oils obtained from wild trees by traditional processes are classified as soft (less than 12 percent),

Table II. E.1.7. Nontriacylglycerol materials in crude palm oil

Semisoft (less than 35 percent), or hard (greater than 45 percent), depending on the free fatty acid levels.

Crude palm oil contains a number of nontriacyl-glycerol components, including carotenoids, toco-pherols and tocotrienols, sterols and sterol esters, phospholipids, and hydrocarbons (including squalane). The levels of these compounds in crude palm oil are shown in Table II. E.1.7. Palm oil contains very high levels of tocopherols and alpha tocotrienal (Table II. E.1.5).The carotenoids include lycopene and alpha and beta-carotene and are the cause of the deep red color of the oil. The main carotenoids are alpha-and beta-carotene, which make up over 90 percent of the total. Although there is experimental evidence linking dietary intake of carotene with protection against some types of cancer, the current practice is to remove the carotenes by bleaching to produce light-colored oil. Moreover, removing the carotenoids substantially improves the oxidative stability.

Recently, there has been a campaign virtually condemning the so-called tropical oils (palm, palm kernel, and coconut oils) as bad for human health. The argument has been that because they are high in saturated fats, these oils raise cholesterol levels in the body. Food products have been labeled “we use no tropical oils,” their manufacturers and processors employing partially hydrogenated oils instead. Yet the notion that the addition of tropical oils to food products could lead to an increase in cardiovascular deaths ignores the fact that at least in Western diets (and especially in the United States), animal products and soybean oil are the main sources of saturated fats in the diet. It also ignores the cloud of suspicion now enveloping the use of partially hydrogenated oils.

The fatty acid composition of palm oil is quite different from that of coconut or palm kernel oil. The latter are lauric oils with about 80 to 90 percent saturated fat, predominantly lauric acid (41 to 55 percent), myristic acid (13 to 23 percent), and palmitic acid (4 to 12 percent). Palm oil is rich in oleic acid and low in saturates (less than 50 percent), relative to coconut and palm kernel oils. Experimental evidence so far indicates that there is no nutritional danger posed by the inclusion of palm oil in a Western diet, nor, for that matter, is such a danger posed by diets that derive a high percentage of total fat from palm oil (Berger 1994; Ong, Choo, and Ooi 1994). In fact, when palm oil is added to a Western diet, the level of plasma HDL cholesterol typically rises, leading to a better LDL:HDL ratio, and this ratio - rather than the amount of total plasma cholesterol - appears to be the better indicator of the risk of coronary artery disease.

Palm oil can be fractionated to produce olein and stearin fractions; when heated to about 28° C, some 25 percent of the total remains solid (palm stearin). The liquid fraction (palm olein) has a greater unsaturated fatty acid content and can be further fractionated at 20-22° C (facilitated by the addition of a solvent) to yield a more liquid fraction, as well as an intermediate one. The fatty acid compositions of palm olein and palm stearin are shown in Table II. E.1.8. These fractions can be used for particular applications; for example, palm olein is commonly added to infant formulas because of its high oleic acid content. Plastic fats containing zero trans fatty acids are developed by interesterifying palm stearin and a more saturated fat, such as palm kernel oil. Palm olein has been used as a frying medium and has excellent stability because of its low linoleic and linolenic acid content and high levels of tocopherols. Cocoa butter equivalents can also be developed by using intermediate palm oil fractions.

Sunflower Oil

The sunflower (Helianthus annuus) is a wildflower that originated in the Americas. It was taken to Spain in 1569 for ornamental use, but later was grown for its oilseeds, especially in Russia. Newer, high-oil strains of sunflower have been developed, with oil contents upwards of 40 percent, as compared with 20 to 32 percent for traditional varieties.

Sunflower oil has a naturally high level of linoleic acid and is low in linolenic acid. The fatty acid composition of sunflower oil is highly variable and depends on climate, temperature, genetic composition, stage of maturity, and even the positions of individual seeds on the head of the flower. As the temperature of a region of sunflower cultivation increases, the oleic acid content increases and that of linoleic acid decreases, although together they always comprise about 90 percent of the fatty acids in sunflower oil.

Table II. E.1.8. Fatty acid compositions (weightpercentage) in palm olein and stearin

A typical fatty acid composition in cold environments includes 14 percent oleic acid and 75 percent linoleic acid, whereas in warm environments, it is 50 percent oleic and 43 percent linoleic acid. Because most sunflowers are grown in moderate climates, however, the actual variation in sunflower oil composition is, as a rule, not as marked as it might be.

New varieties of sunflower oil have been developed with modified fatty acid compositions. The fatty acid composition of a sunflower oil high in oleic acid is shown in Table II. E.1.4. High-oleic sunflower oils originated in Russia in the mid-1970s as a result of selective breeding and mutagenesis. The original Russian high-oleic line, “Prevenets,” has been developed into sunflower lines that have a stable high-oleic acid composition minimally affected by growing temperature (Morrison, Hamilton, and Kalu 1994). The high-oleic acid and low-linoleic acid composition makes the oil very suitable for frying, and the oxidative stability of products fried in high-oleic sunflower oil is excellent. However, flavor quality has been reported to suffer if the linoleic acid level is too low.

Crude sunflower oil contains a number of nontriglyceride components, including waxes, sterols, hydrocarbons, and tocopherols. Waxes, which create problems because they produce clouding of the oil, are removed in a process whereby the oil is cooled and the solids that develop are filtered off. The toco-pherols in sunflower oil consist primarily of alpha-tocopherol, which is good from the viewpoint of human nutrition because this tocopherol is the most biopotent form of vitamin E. However, tocopherols stabilize oils from oxidation, and the gamma and delta forms are much more active antioxidants in vitro than the alpha. In sunflower oil, the low levels of these tocopherols produce a lower-than-expected oxidative stability when compared to other vegetable oils with a higher degree of unsaturation.

Rapeseed (Canola) Oil

Rapeseeds include a number of closely related species in the genus Brassica. The three main species (Brassica nigra, B. oleracea, and B. campestris) have been manipulated by hybridization and chromosome doubling to produce B. napus, B. carinata, and

B. juncea. The different Brassica species have different seed sizes, colors, oil contents, and proximate compositions. The term “rapeseed” is used for any oilbearing Brassica seed, including that of mustard. Common names for some rapeseed species are shown in Table H. E.1.9.

The use of rapeseed oil for food and illumination originated in Asia (later spreading to the Mediterranean and Europe), and today, it is the most widely used cooking oil in Canada, Japan, and some other countries. Cultivated in India at least 3,000 years ago, rapeseed was introduced into China and Japan by the time of Christ. By the thirteenth century, rapeseed was cultivated for oil in Europe - especially eastern

Europe - and recently, it has been grown in Canada and the United States. Its first use was probably as an oil for lamps and lubrication; in addition, the nourishing oil cake residue of rapeseed makes a good feed for cattle.

Research in the 1960s showed that the erucic acid found in rapeseed oil caused fatty infiltration of the heart and changes in the cardiac muscle in experimental animals. The oil was therefore banned in many places, and although subsequent work showed that rapeseed oil presented no threat to human health, there were intensive efforts to develop low-erucic acid cultivars of the plant. In 1985, the U. S. Food and Drug Administration (FDA) conferred a GRAS (“Generally Recognized As Safe”) status on rapeseed products; not only was the oil deemed safe, but because of its very low content of saturated fat, it suddenly became viewed as the most healthy of cooking oils. Following the GRAS designation, U. S. production increased greatly, from 27 million pounds in 1987 to almost 420 million by 1994 (Trager 1995). In addition to its own production, the United States imports huge amounts of the oilseeds from Canada, although the end product’s name was changed, understandably, from rapeseed to Canola oil.

Recent developments in rapeseed breeding have resulted in seeds that are modified in fatty acid composition, and low-erucic acid rapeseed (LEAR) oils have been produced by Canadian breeding work with B. napus and B. campestris (Table II. E.1.4). Doublelow oils also are low in glucosinolates and include Canola (formerly Canbra) oil. To be considered a Canola or LEAR oil, the erucic acid content must be lower than 3 5 percent, although typically the level is less than 1 percent.

Canola oils are similar to soybean oils in that they contain appreciable levels of linolenic acid. Although some other vegetable oils have higher levels (for example, oils from flax seed or linseed contain about 55 percent linolenic acid), these are not common in the diet and are subject to very rapid rates of oxidation. In no small part because it has the lowest saturated fat content of any major cooking oil, Canola has been called an ideal mixture for health, nutrition, and food use (Ackman 1990).The oil has high amounts of oleic acid, reasonably low linoleic acid, and a moderate omega-6 to omega-3 ratio. The high-oleic level is beneficial nutritionally, as oleic acid tends to lower LDL cholesterol, with no drop - and even a slight increase - in HDL cholesterol, resulting in a net positive change in the HDL:LDL ratio.

Peanut Oil

The peanut or groundnut (Arachis hypogea), like the bean, is a member of the family Leguminosae. It is native to South. America, probably originating in or around lowland Bolivia, but as early as 3100 to 2500 B. C., peanuts were common on the coast of Peru, and by the time of the Columbian voyages, they had spread throughout much of the New World (Coe 1994). In the sixteenth century, the peanut was carried to West. Africa from Brazil by Portuguese traders, and because it was first brought to the United States from West Africa in slave ships, the misconception arose that the plant was of African origin.

While the Portuguese moved the peanut eastward, the Spaniards carried it west. It was introduced into the Philippines by Ferdinand Magellan and spread thereafter to other parts of Asia. Peanuts can be grouped into four different types: Runner, Spanish, Vir-ginia, and Valencia. Runner peanuts are small and high yielding, Spanish are small seeded, and Virginia are large seeded. Valencia are large seeded and are often found with 3 to 5 seeds per pod.

Normal peanut oil has almost no linolenic acid and about 25 percent linoleic acid. As a rule, it contains about 50 percent oleic acid and is considered a premium oil for food use because of its excellent stability and its pleasant, nutty flavor. As with some other oilseeds, temperature affects the fatty acid composition, with cool climates resulting in greater linoleic and lower oleic acid levels. High-oleic peanuts were developed at the University of Florida during the 1980s and have subsequently become commercially available. A typical fatty acid composition of a high-oleic peanut oil is shown in Table n. E.1.4. Peanut oil, including the high-oleic variety, is characterized by relatively high levels of long-chain saturated fatty acids (up to 6 percent), up to and including 26:0. High-oleic peanut oil is between 7 and 10 times more stable in the face of oxidation than normal peanut oil (O’Keefe, Wright, and Knauft 1993), and roasted high-oleic peanuts have about twice the shelf life of normal peanuts (Mugendi, Braddock, and O’Keefe 1997; Mugendi et al. 1998).

P J. White (1992) has pointed out that in the past, peanut oil was wrongly reported to contain significant levels of linolenic acid because of the mistaken identification of 20:0 or 20:1 ra9 as linolenic acid. Depending on analytical conditions, it is possible to have coelution of linolenic and 20:0 or 20:1 ra9. Similarly, reports exist in which arachidonic acid (20:4ra6) has been mistakenly identified in vegetable oils, but, in fact, arachidonic acid has never been found in vegetable oils.

Cottonseed Oil

Cotton (any of the various plants of the genus Gossyp-ium) has been grown for its fiber - used in the manufacture of rope and textiles - for close to 5,000 years. Doubtless, in the distant past, the oil-rich cotton seeds were also utilized for illumination, as a lubricant, and probably for medicinal purposes. Indeed, most of the vegetable oils seem to have been first utilized for such nonfood applications.

The widespread use of cottonseed oil, however, is a relatively recent phenomenon that began in the United States. Some of the oil is derived from the extra-long staple G. barbadense, but the overwhelming bulk of the world’s production (90 to 98 percent) comes from the short staple G. hirsutum, and short-staple cotton had to await the invention of the cotton gin by Eli Whitney in 1793 to become commercially viable. Thereafter, short-staple cotton spread across the southern United States, and surplus seed was converted into oil. Initial attempts at commercialization, however, were unsuccessful: Unlike long-staple cotton, the short-staple species had a tough seed coat that retained lint.

This problem was resolved in the middle 1850s with the invention of a machine to crack the hulls. High oil prices encouraged cottonseed oil extraction, and in the late 1880s, the Southern Cotton Oil Company was founded in Philadelphia. Its many seedcrushing mills, located throughout the South from the Carolinas to Texas, made it the largest producer of cottonseed oil, as well as the first U. S. manufacturer to make vegetable shortening.

One problem that remained was the odor of cottonseed oil, but this was eliminated at about the turn of the twentieth century with a deodorizing process invented by the company’s chemist David Wesson. The procedure involved vacuum and high-temperature processing and led to the production of Wesson Oil, which revolutionized the cooking-oil industry (Trager 1995). Thereafter, cottonseed oil became the first vegetable oil to be used in the United States and then the dominant oil in the world’s vegetable oil market until the 1940s.

Cottonseeds contain gossypol, which is produced in the seed glands and must be removed or destroyed in both oil and meal. Gossypol is heavily pigmented and can produce a dark color in the oil, and it is also toxic. Fortunately, it can be almost completely removed during the refining process, and in addition, glandless seeds devoid of gossypol have been developed.

Crude cottonseed oil contains as much as 1 percent of cyclic fatty acids. The main fatty acids are mal-valic and sterculic, which are present in the form of glycerides. Cottonseed oil is characterized by a high saturated fat level, which is much higher than that of corn, canola, soybean, sunflower, peanut, and safflower oils.

Coconut Oil

The coconut palm (Cocos nucifera) has been enthusiastically described as the “tree of life” or the “tree of heaven” because it provides leaves and fiber for the construction of dwellings and shells for utensils, as well as food, milk, and oil. Although the coconut palm has been exploited by humans for millennia, its origin is subject to debate, with some scholars claiming it to be native to South America and others supporting a Southeast Asian origin. The question is a difficult one because coconuts can still germinate after floating on the ocean for months, a capability which has facilitated their spread throughout the tropical world. Compared with other oilseed crops, coconuts have a high per-acre yield of oil, about half of which is used in nonfood applications (such as soaps and cosmetics), whereas the other half goes into foods.

Coconut oil is extracted from the dried meat of the nuts (copra). Copra has one of the highest fat contents of all the materials used for oil (Table II. E.1.1), making it easy to obtain oil by pressing. Coconut oil contains high levels of the medium chain saturated fatty acids (10:0, 12:0, and 14:0) and is solid at room temperature.

The saturation of coconut oil confers a high degree of stability toward oxidation, but hydrolysis of coconut oil to yield free fatty acids causes soapy off-flavors because of the free lauric acid present. Fatty acids longer than lauric acid, however, produce little or no off-flavor.

Animal Fats and Oils Milkfat (Butter)

Milkfats are derived from any number of different animals, but most by far is provided by the bovine; consequently, in this chapter, milkfat means that from cows. A lactating cow can produce as much as 30 kg of milk per day with a milkfat level of 2.6 to 6 percent, and thus for many years, butterfat was produced in greater quantity than any other fat or oil.

Milkfat, which has a much more complex composition than any of the other common fats, contains about 97 to 98 percent triglycerides, 0.1 to 0.44 percent free fatty acids, 0.22 to 0.41 percent cholesterol, and 0.2 to 1.0 percent phospholipids. More than 500 different fatty acids have been identified in milk lipids. The fatty acid patterns in milkfat are complicated by mammary synthesis of short-chain fatty acids and extensive involvement of rumen bacteria in lipid synthesis and modification (Jensen 1994). As a rule, butterfat is predominantly composed of palmitic acid, followed by oleic and myris-tic acids (Table II. E.1.10). About 66 percent of the fatty acids in a typical milkfat are saturated. The trans fatty acid levels in milkfat have reportedly ranged between 4 and 8 percent.

Table II. E.1.10. Fatty acid composition of butterfat (weight percentage)

There has been a great deal of interest over the past 30 years in modifying the fatty acid composition of butterfat to decrease the saturated fat content (Sonntag 1979b). Because cows have a rumen, fats that are directly provided in the diet are extensively degraded and hydrogenated. The fat also can have negative effects on the rumen bacteria, causing a lowering of milk and milkfat production. This problem has been solved by providing “protected” fats to the animal.

Methods of protecting fats from rumen metabolism include the polymerizing of protein around fat with formaldehyde and the preparation of calcium soaps, which are mostly insoluble at rumen pH. Dairy fats with high linoleic acid contents have been developed, but they suffer from severe quality problems and are unmarketable (McDonald and Scott 1977).

Recently, dairy fats have been prepared with high oleic and low saturate composition by feeding a calcium salt of high-oleic sunflower oil (Lin et al. 1996a, 1996b). This has provided lower saturated fatty acid composition and higher monoene while maintaining product quality. Oleic acid oxidizes about 10 times more slowly than linoleic acid and provides a better health benefit.

Marine Fats

Marine fats and oils, which are among the oldest exploited by humans for food and other uses, are divided into those from fish (cod, herring, menhaden, sardine, and so forth), from fish livers (cod, shark, halibut), and from marine mammals (whales). Marine oils are characterized by a very complex composition compared to vegetable oils and many animal fats, which poses challenges in the accurate identification and quantification of their fatty acids. Moreover, data derived from old technology may not be accurate.

Figure II. E.1.5- Effects of overfishing in Pacific sardine fishery, 1918-60.

Fish oils. Fish oils are obtained from tissues that contain a high fat content, including those of herring, pilchard, menhaden, and anchovy. The production of the various fish oils is dependent on both fishing efforts and overfishing. In Figure II. E.1.5, it can be seen that the Pacific sardine fishery was extremely successful for about 20 years, after which the fish stocks were depleted so that a fishery could no longer be supported. It is sad to note that this is the rule rather than the exception in many fisheries worldwide.

Early production methods consisted of boiling the fish in water, followed by pressing, and then removing the oil by skimming. Improved oil quality and recovery was obtained as steam cooking and screw presses were introduced. Much of the fish oil produced in earlier days went into nonfood uses, such as linoleum, paints, and soaps.

Currently, oils from marine sources constitute some 2 to 4 percent of the world’s consumption of fats, and about one-third of the world’s fish catch consists of small and bony but high-fat fish that are converted into fish meal and oil. Fish oils for food use are often partially hydrogenated because they oxidize rapidly in comparison with vegetable or animal fats and oils. Partial hydrogenation results in a loss of polyunsaturated fatty acids, monoenes, dienes, and trienes, which obviously has negative effects on the nutritional value of hydrogenated oils. Because of the interest in omega-3 fatty acids found in fish oils, recent work has focused on the incorporation of processed, but not hydrogenated, fish oils in food products.

Fish liver oils. The livers of some fish have a high fat content and are rich in vitamins A and D. Although many different species of fish (for example, pollock, haddock, shark, halibut) have been exploited for their liver oils, the cod has provided more than 90 percent of the total volume. Cod livers contain from 20 to 70 percent fat; the range is so great because codfish deposit fat prior to spawning and deplete it during spawning. Thus, there is a cyclical fat content in their livers, and this has a dilution effect on the levels of the fat-soluble vitamins.

Cod liver oil was reportedly used for medicinal purposes in the eighteenth century, long before the discovery of vitamins or an understanding of most nutritional diseases. Medical uses included treatment of bone afflictions, rheumatism, tuberculosis, and, later, rickets. There was an intensive search for the active ingredient in cod liver oil that caused such positive therapeutic effects. The hunt was described by F P Moller (1895:69):

The oldest of these active principles, iodine, was detected as one of the oil’s constituents as far back as 1836. . . . When the iodine active principle was exploded another, trimethy-lamine, took its place, and as a result herring brine, from being a rather neglected commodity, became for a short time the desideratum of the day. After a quick succession of other active principles, too evanescent to be worthy of even an obituary notice, the turn came for the free fatty acids. No theory and no fact then supported the idea that these acids were the active principle.... Still, the belief entered some active mind that they were the essential constituents.

Moller concluded incorrectly that there was no specific active principle in cod liver oil. Yet, liver oils provide fat-soluble vitamins. However, when consumed at the levels required to derive significant health benefit from the fatty acids present in fish liver oils, there is a risk of hypervitaminosis A or D.

The levels of fat-soluble vitamins in various fish liver oils are shown in Table II. E.1.11. Excessive levels of both vitamins A and D3 can be toxic. Although the actual value is not clear, as little as 50 micrograms of vitamin D3 per day over extended periods appears to produce toxicity symptoms in humans (Groff, Gropper, and Hunt 1995). Daily levels of 250 micrograms for several months have resulted in soft-tissue calcification, hypertension, renal failure, and even death. The recommended daily intake of vitamin D is 5 to 10 micrograms. The vitamin D level in fish oils ranges up to 750 micrograms per gram. Obviously, extended daily use of a high-potency fish oil should be avoided. Cod liver oil, which constitutes the majority of all liver oils sold today, has modest but nutritionally significant levels ranging up to 7.5 micrograms per gram.

The recommended daily intake of vitamin A is 1,000 retinol equivalents. One retinol equivalent is equal to 1 microgram of all-trans retinol. Toxicity is seen at levels around 10 times greater than the RDA, so that a daily intake of 10 mg of all-trans retinol would result in toxic symptoms. Symptoms of toxicity include itchy skin, headache, anorexia, and alopecia. The extremely high vitamin A levels in some liver oils would make it fairly easy to consume toxic amounts of vitamin A.

Whale oils. Whale oils are derived from marine mammals. The worldwide production of whale oils has decreased as populations of whales have been depleted. Oils from the baleen whales (sei, right, blue, humpback, and minke), as well as toothed and sperm whales, have been employed in industrial applications and human food use. Sperm whales (Physeter macro-cephalus), in particular, were prized in the past for their “spermaceti” oil, which was used in smokeless lamps, as a fine lubricant, in cosmetics, and in automatic transmission oils. One sperm whale could yield 3 to 4 tons of spermaceti.

Table II. E.1.11. Fat-soluble vitamin levels in fish liver oils

Whale oils saw food use in some, but not all, countries when whale harvests were high. Europe, Canada, and Japan, for example, utilized hydrogenated whale oil in margarines for almost 50 years. During that time, the production of fish oils was much lower, increasing only as the production of whale oil decreased. Whale oils were also employed in the manufacture of shortenings after hydrogenation, a process which results in the production of many trans fatty acid monoene isomers.

Conclusion

The types and amounts of fats and oils that have been consumed vary greatly worldwide among people and have changed significantly over the past century. Fatty acid intakes will undoubtedly change in the future as oilseeds with altered fatty acid compositions reach new markets.

Sean Francis O’Keefe

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