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Oils and fats
David S. Seigler Department of Plant Biology University of Illinois Urbana, Illinois USA
OUTLINE: OILS AND FATS Importance o All cultures o Required in diet Botanical o Many families Economics o Multiple plant use o Press-cake
Chemistry o Triglycerides o Short vs long chain fatty acids o Unsaturated vs saturated fatty acids o Soaps-saponification o Polymerization - paints + Non-drying + Drying + Semi-drying o Precursors for plastics o Petroleum substitute
Isolation o Extraction methods o Crushing/expression
Reading CHAPTER 9 IN THE TEXT
Introduction Oils (liquid) and fats (solid) common and important items in the diet of humans. Most of the ones we use come from seeds (or animals). The use of seed oils is ancient.
In contrast to essential oils, these substances are made up of triglycerides and are not volatile. Triglycerides contain fatty acids and glycerol. The structures of the fatty acids determine many of the properties of the oils and fats.
Triglycerides are a food reserve for the germinating embryo. Similar oils and fats are obtained from animals. In general, the longer the chains of the fatty acids, the higher boiling the oils or fats are. Peanut oil has lots of C 20 fatty acids and is high boiling.
Sites of unsaturation lower the boiling point and increase the sensitivity to oxygen. The oils with 2 or 3 sites of unsaturation polymerize readily and have often been used in paints.
The properties of highly unsaturated oils that make them valuable also make them undesirable for food products because they tend to turn rancid readily. Unsaturated oils can be converted to saturated oils by hydrogenation with a catalyst (usually nickel). This raises the melting point. Originally done by Wesson. Pg. 221.
Non-drying-saturated- typically tropical plants palm, peanut, olive, rape, castor, almond Drying oils-highly unsaturated (polyunsaturated) linseed, tung, soy bean, hempseed, nut, poppy, safflower Semi-drying oils (moderately unsaturated) cottonseed, sunflower, sesame, croton, corn. Many important oils are listed on page Many seeds contain quite large quantities of oils. Sesame seed, for example, is more than half oil.
Extraction methods The seeds are usually cleaned and then dehusked. Crushing - today done mostly with rollers. A screw press makes it possible to have a continuous feeding of seeds. The oil flows out (pg. 229, 227). Because there is still 2-4% oil in the meal, the material is extracted again with solvents in some cases. In some cases, the kernels are broken or flaked before extraction.
Expression - cold and hot (where seeds are cooked first). For an outline of the complete process, see pg Extraction - solvents (petroleum ether (hexane), chlorinated solvents). Boiling - centrifugation
Subsequent treatment of oils After isolation, the oils are treated for several reasons. In many cases, the oils are treated with caustic soda to remove any free fatty acids present. The oil may then be degummed, bleached, deodorized, and/or winterized. Degumming is done by mixing the oil with water and centrifuging.
Bleaching is usually done with Fuller's earth or activated charcoal. Deodorizing is often done with steam. Winterizing is cooling down the oil and removing materials that precipitate out. The fatty acids and triglycerides that precipitate out are called "foots". Most oils are treated to render them odorless and tasteless (and interchangeable).
Almost all oils and fats come from seeds (except for olive and avocado). They are required in the diet of most animals. Margarine and shortening are made by hydrogenation. Uses of fats and oils
Lubricants Soap - now largely replaced by synthetic detergents Paints - now largely replaced by synthetic polymers. Chemical precursors - nylon, polymers - probably the best petroleum substitute. Press cake is usually used for livestock feed Biofuels
Table pages Linseed oil This is probably the oldest domesticated oil seed crop. Flax or linseed (Linum usitatissimum, Linaceae) is from the Near Eastern Center. Fossil linseed shows signs of selection by 6000 B.C. In the time of the Egyptians, coffins were painted with mixtures of linseed oil and resin. The plant is also used for fiber. Major oilseed crops
Linseed oil alone still used to finish many wood products. Linseed oil is used as an edible oil in some parts of the world, but has largely been replaced by other oils. Flax seed a major source of omega-3- fatty acids and may be valuable in human diets.
Flax in the Pampas of Argentina
Flax, Linum usitatissimum, Linaceae
Tung oil, Aleurites fordii, Euphorbiaceae Tung oil is mostly from China. This small tree has fruits that contain a highly unsaturated but inedible oil. Tung oil one of the best quality furniture finishing oils. The press cake is highly toxic.
Tung, Aleurites fordii, Euphorbiaceae
Safflower oil, Carthamus tinctorius, Asteraceae or Compositae Safflower oil is unsaturated and is considered to be a good quality salad oil. Safflower was domesticated in the Mediterranean area. This species is only known in cultivation. Safflower was probably first grown for the yellow dye it produces.
Safflower, Carthamus tinctorius, Asteraceae
Soybeans (Glycine max) Soybeans are, of course, an ancient crop as previously described. In the Orient they are not usually used for oil purposes. Europeans began to press them back in the 1700's. Today, almost all soybeans used in the U.S. are pressed for oil. The soybean is about % oil. The press cake is used for feeding livestock and as a human food additive.
Glycine max, soybean
The sunflower was domesticated about 5000 years ago in Mexico and has become a major crop. The seeds were widely eaten by the American Indians. The crop was highly modified in Europe, however. It is an especially an important crop in the former Soviet Union. Sunflower (Helianthus annuus) Asteraceae
Sunflowers, Helianthus annuus, Asteraceae
The cultivated types of sunflowers today are much larger than the wild ones. The plant is still a common weedy species in much of the Midwest. See sunflower diagram on pg. 234.
Corn or maize (Zea mays) Corn, of course, is cultivated for other purposes, but also for oil. The oil is a minor by-product of corn milling to isolate starch. The corn is steeped in sulfurous acid and then lightly macerated to separate the embryo from the endosperm. Diagram pg The oil is isolated from the embryos. Most refined corn oil used for margarine and salad oils.
Carolina Biological Supply Co.
Sesame (Sesamum indicum, Pedaliaceae) Sesame oil an ancient crop. It probably arose in India. On the other hand, the close relatives of sesame are mostly from Africa. The oil has a relatively strong flavor and is much used in Chinese cooking. Sesame oil commonly used in Africa, the Middle East, India, and China. The seeds themselves are also widely eaten.
Sesame, Sesamum indicum, Pedaliaceae Courtesy Dr. Dorothea Bedigian
Cotton (Gossypium hirsutum, Malvaceae) Cotton widely grown for fiber. The seeds used as a source of edible oil for thousands of years. Cotton seed contains a toxic compound, gossypol. A problem in utilizing the press cake. David Wesson's process of purification with caustic soda, steam and fuller's earth removed much of the gossypol. Shortening was first made by hydrogenation of cottonseed oil.
Cotton, Gossypium hirsitum, Malvaceae
Cotton field and cotton boll
Rape or canola, Brassica napus, Brassicaceae or Cruciferae Rapeseed or canola commonly grown in Canada and in Europe. The oil used for both a lubricant and as an edible oil. It is largely used to make margarine in Europe. Selection for low erucic acid lines (canola) for edible purposes and cultivation of erucic acid lines for lubricant purposes. The press cake of limited value for feeding livestock.
Canola, Brassica napus, Brassicaceae or Cruciferae, in Ontario Courtesy Dr. Clint Chapple
Flax and canola in Manitoba Courtesy Dr. Ellis McLeod
Rapeseed in Germany
Peanut oil, Arachis hypogaea, Fabaceae or Leguminosae Peanut oil widely used in the tropics. It is especially common in Africa and in France. Peanut oil higher boiling than most other oils and imparts a pleasant taste to the food.
Arachis hypogaea, peanut in flower
Pollinated ovary going under the soil
Primitive peanut relative - Arachis villosa
Olive oil (Olea europaea, Oleaceae) Olive oil is another ancient crop from the Near East. At least 3500 B.C. in Crete. Olive oil was also used as a cleanser, for annointing, as a lamp oil, for medicine, and as a food stuff. Olive oil comes from both the fruit pulp and from the seed. There are many different grades of olive oil.
Olives, Olea europaea, Oleaceae
Castor bean (Ricinus communis, Euphorbiaceae) Castor bean probably grew in both Asia and Africa when it was domesticated. Seeds at least 6000 years old have been found in Egyptian tombs. The oil was probably used in medicine and as a lamp oil. Castor oil is also a precursor for plastics.
Castor bean (Ricinus communis, Euphorbiaceae)
Castor oil is still used as a laxative. The seeds are highly toxic but the compounds responsible are not soluble in the oil. Pg Today most castor oil is used for soaps, paints, and Turkey red oil. It is also used widely as a lubricant. The press cake is too toxic for any use except fertilizer.
Palm and palm kernel oils Oil palms (Elaeis guineensis, Arecaceae) differ from most other oil seeds in that both the fruit pulp and the seed are used. Actually a series of palms are used. Another one is Oribignya oleifera (native to S. America). There is also a comparable Asian species.
African oil palm (Elaeis guineensis, Arecaceae) National Geographic
The African oil palm is probably the most widely cultivated today. Pg The plant is only semicultivated. The fruits are harvested when ripe. Most consumers in isolated, rural areas make their own oil by boiling the fruits and collect the oil as it floats to the top. Commercially, the fruits are pressed quickly after cooking with steam. The kernels are extracted later. Palm oils are used for soap and candles, but also in margarine and for shortening.
Cooking dende oil from oil palms Courtesy Axel Walther
Coconut oil is isolated from copra, the “meat” that is removed from the seeds and dried. Coconuts are widely used in the tropics for just about everything. Coconuts originated in southeastern Asia. In the 1800's, people started to use coconut oils to make soap. Coconut oil also mixes with many other oils and has a pleasant taste. Coconuts (Cocos nucifera, Arecaceae)
Extracting copra from coconuts in Oceania Courtesy Dr. S. Glassman
The press cake also used as a cattle feed. Coconut oil used in shampoos, hand lotions, suntan creams, non-dairy products, cosmetics.
Other oilseeds In some countries, crambe (Crambe abyssinica, Brassicaceae or Cruciferae) is used. It is similar to rape seed oil. Grapeseed oil (Vitis vinifera, Vitaceae) is used in countries where grapes are commonly grown for wine making. Hempseed oil (Cannabis sativa, Cannabaceae) oil is used in some Near Eastern countries.
Niger seed, Guizotia abyssinica, Asteraceae
Shea butter tree, Butyrospermum parkii, Sapotaceae The fats from the fruits are used as a food in West Africa and in cosmetics worldwide
Soap Soaps are the salts of fatty acids. Potassium and sodium soaps are the most commonly used. Magnesium and calcium soaps are found as bathtub ring. Lead and zinc are used to make medicinal soaps Lithium soaps are used to make lubricants. Aluminum soaps are used for waterproofing.
Device for isolating “caustic” potassium carbonate from wood ashes
Oils and fats are treated with lye (sodium hydroxide or potassium hydroxide) to yield salt of the fatty acids. Formerly, extracts of wood ashes were used. Potassium gives soft soaps and sodium gives hard soaps. Detergents often made by sulfonation of other types of organic molecules. Saponins from plants used in some societies as soap or detergent substitutes. Coconut oil is still the most commonly used oil for soap.
Paints Many polyunsaturated oils are incorporated with pigments into paints and varnishes. Linseed oil and tung are among the most common of this type. The Flemish combined pigments and oils to make oil paints in the 15th century. They perfected technique of painting over the pictures with glazing, and translucent coatings over an undercoating in order to give an illusion of depth. Pg. 223.
Vegetable oils are heated with heavy metal salts to catalyze polymerization before being used in paints. These help the oil to absorb oxygen. Varnishes also include resins. In general, today, people have shifted to water-based paints.