Oils (liquid) and fats (solid) are common important items in the diet of man. Most of the ones we use come from seeds. The use of seed oils is ancient. In contrast to essential oils, these are made up of glycerides and are not volatile.
Glycerides contain fatty acids and glycerol. The structures of the fatty acids determine many of the properties of the oils and fats.
They are the food reserve of 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 C20 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.
There is some evidence that highly saturated oils (ones that lack sites of unsaturation) are not too good for you. There is other evidence that highly unsaturated oils (those with lots of sites of unsaturation) are also not too good.
Probably the most important part is that as Americans, we eat too many lipids.
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. Some of the chemical features are diagrammed on page 221.

Sesame seeds

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 230-231.
Many seeds contain quite large quantities of oils. Sesame seed, for example, is more than half oil.

Extraction methods
Crushing - today done mostly with rollers. A screw press makes it possible to have a continuous feeding of seeds. The oil flows out also (see the diagram on page 229, 227).
Because there is still 2-4% oil in the meal, the material is still extracted with solvents in some cases. The seeds are usually cleaned and then dehusked. 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 page 229.
Extraction - solvents (petroleum ether, chlorinated solvents).
Boiling - centrifugation

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 that precipitate out are called "foots".
Most oils are treated to render them odorless and tasteless (and interchangeable).

Uses of fats and oils
The oils and fats serve as food for the plant. Almost all come from seeds (Except for olive and avocado). They are required in the diet of most animals Margarine and shortening are made by hydrogenation
Soap - now largely replaced by synthetic detergents
Paints - now replaced to some extent by synthetic polymers Formerly linoleum. Today replaced by substitutes.
Chemical precursors - nylon, polymers - probably the best petroleum substitute Press cake is usually used for livestock feed

Major Oilseed crops

See the table on pages 230-231.
Linseed oil
This is probably the oldest domesticated oil. Flax or linseed (Linum usitatissimum, Linaceae) is from the Near Eastern Center. Fossil linseed shows signs of selection by 6000 B.C.
The plant is also used for fiber. In the time of the Egyptians, coffins were painted with mixtures of linseed oil and resin.
Linseed oil alone is 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.
Tung oil
Tung oil is mostly from China. The small tree, Aleurites fordii, Euphorbiaceae, has fruits that contain this highly unsaturated and inedible oil. This is one of the best quality furniture finishing oils. The press cake is highly toxic.

Flax seed
Flax flowers

Safflower oil
Safflower oil is unsaturated and has been considered to be a good quality salad oil. It comes from Carthamus tinctorius, Asteraceae or Compositae, and was also domesticated in the Mediterranean area. The species is only known in cultivation.
Safflower was probably first grown for the yellow dye it produces.

Soybean oil
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 press cake is used for feeding livestock and as a human food additive. The soybean is about 13-25% oil.

Soybeans in the field

Sunflower oil
The sunflower is one of the few North American plants that has been domesticated and has become a major crop. The seeds were widely eaten by the American Indians. The crop was domesticated in Europe, however.
This is an especially an important crop in the former Soviet Union. The cultivated types of today are much larger than the wild ones. The plant is still a common weedy species in much of the midwest.
See the sunflower diagram on page 234.


Corn oil
Corn, of course, is cultivated for other purposes, but also is used for oil. The oil is a minor by-product of the corn milling oil. The corn is steeped in sulfurous acid and then lightly macerated to separate the embryo from the endosperm.
See the diagram on page 235.
The corn is isolated from the embryos. Most refined corn oil is used for margarine and salad oils.

Sesame oil
Sesame (Sesamum indicum, Pedaliaceae) is another 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.
It is commonly used in Africa, the Middle East, India, and China. The seeds themselves are also widely eaten.

Cottonseed oil
Cotton (Gossypium hirsutum, Malvaceae) is widely grown for the fiber. The seeds have also been used as a source of edible oil for thousands of years. However, cotton seed contains a toxic compound, gossypol, that is 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 compound. Shortening was first made by hydrogenation of cottonseed oil.

Cotton bolls

Rapeseed or canola oil
Rape or canola (Brassica napus, Brassicaceae or Cruciferae) is commonly grown in Canada and in Europe. The oil has been used for both a lubricant and as an edible oil. It is largely used to make margarine in Europe.
There has been selection for low erucic acid lines (canola) for edible purposes and cultivation of erucin acid lines for lubricant purposes. The press cake is of limited value for livestock purposes.

Mustard in the field

Peanut oil
Peanut oil from Arachis hypogaea( Fabaceae or Leguminosae) is widely used in the tropics. It is especially common in Africa and in France. It is higher boiling than most oils and imparts a pleasant taste to the food.

Olive oil
Olive oil (Olea europaea, Oleaceae) 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.

Castor oil
Castor oil (Ricinus communis, Euphorbiaceae) is still used as a laxative. The seeds are highly toxic but the compounds responsible are not soluble in the oil. See the diagram on page 239.
Castor bean probably grew in both Asia and Africa when it was domesticated. Seeds have been found in Egyptian tombs at least 6000 years old. The oil was probably used in medicine and as a lamp oil. Castor oil is also a precursor for plastics.
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 e.g. Oribignya oleifera (native to S. America). There is also a comparable Asian species.
The African oil palm is probably the most widely cultivated today. See the diagram on page 240. 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.

Coconut oil
A very similar oil is isolated from copra from coconuts (Cocos nucifera, Arecaceae). They are widley used in the tropics for just about everything. They originally came from southeast Asia. The meat is removed and dried.
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. The press cake is also used as a cattle feed. Coconut oil is also used in shampoos, hand lotions, suntan creams, non-dairy products, cosmetics.

Other oil seeds
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.
Oiticica oil (Licania rigida, Rosaceae) from Brazil is used for paints. It contains a special type of fatty acid (keto fatty acids) (55-62%).
Poppyseed oil is used in a number of Asian countries.

Soaps are the salts of fatty acids. The most common soaps used by man are potassium and sodium. Magnesium and calcium soaps are found as bathtub ring. Lead and zinc are used to make medicinal soaps and lithium is used to make lubricants. Aluminum soaps are used for waterproofing.
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 are made by sulfonation of other types of organic molecules usually.
Saponins from plants are often used in some societies as soap or detergent substitutes.
Coconut oil is still the most commonly used oil for soap.

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 also perfected technique of painting over the pictures with glazing, and translucent coatings over an undercoating in order to give an illusion of depth.
See the diagram on page 223.
Many good enamels contain perilla oil (Perilla ocymoides, Lamiaceae or Labiatae). The seed is about 38% oil. 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. Many of these are still made from materials from seed oils. Alkyd resins are polymeric materials made from fatty acids.

Lecture slides for Oils and Fats


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Revised March 2005

© David S. Seigler, Integrative Biology 363, Plants and Their Uses, Department of Plant Biology, 265 Morrill Hall, 505 S. Goodwin Ave., University of Illinois, Urbana, Illinois 61801, USA. 217-333-7577. seigler@life.uiuc.edu.