Oils, waxes, resins, gums, latex

Food oils are mainly pressed from seeds. Lipids are a major component of the endosperm of coconuts, and the cotyledons of soybeans, peanuts, canola and cotton, all major sources of plant oils

In monocots like maize, lipids are a major component of the scutellum (the single cotyledon of grasses).

An exception is olive oil, which is obtained from the olive fruit (a drupe).

Plant oils are used as food but increasingly are being used for other purposes.Plant oils have long been used as soaps and cleaning. More recently plant oils have been used as the basis for manufacturing plastics and foam used for building insulation.

Chemistry of Plant Oils

Lipids are a large group of molecules that are important components of living cells. Lipids include fats, oils, sterols, certain vitamins, and are the main components of the bilayer membranes of cells. The common characteristic of lipids is that they are insoluble in water.

Plant oils almost exclusively belong to one chemical group: acylglycerides

Acylglycerides consist of a glycerol molecule “backbone” to which one, two, or three fatty acid molecules are attached. Most plant oils are mainly triglycerides.

Acylglycerides

Monoglycerides are glycerol molecules with one fatty acid group.Monoglycerides are not important components of oils, but polymers of monoglycerides are the main constituent of cutin, the outer covering layer of waxy leaves, and suberin , the hydrophobic component of the casparian strip and phellem (cork) cells.

Diglycerides are minor components of plant oils, about 1-6%.

Triglycerides are the major component of plant oils.

The chemical properties of the triglycerides depends on the type of fatty acid molecules attached to the glycerol backbone.

A fatty acid is also a type of lipid that consists of a hydrocarbon chain with a carboxyl (COOH) group at one end that defines the molecule as an organic acid. The carboxyl group of the fatty acid combines with the OH group of the glycerol molecule to form an ester bond.

Fatty acids vary in the length of the hydrocarbon chain and its degree of saturation.

Chemical properties of fatty acids depend on the length of the hydrocarbon chain and its degree of saturation.

Saturation means the number of double bonds in the fatty acid chain. A monounsaturated fatty acid has one double bone.

Saturated fats are solid at room temperature (e.g. butter), most vegetable fats are polyunsaturated and are liquid at room temperature.

Double bonds cause the hydrocarbon chain to bend, the regular structure of saturated fatty acids allows the molecules to form a regular order (crystallize) at room temperature. The irregular shapes of unsaturated fats cause them to resist crystallization, so they are liquid at room temperature.

Linoleic acid has 18 carbons

Stearic and oleic acids both have 16 carbons

Fatty acid composition of different plant oils.

Plant oils are mostly unsaturated (except palm oil and coconut oils) while animal fats have a high proportion of saturated fats.

Essential Fatty Acids

Essential fatty acids, like essential amino acids, are fatty acids that cannot be synthesized and so must be obtained from the diet.

Essential fatty acids are linoleic (two double bonds), linolenic ( three double bonds), and arachidonic (four double bonds) acids.

Essential fatty acids are required for synthesis of other fatty acids needed for cell functions, synthesis of hemoglobin, and a very important array of physiological interactions ranging from repair of cells to central nervous system functions.

Cholesterol and Fatty Acids

Cholesterol is another naturally occurring lipid (water insoluble compund) that belongs to the class of chemicals called sterols or steroids. Cholesterol is an essential component of animal cell membranes and is an intermediate in the synthesis of vitamin D and endocrine hormones.

There are two sources of cholesterol in the body: dietary intake and synthesis in the body itself.

Cholesterol is produced in the liver and transported in the blood from the liver to cells in the body where it is needed for cell functions. Cholesterol is also absorbed in the intestine when animal fats are consumed. Because cholesterol is not soluble in water, it is transported in the blood as a chemical complex with lipoproteins that help solubilize it.

LDL is low-density lipoprotein, HDL is high-density lipoprotein. HDL helps to eliminate excess cholesterol from the body, it transports the cholesterol to the liver where excess cholesterol can be broken down. HDL is “good cholesterol” because it helps to remove excess cholesterol from the body.

Cholesterol and Fatty Acids

LDL transports cholesterol to all the cells in the body. This can lead to atherosclerosis, “hardening of the arteries” , fatty deposits in the cells lining the arteries when cholesterol is deposited in the cells that line the arteries.

Atherosclerosis results from the accumulation of plaque, which is produced when cholesterol molecules oxidize and the oxidzed molecules are then engulfed by white blood cells (macrophages). Macrophages die after consuming a large amount of cholesterol and are deposited as plaque on the artery walls.

Diets rich in animal fat or saturated fats, and trans-fats from partially hydrogenated plant oils can increase body cholesterol levels, particularly LDL.

Polyunsaturated fats in the diet lower both LDL and HDL but monounsaturated fats increase HDL and lowe LDL levels. In addition, polyunsaturated fats have been linked to the production of free radicals, highly reactive molecules that are associated with increased risks of certain types of cancer.

Monounsaturated fats therefore are considered the most desirable source of fatty acids for a healthy diet.

Hydrogenated oils

Hydrogenated oils are made by adding hydrogen (by pumping hydrogen gas) into vegetabel oil. The hydrogen reacts with the unsaturated bonds causing the hydrocarbon chains to straighten. Hydrogenated oils are solid at room temperature.

Hydrogenation makes liquid vegetable oils solid or semisolid, so hydrogenation is used to make margarine

Hydrogenation also causes the remaining double bonds to change to the trans configuration. Trans-fats have been implicated in lowering HDL cholesterol and raising LDL cholesterol in humans, resulting in increased risk of coronary heart disease.

“Rancid” oil results when the double bonds of an unsaturated fat react with oxygen. This causes the molecule to split into smaller molecules that are volatile and foul-smelling. Antioxidants (BHA, BHT, polysorbate) are added to processed foods to prevent oils from becoming rancid.

Non Food Uses of Plant Oils

Besides their dietary importance, plant oils are used to make a variety of important non food products.

Soap is made by the addition of a strong base, NaOH or NaCO3 which cleave the fatty acid chains off of the glycerol backbone. Vegetable oils are the primary source of triglycerides for soap manufacuturing.

Oils that are highly unsaturated have a strong tendency to cross link and polymerize at the double bond sites in the presence of oxygen. Such oils are used for paints and varnishes to produce a durable finish. Oilcloth is a waterproof cloth made by coating canvas with linseed (flax) oil.

Varnishes are made by combining plant oils with resins (see below), and enamels are made by combining pigmented paint with resins.

“Latex” paints are based on polymers of fatty acids derived from plant oils (mainly soybean).

The original linoleum was made by combining linseed oil from flax with ground cork. Most modern linoleum is made from petroleum but increasing demand for “green” building products is leading to the return of flax-based linoleum flooring.

Increasingly plant oils are being investigated as a substitute for petroleum for both energy and the manufacture of petroleum based products like plastics.

OIL CROP 2007 TOP COUNTRIES TOTAL WORLDMillion Metric Tonnes

Canola (rapeseed) China 10.4 49.5Canada 8.7India 7.1

Castor bean India 0.8 1.2China 0.2

Coconut Phillipines 15.6 54.7Indonesia 17.0India 9.4

Cottonseed China 22.9 72.5USA 12.0India 1.0

Linseed Canada 0.6 1.9China 0.5USA 0.1

Oil Palm Malaysia 77.7 192.5Indonesia 78.0

Olive Spain 5.8 17.5Italy 3.5Greece 2.6

Peanut China 13.1 34.9India 6.6Nigeria 3.8

Safflower India 0.2 0.5Sesame India 0.7

China 0.5Soybean USA 70.7 216.1

Brazil 58.2Argentina 45.5

Sunflower Russian Fed. 5.7 27.0Ukraine 4.2Argentina 3.5

Linseed Oil

Linseed oil is the most ancient domesticated oilseed crop

Linum usitatissimum (flax) was one of the crops domesticated in the Near East together with wheat, barley, peas, lentils ca. 8,000 BP and is also the oldest domesticated fiber crop.

Use of flax for oil predated the use of flax for fiber by several thousand years.Linseed oil is highly unsaturated and so its early uses were as a drying oil for water repellent finishes. Linseed oil was used by ancient Egyptians to coat wooden coffins.

Later linseed oil became the primary base for oil paint.

Because of its high degree of unsaturation linseed oil is prone to rancidity. It also has a strong flavor and odor, so is not commonly used any longer as a food oil. Most linseed produced now is for non food uses.

Products made from linseed include oilcloth and the original linoleum.

Scene from an Egyptian tomb depicting flax harvesting

Tung Oil

Tung oil is not an edible oil (it is poisonous), but it is highly unsaturated and so it is useful for many non food applications.

Tung oil comes from the Asian tree Aleurites fordii, a member of the Euphorbiaceae, a family that contains many species with poisonous alkaloids. Tung oil is extracted from the nuts of the tree.

Tung oil is mainly used today as a clear wood finish. It is also an ingredient in “India ink”

Safflower Oil

Safflower oil is a highly unsaturated edible oil and so has become more popular in recent years. However its popularity is declining following more recent studies that suggest highly unsaturated oils have detrimental health effects. It has the highest linoleic acid content of any seed oil. Its food uses are primarily in margarine and salad dressing.

C. tinctorius is native to the eastern Mediterranean region. The date of its domestication is unknown, but it was used as a dye around the 1st century.Because of its high unsaturation, it is grown as an oil for paint and alkyd (latex) resin.

The cake that is left over after oil pressing is high in protein (~50%) and is used as a livestock feed.

Safflower oil comes from Carthamus tinctorius an annual relative of the sunflower, and the seeds are similar.

Soybean Oil

Soybean, Glycine max, was domesticated in China around 3,000 years ago. Soybeans are the basis for many foods in China and the Orient, but most soybeans grown today are used for oil and livestock feed rather than for human food. More than 75% of the world’s production of soybeans is in North and South America and the USA is the single largest producer, around 70 million metric tonnes in 2007.

Soybean oil has a high concentration of linoleic acid (about 52%) and most soy oil is partially hydrogenated.

Soybean cake left after oil pressing is high in protein and is used as livestock feed.

The emulsifier lecithin is a by product of oil extraction. Lecithin is used in a variety of processed foods, in pharmaceuticals, margarine and in chocolate.

Soybean Oil

Increasingly soybean oil is being used as a basis for the manufacture of plastics. The potential for soy based pastics was recognized by Henry Ford in the 1940s wehn he produced a soy based plastic car.

More recently soy based plastic foams have been developed for building insulation and for upholstery cushions.

soy based foam is used in some car upholstery

Sunflower Oil

Sunflower, Helianthus annuus, is a native of North America. The related species H. tuberosum (Jerusalem artichoke) is also native to North America and is grown for its starchy root. Sunflower was domesticated by the nomadic early inhabitants of western North America 2,000 – 3,000 years ago. By the time of the European exploration of North America, sunflowers were being cultivated from Mexico to southern Canada.

Sunflower was introduced into Europe (Spain) in the 1500s but was not immediately adopted as a food crop. It eventually became a dominant oil plant in Russia.

Sunflower Oil

The seed of the sunflower is an achene (dry indehiscent fruit).

Thre is current interest in sunflower oil as a source of biodiesel fuel. Most of the sunflower crop is used for livestock feed, although some is used for cooking oil and a small amount is used for candy and snacks.

Corn OilLike the sunflower, maize (Zea mays) is a native of North America. However oil is a minor product obtained from maize. The oil content of corn is only about 2.5% by weight, but some higher oil containing varieties (~10%) have been developed. Corn oil is a byproduct of the cornmeal milling process.

Cornmeal can be produced by either a dry or wet milling process. In the wet process, the corn kernels are soaked in water and then macerated to separate the germ from the endosperm. The germs are separated from the endosperm by floatation. The liquid contains dissolved proteins and carbohydrates and the “corn steep liquor” is dried down and sold as a base for microorganism culture medium.

In the dry milling process the kernels are hydrated only slightly and the seed coat and germ are separated from the endosperm by friction. The main source of corn oil is the scutellum or single cotyledon of grasses. Oil is extracted from the separated germ with solvents instead of pressing. The starchy endosperm is used as an adjunct in beer brewing, in paper or textile manufacturing.

Most refined corn oil is used for making margarine and salad dressings. Corn oil contains natural antioxidants that help prevent spoilage, but corn oil is a poor frying oil because it smokes at cooking temperatures.

Corn oil is also high in omega-6 unsaturated fatty acids, which have been implicated in increased risk for certain types of cancer.

Sesame Oil

Sesame oil is a historically important oil, and remains a major seed oil in some countries. Sesame oil is expressed from seeds of the annual plant Sesamum indicum. The seeds are enclosed in a capsule.

Sesame is native to both Africa and India, with the center of diversity in Africa, but the earliest domestication occurred in India ca. 5000 years ago. Sesame was cultivated in the Indus valley by the Harappan culture of nw India and Pakistan ca. From there sesame spread to the eastern Mediterranean region 2000 – 4000 years ago.

While some have suggested that sesame cultivation predated the cultivation of flax for linseed oil, the oldest archeaological evidence of sesame is several thousand years younger than that of flax.

Sesame plantation in Texas

Sesame is a minor oil product in the USA but has a variety of uses. Sesame oil is high in unsaturated fats, but contains natural antioxidants sesamolin and sesamium which inhibit rancidity. Sesame oil is used in the manufacture of paints, soaps, cosmetics, perfumes and insecticides.

Sesame seeds are added as a flavoring garnish to various breads. Sweetened sesame is the basis of the Turkish confection halvah, and tahini is a paste made of sesame seeds.

Cottonseed OilCottonseed oil has become a major byproduct of the cultivation of cotton, Gossypium barbadense and G. hirsutum, as a fiber crop. So in reverse of the way that hemp and flax became used as fiber crops after their initial cultivation for seed oils, cottonseed oil has become a secondary use of cotton that developed after mechanical means for removing seeds from the cotton boll (“ginning”) were developed. Mechanical cotton gins allowed for the large scale production of cotton fiber and consequently a very large quantity of seeds.

The earliest use of cottonseed oil may have been in ancient India as a source of lamp oil. However, raw cottonseed oil contains a toxin, gossypol that makes the raw oil inedible. Most cottonseed produced before 1900 was used as fertilizer.

In 1899 David Wesson developed a purification process using steam, lye and diatomaceous earth to remove gossypol from the cottonseed oil. Wesson oil was the first modern plant based oil used for cooking. Soybean oil, canola oil, and palm oils were later added to the mix.

Cotton varieties with low amounts of gossypol are being produced by traditional plant breeding approaches and by genetic engineering.

Solidified cottonseed oil is made by hydrogenation. The first vegetable shortening, marketed as “Crisco” was made from hydrogenated cottonseed oil.

Cottonseed Oil

Cottonseed oil is high in unsaturated fats, with about 20% monounsaturated fat.It is used in a variety of processed products like mayonnaise and salad dressings and margarine and as a frying oil for deep frying foods like potato chips. Hydrogenated or partially hydrogenated cottonseed oil is used in a variety of processed food and nonfood products.

Refined cottonseed oil is favored for its neutral flavor, stability, and high polyunsaturated and monounsaturated fats.

Canola OilCanola oil comes from species of Brassica, B. napus (rapeseed) and B. campestris (turnip), relatives of cabbage, broccoli, etc.

Raw canola oil, like cottonseed oil, contains substances that give it a bitter taste. In canola, sulfur compounds (glucosinolates) and erucic acid, a bitter tasting long chain fatty acid that causes damage to heart muscle in rats in lab studies, and possibly the name “rapeseed” were obstacles to widespread use of rapeseed oil for human food. Rapeseed oil was used by Europeans several hundred years ago as a lamp oil, and it was preferred to petroleum based oils as a lubricant in steam powered machinery in the 1800s and 1900s. A demand for rapeseed oil for steamships helped drive the development of rapeseed cultivation in Canada in the first half of the 20th century.

Canadian canola

Canola Oil

Canola is an oil crop of very recent origin. Canadian plant breeders developed the first B. napus varieties low in both glucosinolates and erucic acid in the 1970s. Because of the Canadian origins this variety was named “canola”. Canola is now a generic name for B. napus varieties grown for food oils and is a registered trademark. Canola varieties must have an erucic acid content of less than 2 % and also have less than 30 micromoles of glucosinolates per gram of seed. A number of low erucic acid varieties have now been produced by both traditional and genetic engineering approaches.

About 80% of the canola grown in North America today is a genetically modified variety resistant to the herbicide Roundup, developed by the Monsanto Corp.

Canola oil is considered one of the most healthy food oils because it is low in saturated fats, intermediate in polyunsaturated fats, high in monounsaturated fats (second only to olive oil) and is also high in beneficial omega-3 fatty acids.

More recent interest in canola and other rapeseed varieties has concerned its potential as a source of biodiesel.

As with most of the other seed oils, the pressed seeds are used as a livestock feed.

Peanut Oil

Peanuts (Arachis hypogaea) are a major world crop, but a relatively small proportion of world production is used for cooking oil. Unlike other seed oils, peanut oil is not used extensively in processed foods, margarine, salad dressings etc. Its main use in cooking is as a frying oil.

Peanut oil was first produced in France in the 1860s from peanuts imported from Africa.

Peanut oil is preffered for frying because it does not smoke at high temperatures. The pressed cake is a high protein livestock feed.

Most peanuts grown in the USA are used to produce peanut butter, only about 25% of the crop is pressed for oil.

Olive Oil

Olives, Olea europea, are another of the most ancient oil crops. Olive oil differs from all the oils considered up to now in that the oil is extracted from the pulp of the olive fruit, not from the seed as for most other oil crops. Olives are also different in being a perennial tree, not an annual plant.

Archaeological evidence suggests that domestication of the olive occurred before 3500 BC (5500 years BP). However humans had undoubtedly been collecting olives from wild growing trees for several thousand years previous. The exact region of origin has not been established, but likely was the eastern Mediterranean region (Near East).

Archaeological evidence of olive cultivation comes from Crete ca 5500 years BP and Egypt ca 5100 years BP. Olives were used by both cultures for cleansing, as a skin lotion, lamp oil, foodstuff and in religious ceremonies.

Olive Oil

Olive oil is pressed from the fruits that are first macerated and the stony pits (olives are a drupe) are separated. The oil from the first cold pressing yields the “extra virgin” oil. Later pressings use heat to extract the remaining oil and are inferior to the virgin grade in having greater acidity and stronger flavors.

Olive Oil

Olive oil has the highest amount of monounsaturated fats of any plant food oil, 55 - 85% as oleic acid, as well as having several strong antioxidants. Because clinical studies suggest a relationship between monounsaturated fats and reduced cholesterol and LDL, increased HDL and reduced risk of coronary heart disease, olive oil is valued for its health benefits.

Most of the world’s production of olive oil comes from Spain, Italy and Greece.

Olive oil has a very significant place in the culture, history, religious symbolism and economy of the eastern Mediterranean region. For example the olive branch is a near universal symbol of peace, probably because in times of war,enemies attempted to destroy each others’ olive groves. Olive wreaths are a symbol of distinction and honor.