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Week 7 (Unit 14)

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Oil Crops

Types of oil crops
Geographic distribution of oil crops
Oil composition and utilization
Oil processing
Oil palm
Cottonseed
Rapeseed
Sunflower
Assignments
References

Printer Friendly Version of Unit 14

Types of Oil Crops

Canola field
Photo courtesy Daryl Ehrensing, OSU

The oil of many species of plants can be used for human consumption. Oil obtained from seeds can be divided into three major categories:

  • Annual oilseeds
    • Soybean
    • Rapeseed
    • Sunflower
    • Groundnut
  • Perennial tree crops
    • Oil Palm
    • Coconut
  • By product oilseeds (derived from the germ which is removed during processing)
    • Cotton
    • Corn

Additionally, there are several important plant species that provide oil from the fleshy portion of the fruit:

  • Olive
  • Oil palm

The amount of lipids in plant tissues varies from as low as 0.1% in potatoes to about 70% in pecan nuts.

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Geographic Distribution of Oil Crops

Relative Efficiency and Ecological Distribution of Major Oil Crops

Crop Ecological habitat Oil % Oil yield Mt/ha
Oil Palm Tropical Rain Forest 20 6.0
Palm Kernel Tropical Rain Forest 50 0.8
Soybean Humid Temperate; Subtropical 20 0.7
Rapeseed Cool Temperate 45 1.8
Sunflower Temperate; Subtropical 45 1.6
Cotton Subtropical; Semi-arid Tropical 20 0.5
Peanut Humid Temperate; Tropical 48 1.4
Coconut Tropical Rainforest or Monsoon 64 2.2

 

Oil production from major food crops (averages for 2000-2002)

Crop
Oil produced (Mt)
Soya Beans 25,153,380
Palm 23,962,660
Rapeseed 12,803,750
Sunflower Seed 8,878,424
Groundnuts 5,273,495
Cotton Seed 3,915,005
Coconuts 3,473,582
Palm Kernels 2,916,384
Olive 2,570,291
Maize 1,979,614
Sesame Seed 767,940
Safflower 156,574

Source:FAOSTAT

Minor oil crops with unique characteristics

Some crops play only a minor role in world trade of oil, but are important in local markets or for production of specific products.

Meadowfoam (Limnanthes alba)

The oil from this crop has a high content of long-chain fatty acids, which give it unique physical and chemical properties. It is highly stable, biodegradable, odor free, and imparts a silky feel to cosmetics.

Oil from this crop has many potential uses:

  • Cosmetics
  • High grade industrial lubricants
  • Pharmaceuticals
  • Possible replacement for fossil fuel oils
  • Can be mixed with other vegetable oils to increase oxidative stability of those oils

Meadowfoam
Photo courtesy Daryl Ehrensing, OSU

Meadowfoam is a promising crop for the high rainfall areas of the Willamette Valley in Oregon. It has low requirements for nitrogen and fits well in a rotation with grass seed crops.


Flax (Linum usitatissimum L.)

Flax is an ancient crop, but there is increasing interest in it in recent years because it has a pleasant, nutty flavor and several nutritional benefits:

  • The oil is rich in alpha-linolenic acid, an essential, omega-3 fatty acid
  • Increasingly used as feed for chickens, to produce omega-3 enriched eggs
  • The flour is high in good-quality fiber
  • The flour is high in lignans, a type of phytoestrogen which may protect against cancer
  Flax. Photo courtesy Daryl Ehrensing, OSU

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Oil Composition and Utilization

Pure fats and oils have a common chemical structure, namely three fatty acids joined to one glycerol molecule (a triglyceride). A mixture of these triglycerides constitutes an oil or a fat. An oil will be a liquid at room temperature, whereas a fat is a solid at room temperature. Oils from different crops consist of characteristic mixtures of triglycerides and consequently have different physical and chemical properties.

Oils in human nutrition

Oils are vital components of the diet because they are an important source of energy, provide essential fatty acids, and act as carriers for the fat soluble vitamins (Vitamins A, D and E).

Fat provides our most concentrated form of energy. Its energy content (9 kcal/gram) is over twice as great as carbohydrates and proteins (4 kcal/gram).


Humans can synthesize fat from carbohydrates, so as most of us know, excess consumption of calories will end up stored as fat in our bodies. However, three essential fatty acids cannot be synthesized this way and must be incorporated in the diet. These are

  • linoleic acid
  • linolenic acid
  • arachidonic acid

Chemical structure of fats and oils

Fatty acids are the building blocks of triglycerides (fats and oils).

Components of a fatty acid

  1. A long hydrocarbon chain
    • The chain length ranges from 4 to 30 carbons; 12-24 is most common.
    • The chain is typically linear, and usually contains an even number of carbons.
  2. A carboxylic acid group


 

Fat molecules are made up of a molecule of glycerol attached to three molecules of fatty acids. The glycerol molecule has three hydroxyl groups, each able to interact with the carboxyl group of a fatty acid. Removal of a water molecule at each of the three positions forms a triglyceride. The three fatty acids in a single fat molecule may be all alike or they may be different.

glycerol
example of a triglyceride

The triglyceride shown above is typical of what is found in olive oil. It contains two radicals of oleic acid and one of palmitic acid attached to the glycerol molecule.

Classification of fatty acids

  • carbon chain length
  • number and position of double bonds (unsaturation) and functional groups (if any)

    There is a standard notation used to describe fatty acids. The oleic acid in the triglyceride shown above would be designated as 18:1, because it contains 18 carbon atoms and one double bond.

  • Saturated - No double bonds between the carbon atoms in the fatty acid chains. Most animal fats (e.g., butter) are highly saturated.
  • Monounsaturated - Have a single double bond in the fatty acid chains.
  • Polyunsaturated - Have two or more double bonds in their fatty acid chains.
  • Trans Fats - Have been partially hydrogenated producing fewer double bonds. Those that remain have been converted from a cis to a trans configuration.

Double bonds are rigid and those in natural fats introduce a kink in the molecule. This prevents the fatty acids from packing close together and as a result, unsaturated fats have a lower melting point than do saturated fats. Plant fats tend to be unsaturated ("oils"). Fats from animals tend to be saturated.

Plant oils are the most abundant (and least expensive) source of oil, but many cooking applications, particularly baked products, need solid fats. The food industry therefore uses hydrogenated oils to make shortening and margarine.

During hydrogenation, plant oils are exposed to hydrogen at a high temperature and in the presence of a catalyst. As a result

  • some double bonds are converted into single bonds
  • other double bonds are converted from the cis to trans configuration.

'Cis' and 'trans' refer to the orientation of the hydrogen atoms with respect to the double bond. 'Cis' means "on the same side" and 'trans' means "on the opposite side". The effect of converting from cis to trans is to straighten out the molecules so they can lie closer together and become solid rather than liquid.

Many studies have examined the relationship between fat in the diet and cardiovascular disease. There is still no consensus, but the evidence seems to indicate that:

  • A diet high in fat is harmful
  • Mono and polyunsaturated fats are less harmful than saturated ones, except that
  • Trans unsaturated fats may be worse than saturated fats
  • Omega-3 unsaturated fats may help to prevent cardiovascular disease.

Erucic acid (22:1) is a fatty acid that has been linked to heart disease.

Omega-3 and Omega-6 fatty acids

Omega-3 and omega-6 fatty acids are essential fatty acids that cannot be created in the human body. 'Omega' is the last letter in the Greek alphabet and designates the last carbon in the fatty acid chain. Linolenic acid is an omega-3 fatty acid because it has a double bond that is three carbons away from the omega carbon. Linoleic acid is an omega-6 fatty acid.

Some studies have suggested that omega-3 fatty acids help to protect against cardiovascular disease. For this reason, a Dietary Reference Intake (DRI) of 1.1 grams/day for women and 1.6 grams/day for men was established in September 2002.

Two other omega-3 fatty acids are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). They are not prevalent in plants but are found in human milk and fatty fish such as mackerel and salmon. In the body, arachidonic acid can be made from linoleic acid, and eicosapentaenoic and docosahexaenoic acids can be made from linolenic acid.

Free radicals

Free radicals are highly reactive forms of oxygen that are missing an electron. They are produced in very small quantities in our body as it uses fuel from food to produce energy. The effect of free radicals on human health is an active area of research. Free radical damage has been implicated as a factor in heart disease, cancer, rheumatoid arthritis, and even the process of aging. Free radicals are thought to react with phospholipids in cell membranes. Polyunsaturated fats appear to be more reactive than monounsaturated fats, and the degree of unsaturation in membrane phospholipids directly reflects the composition of fats consumed in the diet. This evidence would favor consumption of monounsaturated fats rather than polyunsaturated fats. Olive oil is an excellent source of monounsaturated fats, and canola oil is also relatively good in this regard.

What are vegetable oils?

Vegetable oils are mixtures of different triglycerides and contain other lipid-soluble compounds in addition to triglycerides.

  • triacylglycerols (triglycerides)
  • partial glycerides & free fatty acids
  • phospho- and galactolipids
  • sterols
  • pigments
  • carotenoids
  • chlorophylls

Most seed oils are sources of 16 carbon or 18 carbon fatty acids, but there are many exceptions.

Common Fatty Acids from Plants
Fatty Acid Structure Sources
Saturated (no double bonds in carbon chain)    
lauric acid 12:0 coconut oil
palmitic acid 16:0 palm oil
stearic acid 18:0 cacao bean (cocoa butter)
arachidic acid 20:0 peanut oil
monounsaturated (one double bond)    
oleic acid 18:1 olive oil
erucic acid 22:1 nonfood varieties of rapeseed
polyunsaturated (two or more double bonds)    
linoleic acid 18:2 soybean, corn, sunflower oils
linolenic acid 18:3 canola, soybean, flaxseed oils

 

 

Relative fatty acid composition of different vegetable oils

 
palmitic
stearic
oleic
linoleic
linolenic
 
erucic
 

 

16:0

18:0

18:1

18:2

18:3

20:1

22:1

22:2

Rapeseed oil
3
1
24
15
8
13
35
 
Canola oil
4
2
60
20
10
     
Cocoa butter
25
38
32
3
       
Corn oil
11
2
28
58
1
     
Cottonseed oil
22
3
19
54
1
     
Flaxseed oil
3
7
21
16
53
     
Olive oil
13
3
71
10
1
     
Palm oil
45
4
40
10
       
Peanut oil
11
2
48
32
       
Safflower oil
7
2
13
78
       
Sesame oil
9
4
41
45
       
Soybean oil
11
4
24
54
7
     
Sunflower oil
7
5
19
68
1
     
Meadowfoam oil    
2
   
61
16
18

Adapted from http://www.scientificpsychic.com/fitness/fattyacids.html

 

Adapted from the Canola Council of Canada http://www.canola-council.org/

Glucosinolates

Glucosinolates have a central (- S - C = N) group with various chains. Breakdown products from glucosinolates are toxic to animals, because they reduce palatability and iodine uptake. Rapeseed cannot be used for animal feed due to the presence of erucic acid and glucosinolates.

Uses of seed oils

Edible products

  • salad oil
  • margarine
  • shortenings
  • cooking oil
  • baking and confection
  • canning industry
  • animal feeds

Industrial products

  • pharmaceuticals
  • soaps and detergents
  • paints, coatings, and resins
  • linoleum
  • cosmetics
  • lubricants
  • plastics
  • waxes and candles
  • fuels

Vegetable oils have great potential as clean, renewable biofuels that can reduce our dependency on fossil fuels. For further information on this topic, visit the Alternative Fuels Data Center. The EPA has also published a factsheet on Biodiesel.

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Oil Processing

Source: http://www.processingtalk.com/news/met/met126.html

Lipids are water insoluble organic compounds that are soluble in an organic solvent (hexane, ether, etc.). Fats, oils, waxes, and steroids are lipids.

Objectives of oilseed processing

  1. Maximize oil yield
  2. Minimize damage to oil and meal
  3. Minimize impurities
  4. Maximize value of meal

There are four main stages in the extraction of oil:

  1. preparation of the raw material
  2. extraction
  3. clarification
  4. packaging and storage

Preparation of the raw material

  • Decortication - removal of the fibrous husk or seed coat
  • Winnowing - separating the husks or seed coats from the oil-bearing material
  • Cracking
  • Pulping/grinding/flaking/grating
  • Heating/conditioning - for some crops, heating with water helps to rupture the oil-bearing cells and also decreases the thickness of the oil, allowing it to flow more easily

 

Oil Expeller. Photo courtesy Daryl Ehrensing, OSU

Extraction

Commercial Extraction Methods

  • Expeller Pressing - Oil is mechanically squeezed from the seeds
    • Oil presses- a plunger pushes against the raw materials and squeezes the oil out through perforations in the container.
    • Oil expellers - Expellers use a rotating screw which feeds raw material into a casing with perforated walls. Oil passes out through the perforations and the oil cake (residue) is pushed out of the end of the expeller.
  • Prepress / Solvent Extraction - Part pressing, part solvent
  • Direct Solvent Extraction - Oil is removed by an organic solvent; afterwards, the solids must be separated and the solvent must be recovered.
  • Mechanical pressing produces an oilcake whereas solvent extraction produces seed meal.

Clarification (refining)

  • Degumming
  • Bleaching
  • Deodorizing
  • Winterizing

Impurities are removed by allowing the oil to stand for several days and settle out. Water may also be added and then removed with heat to kill bacteria. This step can extend the shelf-life of the oil considerably.

Oilseeds produce seed meals or oilcakes in addition to the oil.

 

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Oil Palm

Oil palm typically yields 5-7 t/ha of oil, which is far more than any other oil crop.

There are two important cultivated species of oil palm:

  • Elaeis guineensis Jacq. - African oil palm
  • Elaeis oleifera - American oil palm

These species can be readily intermated, despite their different origins. Although E. guineensis is by far the most widely grown species, E. oleifera is valued in breeding programs for its slow vertical growth rate and resistance to diseases, particularly heart rot.

Palm trees are long-lived. They generally become productive after about two years of growth and are exploited for 25-30 years. Palm trees can remain productive for 140 years or more. Fruit can be harvested throughout the year.

Photo courtesy Daryl Ehrensing, OSU


Oil palm is monoecious, but male and female flowers are borne at different times on the same tree, so the crop is entirely allogamous (outcrossing). Pollination is carried out by insects.

At maturity, the fruit is a reddish-orange drupe which consists of the pulp, the shell, and the kernel. Varieties may be thick-shelled, thin-shelled or shell-less. A single gene controls the thin-shelled characteristic, which may impart a 25% yield advantage over thick-shelled types.

Most of the oil is obtained from the fleshy fruit (mesocarp), but palm kernels are also an important source of oil.


Photo courtesy Daryl Ehrensing, OSU

Oil palm is grown in the humid tropics extending from 15 °N to 15 °S of the Equator. Highest yields are obtained with about 2000 mm annual rainfall. Major regions for oil palm production include South-East Asia (Malaysia and Indonesia), West and Central Africa, and South America.

Leading producers of Oil Palm based on averages for 2000-2002

Country

Area Harv (Ha)

Production (Mt)

Malaysia
3,251,667 60,983,330
Indonesia 2,204,667 38,226,670
Nigeria 3,146,667 8,406,667
Thailand 221,867 3,748,333
Colombia 139,424 2,573,333
Côte d'Ivoire 140,333 1,523,667
Ecuador
114,333 1,316,667
Papua New Guinea 75,667 1,210,000
Cameroon 56,025 1,050,000
Ghana 115,000 1,050,000
Congo, Democratic Republic 210,000 946,667
Guinea 310,000 830,000

End-use quality

In comparison to other vegetable oils, palm oil is relatively high in saturated fats (about 50%, mostly palmitic acid). The predominant unsaturated fatty acids are oleic and linoleic acids.

Oil from the kernel is even higher in saturation, with qualities similar to coconut oil. It is a liquid in tropical climates and a solid in temperate areas.

Oil palm differs from most oil seed crops, because it must be processed locally before it can be transported.

Unbleached palm oil is generally red in color and is an important source of Vitamin A in some tropical areas.

Palm wine can be made from the sap obtained by tapping the male inflorescence. The sap is high in sugars and ferments quickly. It is also an important source of B Vitamins in the diets of people of West Africa.

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Cottonseed

Source: http://www.hort.purdue.edu/newcrop/Crops/Cotton_seed_oil.html

Cotton is grown primarily for the seed fibers, and cottonseed is a secondary product.

Of the thirty-nine species in the genus Gossypium, four are cultivated:

  • Diploid species
    • G. arboreum L.
    • G. herbaceum L.
  • Tetraploid species
    • G. barbadense L.
    • G. hirsutum L.
  Photo courtesy Daryl Ehrensing, OSU

Major cotton producing countries include China, the USA, India, Uzbekistan, Pakistan, Turkey, Brazil, and all francophone countries in West and Central Africa. The plant's requirement for high temperatures restricts its adaptation to tropical and subtropical climates, but cultivars have been developed that can be grown in temperate areas that have at least a 180-day frost-free cropping season.

The cultivated cottons are perennials, but they are cultivated as annuals. The fruits are capsules (bolls) which dehisce (burst open) as they ripen. Each capsule contains up to 40 or 50 seeds, to which the fibers or lint are attached. In the US, cotton lint is removed from the bolls in cotton gins. The seeds are cleaned further to remove the lint and then pressed or put through expellers. A high quality oil is obtained. The cotton meal or press cake is a valuable high-protein livestock feed.

Primary uses of cottonseed oil

  • shortenings
  • cooking and salad oils
  • margarines
  • soap manufacture

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Rapeseed and Canola

Canola is a name used for edible oilseed rape. It is a member of the mustard family (Cruciferae). All current varieties of rapeseed were developed from:

Brassica napus - winter rape, Argentine rape
Brassica campestris - springrape, Polish rape

Canola varieties are "double low" which means that the processed oil contains less than 2% erucic acid and the meal has less than 3 mg/g of glucosinolates.

Canola seed is high in oil content (40%), protein (23%) and polyunsaturated fatty acids (oleic, linoleic, and linolenic).

  Photo courtesy Daryl Ehrensing, OSU

Evolution of cultivated rapeseed

Brassica napus - Rapeseed, canola; 2n = 4x = 38, AACC

Amphiploid (having two sets of chromosomes, each coming from a different ancestor) of B. campestris and B. oleracea

Brassica oleracea - Broccoli, kale, cabbage, brussel sprouts, cauliflower, spinach

2n=18, CC

Brassica campestris - Mustard, rutabaga, turnip

2n=20, AA

B. napus crosses readily with B. campestris. Crosses with B. oleracea are extremely difficult to achieve.

Growth and adaptation

Canola is a cool season crop that requires adequate moisture and cool night temperatures to recover from extreme heat or dry weather.

Winter and spring types are available. Winter types are grown mostly in Europe, China, and the eastern U.S. They require three weeks of near-freezing temperatures to become fully vernalized and to start rapid vegetative growth. Spring types are grown in Canada, northern Europe, and China. Canola is cold tolerant, but the level of tolerance depends on the extent of pre-hardening and developmental stage of the plant. Hardened spring types can survive temperatures of –10 °C, and hardened winter types can survive short periods with temperatures as low as –20 °C.

Canola is very sensitive to high temperatures, particularly at flowering time. Prolonged heat stress during seed maturation can reduce oil content and seed quality.

Rapeseed prefers light, sandy soils with good drainage. It will not tolerate heavy, wet soils.

Rapeseed utilizes 25-30% more nitrogen than cereal crops such as wheat. Most of the nitrogen is taken up before bolting. It also has relatively high requirements for boron and sulfur.

This is a small-seeded crop, so seedling growth is not vigorous. For good stand establishment, the seedbed must be firm and seeding depth must be uniform and shallow.

A well-established rapeseed crop will compete well with weeds.

Photo courtesy Daryl Ehrensing, OSU

Rapeseed is primarily self-pollinated (80%+) and tolerant of inbreeding. The inflorescence is a raceme, and flowering occurs over a period of 14 to 21 days. Pods are filled completely in 35 to 45 days after flowering is initiated. Seeds are borne in long, slender pods. Harvesting must be done on time to avoid losses due to seed shattering.

 

Photo courtesy Daryl Ehrensing, OSU

Diseases and Pests

White mold (stem rot caused by Sclerotinia sclerotiorum) can be serious in cool, moist growing conditions. Symptoms are sudden wilting and premature plant death.

The greatest insect problem is the flea beetle, which attacks seedlings at emergence. Effective insecticides are available.

Production statistics

China is the leading producer of rapeseed in the world. Canada and India are also major producers.

Leading producers of rapeseed based on averages for 2000-2002

Country

Area Harv (Ha)

Production (Mt)

China 7,196,392 11,080,690
Canada 3,928,933 5,236,234
India 5,181,300 5,005,334
Germany 1,170,873 3,864,253
France 1,101,418 3,186,606
Australia 1,336,333 1,384,333
UK 428,333 1,250,333
Poland 438,786 1,005,525
Czech Rep 326,624 842,427
USA 571,703 841,213
Source: FAOSTAT


Most of the canola grown in the world is produced in Canada.

 

  Map of Canola production in Canada
Courtesy the Canola Council of Canada

 

Quality and utilization

Production and utilization of rapeseed increased with the development of steam power, when it was found that rapeseed oil would cling to wet metal surfaces better than other lubricants.

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Sunflower

Sunflower (Helianthus annus L.) grows well in temperate climates throughout the world. It is grown primarily for oil, but certain cultivars are utilized for their edible seeds, particularly in the USA. Sunflower meal is high in protein and is used in food rations for livestock and poultry. Sunflower oil is considered to be of high quality for salad dressing and cooking.

Sunflower heads will turn with the sun up until anthesis; thereafter the heads will face the east.

Sunflower belongs to the Asteraceae family. There are about 67 species in the genus Helianthus, and they are all native to the Americas. The genus includes annuals, perennials, and shrub species.


Photo courtesy Daryl Ehrensing, OSU

A sunflower plant has one conspicuous head and a single stem. The head consists of an outer whorl of ray flowers ("petals") which are generally sterile, and the inner disk flowers which are perfect and produce the seeds. Sunflower is highly cross-pollinating, primarily by insects. With some cultivars, yields will be improved by the use of bee pollinators. A single plant can produce up to 3,000 seeds.

Hybrids can be produced using a cytoplasmic male sterility and fertility restorer system.

Major diseases of sunflower in the USA and Canada include:

  • Rust (Puccinia helianthi)
  • Downy mildew (Plasmopara halstedi)
  • Verticillium wilt (Verticillium dahliae)
  • Sclerotinia stalk and head rot (Sclerotinia sclerotiorum)
  • Phoma black stem (Phoma macdonaldii)

Sunflowers are susceptible to a number of insect pests and bird damage. See the Alternative Field Crops website on Sunflower for more information.

Sunflower grows well in temperate climates throughout the world. About 85% of the crop in the US is produced in North and South Dakota and Minnesota.

Leading producers of sunflower seed, based on averages for 2000-2002 (FAOSTAT)

Country Area Harv (Ha) Production (Mt)
Argentina 2,465,320 4,364,092
Russian Federation
3,880,767 3,400,000
Ukraine 2,651,867 2,992,800
China 1,128,307 1,777,330
France 686,191 1,645,468
USA 999,177 1,430,393
Romania 830,640 845,483
Spain 817,700 825,433
Turkey 530,667 750,000
India 1,176,767 747,333
South Africa 521,185 710,392
Hungary 345,605 631,638
Bulgaria 461,014 508,980

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Assignments

Quiz

Take the quiz on this Unit on the Blackboard.

References

British Nutrition Foundation. 2005.
http://www.nutrition.org.uk

Canola Council of Canada. http://www.canola-council.org/

Hartley, C.W.S. 1988. The oil palm. Longman Scientific & Technical, UK.

Jaquemand, J-C., L. Baudouin, and J-M Noiret. Oil Palm. In A. Charrier, M. Jacquot, S. Hamon, and D. Nicolas (eds.) Tropical Plant Breeding. CIRAD, France.

Meadowfoam Seed Oil website. http://www.meadowfoam.com

Oelke, E.A., E.S. Oplinger, C.V. Hanson, K.A. Kelling. 1990. Meadowfoam. Alternative Field Crops Manual. University of Wisconsin Cooperative Exension and the University of Minnesota Extension Service.
http://www.hort.purdue.edu/newcrop/afcm/meadowfoam.html

Oplinger, E.S., L.L. Hardman, E.T. Gritton, J.D. Doll, and K.A. Kelling. 1989. Canola. Alternative Field Crops Manual. University of Wisconsin Cooperative Exension and the University of Minnesota Extension Service.
http://www.hort.purdue.edu/newcrop/afcm/canola.html

Putnam, D.H., E.S. Oplinger, D.R. Hicks, B.R. Durgan, D.M. Noetzel, R.A. Meronuck, J.D. Doll, and E.E. Schulte. 1990. Sunflower. Alternative Field Crops Manual. University of Wisconsin Cooperative Exension and the University of Minnesota Extension Service.
http://www.hort.purdue.edu/newcrop/afcm/sunflower.html

Röbbelen, G., R.K. Downey, A. Ashri. 1989. Oil crops of the world: their breeding and utilization. McGraw-Hill, New York.

 

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