Week 7 (Unit 14)
Additionally, there are several important plant species that provide oil from the fleshy portion of the fruit:
The amount of lipids in plant tissues varies from as low as 0.1% in potatoes to about 70% in pecan nuts.
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 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.
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.
Chemical structure of fats and oils
Fatty acids are the building blocks of triglycerides (fats and oils).
Components of a fatty acid
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.
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
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
'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:
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 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.
Most seed oils are sources of 16 carbon or 18 carbon fatty acids, but there are many exceptions.
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
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.
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
There are four main stages in the extraction of oil:
Preparation of the raw material
Commercial Extraction Methods
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.
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.
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.
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
Evolution of cultivated rapeseed
Brassica napus - Rapeseed, canola; 2n = 4x = 38, AACC
Brassica oleracea - Broccoli, kale, cabbage, brussel sprouts, cauliflower, spinach
Brassica campestris - Mustard, rutabaga, turnip
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.
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.
China is the leading producer of rapeseed in the world. Canada and India are also major producers.
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.
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:
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.
Take the quiz on this Unit on the Blackboard.
British Nutrition Foundation. 2005.
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.
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.
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.
Röbbelen, G., R.K. Downey, A. Ashri. 1989. Oil crops of the world: their breeding and utilization. McGraw-Hill, New York.