|
VEGETABLE FATS AND OILS
Vegetable fats and oils are organic compounds not miscible with water, derived from plants. Nominally, oils are liquid at ambient temperature, and fats are solid, but this is an imprecise definition, as ambient temperatures vary, and typically there are "melting ranges" rather than "melting points". A dense brittle fat is a wax.
Vegetable fats and oils include several categories of compounds: essential oils, macerated oils, and triglycerides. Hydrogenated oils are a chemically-modified triglyceride. Macerated oils are a deliberately-adulterated oil, typically using a triglyceride as the base.
Essential oils
An essential oil is a concentrated, hydrophobic liquid containing volatile aromatic compounds extracted from plants. It may be produced by distillation, expression, or solvent extraction. Essential oils are used in perfumery, aromatherapy, cosmetics, incense, for flavoring food and drink, and to a lesser extent, in medicine and household cleaning products. They are valuable commodities to the fragrance and flavorant industries.
Essential oil is also known as volatile oil and ethereal oil. It may also be referred to as "oil of" the raw plant material from which it was extracted, such as oil of clove. The term essential is intended to indicate that the oil is the fragrant essence of the plant from which it is extracted and not in the more common sense of being indispensable. It is not to be confused with essential fatty acids.
Medical use of vegetable oils has a long and distinguished history. Many oils that are use medicinally are essential oils, which are distilled rather than pressed or otherwise extracted. Medical properties claimed by those who sell medicinal oils vary from skin treatments to remedies for cancer, and are often based on historical use of these oils for these purposes. Such claims are now subject to regulation in most countries, and have grown correspondingly more vague, to stay within these regulations.
Interest in such uses of essential oils has enjoyed a revival in recent decades, with the popularity of aromatherapy, in which oils are heated and volatilized.
Production
-
Distillation
Today, most common essential oils, such as lavender, peppermint, and eucalyptus, are distilled. Raw plant material, consisting of the flowers, leaves, wood, bark, roots, seeds, or peel, is put into an alembic (distillation apparatus) over water, As the water is heated the steam passes through the plant material, vaporizing the volatile compounds. The vapors flow through a coil where they condense back to liquid, which is then collected in a holding vessel.
Most oils are distilled in a single process. One exception is Ylang-ylang (Cananga odorata), which takes 22 hours to complete through a Fractional distillation.
The water recondensed from the distillation process is referred to as a hydrosol, hydrolat, or plant water essence, which may be sold as another fragrant product. Popular hydrosols are rose water, lavender water, and orange blossom water. Many plant hydrosols have unpleasant smells and are therefore not sold.
Expression
Most citrus peel oils are usually expressed mechanically, or cold-pressed. Due to the large quantities of oil in citrus peel and the relatively low cost to grow and harvest the raw materials, citrus-fruit oils are cheaper than most other essential oils. Lemon or sweet orange oils that are obtained as by-products of the commercial citrus industry are even cheaper.
Prior to the discovery of distillation, essential oils (EO) were extracted by pressing.
Solvent extraction
Most flowers contain very little volatile oil to undergo expression and their chemical components are too delicate and easily denatured by the high heat used in steam distillation. Instead, a solvent such as hexane or supercritical carbon dioxide is used to extract the oils. Extracts from hexane and other hydrophobic solvent are called concretes, which is mixture of essential oil, waxes, resins, and other lipophilic (oil soluble) plant material.
Although highly fragrant, concretes contain large quantities of non-fragrant waxes and resins. As such another solvent, often ethyl alcohol, which only dissolves the fragrant low-molecular weight compounds is used to extract the fragrant oil from the concrete. The alcohol is removed by a second distillation, leaving behind the absolute.
In supercritical fluid extraction, liquid carbon dioxide is used as a solvent. This method has many benefits, including avoiding petrochemical residues in the product, obtaing absolute directly without having to deal with a concrete, and a lower temperature process to prevents the decomposition and denaturing of compounds. This process is identical to one of the techniques for making decaffeinated coffee.
Production quantities
Main high-volume products - turpentine; orange and lemon (see orange oil), mint and citronella are essential oils. In ~2000, tonnes:
Essential oil use in aromatherapy
-
Aromatherapy is a form of herbal medicine, in which healing effects are ascribed to the aromatic compounds in essential oils and other plant extracts. Many common essential oils have medicinal properties that have been applied in folk medicine since ancient times and are still widely used today. For example, many essential oils have antiseptic properties, though some are stronger than others. In addition, many have an uplifting effect on the mind, though different essential oils have different properties.
Solvents
Essential oils are lipophilic compounds so it has been found that alcohols such as methanol and ethanol( primarily 100% Concentrations) or organic solvents such as acetone are the best diluents to be used for dilution. Water is not recommended as water and fats do not dissolve in one another, although oil dilution in water can be achieved at extremely low concentrations of oil, also depending on the viscosity of the oil.
Raw materials
-
Essential oils are derived from various parts of plants. Some, like orange oil, are derived from any of several parts of the plant.
-
Rose oil
-
The most well-known essential oil is probably Rose oil, produced from Rosa damascena and Rosa centifolia. Steam-distilled rose oil is know as "rose otto or "attar of roses" while oil which is solvent-extracted is know as "rose absolute".
Dangers
The smoke from burning essential oils may contain potential carcinogens, such as polycyclic aromatic hydrocarbons (PAHs). Essential oils are naturally high in volatile organic compounds (VOCs). The internal use of essential oils should be fully avoided during pregnancy without consulting with a licensed professional, as some can be abortifacients in dose 0.5–10 ml.
Toxical data: LD50 of most EO or their main components are 0.5-10 g/kg (orally or skin test).
Because of their concentrated nature, EO's generally should not be applied directly to the skin in their undiluted or "neat" form. Some can cause severe irritation or provoke an allergic reaction. Instead, essential oil should be applied with a plants oils or other fats (carrier oil), such as olive, hazelnut, or any other "soft" oil. Common ratio of essential oil disbursed in a carrier oil is 0.5–3% (most less than 10%) and depends on its purpose. Some EO's including many of the citrus peel oils, are photosensitizers, increasing the skin's reaction to sunlight and making it more likely to burn.
Industrial users of essential oils should consult the material safety data sheets (MSDS) to determine the hazards and handling requirements of particular oils.
There is some concern about pesticide residues in EO's, particularly those used therapeutically. For this reason, many practitioners of aromatherapy choose to buy organically produced oils.
While some advocate the ingestion of essential oils for therapeutic purposes, this should never be done except under the supervision of a professional who is licensed to prescribe such treatment. Some very common EO's such as Eucalyptus are extremely toxic internally. Pharmacopoeia standards for medicinal oils should be heeded. EO's should always be kept out of the reach of children. Some oils can be toxic to some domestic animals, cats in particular. Owners must ensure that their pets do not come into contact with potentially harmful essential oils. [1]
Macerated oils
Macerated oils are vegetable oils to which other matter has been added, such as herbs. Commercially-available macerated oils include all these, and others. Herbalists and aromatherapists use not only these pure macerated oils, but blends of these oils, as well, and may macerate virtually any known herb. Base oils commonly used for maceration include almond oil, sunflower oil, and olive oil as well as other food-grade triglyceride vegetable oils, but other oils undoubtedly are used as well.
Triglyceride vegetable fats and oils
Triglyceride vegetable fats and oils include not only edible fats and oils from vegetable sources, but inedible vegetable waxes and oils such as linseed oil, tung oil, jojoba oil and castor oil, used in lubricants, paints, cosmetics, pharmaceuticals, and other industrial purposes. Although thought of as esters of glycerin and a varying blend of fatty acids, in fact these oils contain free fatty acids and diglycerides as well.
Triglyceride-based vegetable fats and oils can be transformed through partial or complete hydrogenation to fats and oils of greater molecular weight. The hydrogenation process involves sparging the oil at high temperature and pressure with hydrogen in the presence of a catalyst, typically a powdered nickel compound. As each double-bond in the triglyceride is broken, two hydrogen atoms form single bonds. The elimination of double-bonds by adding hydrogen atoms is called saturation; as the degree of saturation increases, the oil progresses towards being fully hydrogenated. Oils may be hydrogenated to increase resistance to rancidity (oxidation) or to change the physical characteristics. As the degree of saturation increases, the oil becomes more viscous, and temperature at which it liquifies increases.
The use of hydrogenated oils in foods has never been completely satisfactory. Because the center arm of the triglyceride is shielded somewhat by the end triglycerides, most of the hydrogenation occurs on the end triglycerides. This makes the resulting fat more brittle. A margarine made from tropical oils, which are naturally more saturated, will be more plastic (more "spreadable") than a margarine made from hydrogenated soy oil. (In the U.S., the USDA Standard of Identity for a product labeled as vegetable oil margarine specifies that only canola, safflower, sunflower, corn, soybean, or peanut oil may be used.[2] Products not labeled vegetable oil margarine do not have that restriction.) In addition, hydrogenation results in the formation of trans fats, which have increasingly been viewed as unhealthful since the 1970s. For non-food purposes, however, such as vegetable replacements for lanolin, degras or spermaceti, or the production of soap, hydrogenation appears to present no particular health risks.
Although in principle other parts of plants may yield oil, in practice seeds from oilseed plants form the almost exclusive source.
Like all fats, these vegetable oils are , and are insoluble in water but soluble in organic solvents.
Uses of triglyceride vegetable oil
Oils extracted from plants have been used in many cultures, since ancient time. As an example, in a 4,000 year old "kitchen" unearthed in Indiana's Charlestown State Park, archaeologist Bob McCullough of IPFW found evidence that natives used large slabs of rock to crush hickory nuts, then boiled them in water to extract the oil. [3]
Culinary uses
-
Many vegetable oils are consumed directly, or used directly as ingredients in food - a role that they share with some animal fats, including butter and ghee. The oils serve a number of purposes in this role:
- Texture - oils can serve to make other ingredients stick together less.
- Flavor - while less-flavorful oils command premium prices, oils such as olive oil or almond oil may be chosen specifically for the flavor they impart.
- Flavor base - oils can also "carry" the flavors of other ingredients, since many flavors are present in chemicals that are soluble in oil.
Secondly, oils can be heated, and used to cook other foods. Oils that are suitable for this purpose must have a high flash point. Such oils include the major cooking oils - canola, sunflower oil, safflower oil, peanut oil, etc. Some oils, including rice bran oil, are particularly valued in Asian cultures for high temperature cooking, because of their unusually high flash point.
Industrial uses
Many vegetable oils are used to make soaps, skin products, perfumes and other personal care and cosmetic products.
Some oils are particularly suitable as drying agents, and are used in making paints and other wood treatment products. Dammar oil, for example, is used almost exclusively in treating the hulls of wooden boats.
Vegetable oils are increasingly being used in the electrical industry as insulators as vegetable oils are non-toxic to the environment, biodegradable if spilled and have high flash and fire points. However, vegetable oils have issues with chemical stability (there has to be a tradeoff with biodegradability), so they are generally used in systems where they are not exposed to oxygen and are more expensive than crude oil distillate. Three examples are Midel 7131 by M & I materials, FR3 by Cooper Power and Biotemp by ABB. Midel 7131 is a synthetic oil, manufactured by an alcohol + acid reaction.
Common vegetable oil has also been used experimentally as a cooling agent in PCs.
One limiting factor in industrial uses of vegetable oils is that all such oils eventually decompose, chemically, turning rancid. Oils that are more stable (e.g. Ben oil) are therefore particularly valued for industrial application.
Fuel
-
Vegetable oils are also the basis of biodiesel, which can be used like conventional diesel, and SVO (straight vegetable oil), which can be used in specially prepared vehicle engines.
Extraction
The "modern" way of processing vegetable oil is by chemical extraction, using solvent extracts, which produces higher yields and is quicker and less expensive. The most common solvent is petroleum-derived hexane. This technique is used for most of the "newer" industrial oils such as soybean and corn oils.
Another way is "physical extraction," which does not use solvent extracts. It is made the "traditional" way using several different types of mechanical extraction. This method is typically used to produce the more traditional oils (e.g., olive), and it is preferred by most "health-food" customers in the USA and in Europe. Expeller-pressed extraction is one type, and there are two other types that are both oil presses: the screw press and the ram press. Oil seed presses are commonly used in developing countries, among people for whom other extraction methods would be prohibitively expensive. [4]
Supercritical carbon dioxide can also be used for the extraction purpose and is non toxic.[5]
Production
Crude oil, straight from the crushing operation, is not considered edible in the case of most oilseeds. The same is true for the remaining meal. For instance, animals fed raw soy meal will waste away, even though soy meal is high in protein. Researchers at Central Soya discovered that a trypsin inhibitor in soybeans could be deactivated by toasting the meal, and both licensed their invention, and sold soy meal augmented with vitamins and minerals as MasterMix, a product for farmers to mix with their own grain to produce a high quality feed.
The processing of soy oil is typical of that used with most vegetable oils. Crude soy oil is first mixed with caustic soda. Saponification turns free fatty acids into soap. The soap is removed with a centrifuge. Neutralized dry soap stock (NDSS) is typically used in animal feed, more to get rid of it than because it is particularly nourishing. The remaining oil is deodorized by heating under a near-perfect vacuum and sparged with water. The condensate is further processed to become vitamin E food supplement, while the oil can be sold to manufacturers and consumers at this point.
Some of the oil is further processed. By carefully filtering the oil at near-freezing temperatures, "winter oil" is produced. This oil is sold to manufacturers of salad dressings, so that the dressings do not turn cloudy when refrigerated.
The oil may be partially hydrogenated to produce various ingredient oils. Lightly hydrogenated oils have very similar physical characteristics to regular soy oil, but are more resistant to becoming rancid.
Margarine oils need to be mostly solid at 32 °C (90 °F) so that the margarine does not melt in warm rooms, yet it needs to be completely liquid at 37 °C (98 °F), so that it doesn't leave a "lardy" taste in the mouth.
Another major use of soy oil is for fry oils. These oils require substantial hydrogenation to keep the polyunsaturates of soy oil from becoming rancid.
Hardening vegetable oil is done by raising a blend of vegetable oil and a catalyst in near-vacuum to very high temperatures, and introducing hydrogen. This causes the carbon atoms of the oil to break double-bonds with other carbons, each carbon forming a new single-bond with a hydrogen atom. Adding these hydrogen atoms to the oil makes it more solid, raises the smoke point, and makes the oil more stable.
Hydrogenated vegetable oils differ in two major ways from other oils which are equally saturated. During hydrogenation, it is easier for hydrogen to come into contact with the fatty acids on the end of the triglyceride, and less easy for them to come into contact with the center fatty acid. This makes the resulting fat more brittle than a tropical oil; soy margarines are less "spreadable". The other difference is that trans fatty acids (often called trans fat) are formed in the hydrogenation reactor, and may amount to as much as 40 percent by weight of a partially hydrogenated oil. Trans acids are increasingly thought to be unhealthy.
Particular oils
-
The following triglyceride vegetable oils account for almost all world-wide production, by volume. All are used as both cooking oils and as SVO or to make biodiesel. According to the USDA, the total world consumption of major vegetable oils in 2000 was:
| Oil source |
World consumption
(million tons) |
Notes |
| Soybeans |
26.0 |
Accounts for about half of worldwide edible oil production. |
| Palm |
23.3 |
The most widely produced tropical oil. Also used to make biofuel. |
| Rapeseed |
13.1 |
One of the most widely used cooking oils, Canola is a (trademarked) variety (cultivar) of rapeseed. |
| Sunflowerseed |
8.6 |
A common cooking oil, also used to make biodiesel. |
| Peanut |
4.2 |
Mild-flavored cooking oil. |
| Cottonseed |
3.6 |
A major food oil, often used in industrial food processing. |
| Palm Kernel |
2.7 |
From the seed of the African palm tree |
| Olive |
2.5 |
Used in cooking, cosmetics, soaps and as a fuel for traditional oil lamps |
Note that these figures include industrial and animal feed use. The majority of European rapeseed oil production is used to produce biodiesel, or used directly as fuel in diesel cars which may require modification to heat the oil to reduce its higher viscosity. The suitability of the fuel should come as little surprise, as Rudolph Diesel originally designed his engine to run on peanut oil.
Other significant triglyceride oils include:
History of edible vegetable oils in the United States
While olive oil and other pressed oils have been around for millennia, Procter & Gamble researchers were innovators when they started selling cottonseed oil as a creamed shortening, in 1911. Ginning mills were happy to have someone haul away the cotton seeds. P&G researchers learned how to extract the oil, refine it, partially hydrogenate it (causing it to be solid at room temperature and thus mimic natural lard), and can it under nitrogen gas. Compared to the rendered lard P&G was already selling to consumers, Crisco was cheaper, easier to stir into a recipe, and could be stored at room temperature for two years without turning rancid. (P&G sold their fats and oils brands - Jif and Crisco - to The J.M. Smucker Co. in 2002.)
Soybeans were an exciting new crop from China in the 1930s. Soy was protein-rich, and the light tasteless oil was extremely high in polyunsaturates. Henry Ford established a soybean research laboratory, developed soybean plastics and a soy-based synthetic wool, and built a car almost entirely out of soybeans. Roger Drackett had a successful new product with Windex, but he invested heavily in soybean research, seeing it as a smart investment. By the 1950s and 1960s, soybean oil had became the most popular vegetable oil in the US.
In the mid-1970s, Canadian researchers developed a low-ecruic rapeseed cultivar. Because the word "rape" was not considered optimal for marketing, they coined the name "canola" (from "Canada Oil"). The FDA approved use of the canola name in January 1985,[6] and U.S. farmers started planting large acreages that spring. Canola oil is lower in saturated fats, and higher in mono-unsaturates and is a better source of omega-3 fats than other popular oils. Canola is very thin (unlike corn oil) and flavorless (unlike olive oil) so it largely succeeds by displacing soy oil, just as soy oil largely succeeded by displacing cottonseed oil.
Waste oil
As of 2000, the United States were producing in excess of 11 billion liters of waste vegetable oil annually, mainly from industrial deep fryers in potato processing plants, snack food factories and fast food restaurants.
Waste vegetable oil, sold as the commodity yellow grease has a market value of approximately $1.09 per US gallon ($0.29/l or $335 per metric tonne), expected to rise to $1.21 by 2013, enough to make collection economically viable.[7]
Currently, the largest uses of waste vegetable oil in the U.S. are for animal feed, pet food, and cosmetics. Since 2002, an increasing number of European Union countries have prohibited the inclusion of waste vegetable oil from catering in animal feed. Waste cooking oils from food manufacturing, however, as well as fresh or unused cooking oil, continues to be used in animal feed. [8]
See also
References
- ^ Arnica Oil. Vitality Works. Retrieved on 2006-08-11.
- ^ USDA Standard of Identity
- ^ 4,000-year-old 'kitchen' unearthed in Indiana. Retrieved on 2006-07-31.
- ^ Janet Bachmann. Oilseed Processing for Small-Scale Producers. Retrieved on 2006-07-31.
- ^ M. Eisenmenger, N. Dunford, F. Eller and S. Taylor (2005). "Pilot Scale Supercritical Carbon Dioxide Extraction and Characterization of Wheat Germ Oil". AOCS Proceedings 96.
- ^ Canola oil. Retrieved on 2006-07-31.
- ^ Anthony Radich. Biodiesel Performance, Costs, and Use (PDF). Retrieved on 2006-07-31.
- ^ Waste cooking oil from catering premises. Retrieved on 2006-07-31.
Other references
- Schnaubelt, Kurt. Advanced Aromatherapy: The Science of Essential Oil Therapy. Healing Arts Press, 1999. ISBN 0-89281-743-7
- Sellar, Wanda. The Directory of Essential Oils Essex: The C.W.Daniel Company, Ltd. Reprint, 2001. ISBN 0-85207-346-1
- Tisserand, Robert. Essential Oil Safety: A Guide for Health Care Professionals. Churchill Livingstone, 1995. ISBN 0-443-05260-3
- Beare-Rogers, J.L. 1983. "Trans and positional isomers of common fatty acids." In H.H. Draper (ed.) Advances in Nutritional Research. Vol. 5 Plenum Press, New York, pp. 171-200.
- Berry, E.M. and Hirsch, J. 1986. "Does dietary linolenic acid influence blood pressure?" American Journal of Clinical Nutrition. 44: 336-340.
- Beyers, E.C. and Emken, E.A. 1991. "Metabolites of cis, trans, and trans, cis isomers of linoleic acid in mice and incorporation into tissue lipids." Biochimica et Biophysica Acta. 1082: 275-284.
- Birch, D.G., Birch, E.E., Hoffman, D.R., and Uauy, R.D. 1992. "Retinal development in very-low-birth-weight infants fed diets differing in omega-3 fatty acids." Investigative Ophthalmology and Visual Science 33(8): 2365-2376.
- Birch, E.E., Birch, D.G., Hoffman, D.R., and Uauy, R. 1992. "Dietary essential fatty acid supply and visual acuity development." Investigative Ophthalmology and Visual Science. 33(11): 3242-3253.
- Brenner, R.R. 1989. Factors influencing fatty acid chain elongation and desaturation, in the role of fats in human nutrition. 2nd edn. (eds A.J. Vergroesen and M. Crawford), Academic Press, London pp. 45-79.
- British Nutrition Foundation. 1987. Report of the task force on trans fatty acids. London: British Nutrition Foundation.
- Central Soya annual report, 1979.
- Emken, E. A. 1984. "Nutrition and biochemistry of trans and positional fatty acid isomers in hydrogenated oils." Annual Reviews of Nutrition. 4: 339-376.
- Enig, M.G., Atal, S., Keeney, M and Sampugna, J. 1990. "Isomeric trans fatty acids in the U.S. diet." Journal of the American College of Nutrition. 9: 471-486.
- Ascherio, A., Hennekens, C.H., Baring, J.E., Master, C., Stampfer, M.J. and Willett, W.C. 1994. "Trans fatty acids intake and risk of myocardial infarction." Circulation. 89: 94-101.
- Gurr, M.I. 1983. "Trans fatty acids: Metabolic and nutritional significance." Bulletin of the International Dairy Federation. Document 166: 5-18.
- Hui Y. H., editor, "Bailey's Industrial Oil and Fat Products," Edible Oil and Fat Products
- Koletzko, B. 1992. "Trans fatty acids may impair biosynthesis of long-chain polyunsaturates and growth in man." Acta Paediatrica. 81: 302-306.
- Lief, Alfred, It floats: The story of Procter & Gamble, published 1958 by Rinehart.
- MacMillen, Harold W., Mr. Mac and Central Soya: the foodpower story, published 1967 by Newcomen Society
- Marchand, C.M. 1982. "Positional isomers of trans-octadecenoic acids in margarine." Canadian Institute of Food Science and Technology Journal. 15: 196-199.
- Mensink, R.P., Zock, P.L., Katan, M.B. and Hornstra, G. 1992. "Effect of dietary cis-and trans-fatty acids on serum lipoprotein[a] levels in humans." Journal of Lipid Research. 33: 1493-1501.
- Siguel, E.N. and Lerman, R.H. 1993. "Trans fatty acid patterns in patients with angiographically documented coronary artery disease." American Journal of Cardiology. 71: 916-920.
- Troisi, R., Willett, W.C. and Weiss, S.T. 1992. "Trans-fatty acid intake in relation to serum lipid concentrations in adult men." American Journal of Clinical Nutrition. 56: 1019-1024.
- Willett, W.C., Stampfer, M.J., Manson, J.E., Colditz, G.A., Speizer, F.E., Rosner, B.A., Sampson, L.A. and Hennekens, C.H. 1993. "Intake of trans fatty acids and risk of coronary heart disease among women." The Lancet. 341: 581-585.
External links
|