Vegetable fats and oils are lipid materials derived from plants. Physically, oils are liquid at room temperature, and fats are solid. Chemically, both fats and oils are composed of triglycerides, as contrasted with waxes which lack glycerin in their structure. Although many different parts of plants may yield oil, in commercial practice, oil is extracted primarily from seeds.
The melting temperature distinction between oils and fats is imprecise, since definitions of room temperature vary, and typically natural oils have a melting range instead of a single melting point.
Vegetable fats and oils may be edible or inedible. Examples of inedible vegetable fats and oils include processed linseed oil, tung 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, fats and oils also typically contain free fatty acids, monoglycerides, and diglycerides.
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.
Culinary uses
See also: Cooking oilMany 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:
- Shortening - to give pastry a crumbly texture .
- 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" 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, safflower, peanut etc. Tropical oils, like palm oil, coconut oil and rice bran oil, are particularly valued in Asian cultures for high temperature cooking, because of their unusually high flash point.
Hydrogenated oils
Unsaturated vegetable fats and oils can be transformed through partial or complete hydrogenation into fats and oils of higher melting point. 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 is broken, two hydrogen atoms each form single bonds with the two carbon atoms. 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. An oil may be hydrogenated to increase resistance to rancidity (oxidation) or to change its physical characteristics. As the degree of saturation increases, the oil's viscosity and melting point increase.
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 fatty acids, most of the hydrogenation occurs on the end fatty acids. This makes the resulting fat more brittle. A margarine made from naturally more saturated oils will be more plastic (more "spreadable") than a margarine made from, say, hydrogenated soy oil. In addition, partial hydrogenation results in the formation of large amounts of trans fats in the oil mixture, which, since the 1970s, have increasingly been viewed as unhealthy.
(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. Products not labeled vegetable oil margarine do not have that restriction.)
Industrial uses
Vegetable oils are used as an ingredient or component in many manufactured products.
- Many vegetable oils are used to make soaps, skin products, candles, 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 (a mixture of linseed oil and dammar resin), 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 are less chemically-stable, so they are generally used in systems where they are not exposed to oxygen, and they are more expensive than crude oil distillate. Two examples are FR3 by Cooper Power and Biotemp by ABB. Midel 7131 by M & I materials is a synthetic tetraester, like a vegetable oil but with four fatty acid chains compared to the normal three found in a natural ester, and is manufactured by an alcohol plus acid reaction. Tetraesters generally have high stability to oxidation and have found use as engine lubricants.
- Vegetable oil is being used to produce bio-degradable hydraulic fluid and lubricant.
- 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 chemically decompose turning rancid. Oils that are more stable, such as Ben oil or mineral oil, are preferred for some industrial uses.
Vegetable-based oils, like castor oil, have been used as medicine and as lubricants for a long time. Castor oil has numerous industrial uses, primarily due to the presence of hydroxyl groups on the fatty acid chains. Castor oil, and other vegetable oils which have been chemically modified to contain hydroxyl groups, are becoming increasingly important in the production of polyurethane plastic for many applications. These modified vegetable oils are known as natural oil polyols.
Pet food additive
Vegetable oil is used in production of some pet foods. AAFCO defines vegetable oil, in this context, as the product of vegetable origin obtained by extracting the oil from seeds or fruits which are processed for edible purposes. In some poorer grade pet foods, the oil is listed only as "vegetable oil", without specifying the particular oil.
Fuel
Main article: Vegetable oil used as fuelVegetable oils are also used to make biodiesel, which can be used like conventional diesel. Some vegetable oil blends are used in unmodified vehicles but straight vegetable oil, also known as pure plant oil, needs specially prepared vehicles which have a method of heating the oil to reduce its viscosity. The vegetable oil economy is growing and the availability of biodiesel around the world is increasing.
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. The amount of oil extracted using these methods varies widely, as shown in the following table for extracting mowrah butter in India:
Supercritical carbon dioxide can also be used for the extraction purpose and is non toxic.
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 triglycerides 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.
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