1.1 Vegetable oil

A vegetable oil is a triglyceride extracted from a plant. Such oils have been part of human culture for millennia. The term "vegetable oil" can be narrowly defined as referring only to substances that are liquid at room temperature, or broadly defined without regard to a substance's state of matter at a given temperature. For this reason, vegetable oils that are solid at room temperature are sometimes called vegetable fats. Vegetable oils are composed of triglycerides, as contrasted with waxes which lack glycerin in their structure. Although many plant parts may yield oil, in commercial practice, oil is extracted primarily from seeds.

1.2 Production of Vegetable Oils

To produce vegetable oils, the oil first needs to be removed from the oil-bearing plant components, typically seeds. This can be done via mechanical extraction using an oil mill or chemical extraction using a solvent. The extracted oil can then be purified and, if required, refined or chemically altered.

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1.2.1 Mechanical extraction

Oils can also be removed via mechanical extraction, termed "crushing" or "pressing." This method is typically used to produce the more traditional oils (e.g., olive, coconut etc.), and it is preferred by most health food customers in the United States and in Europe. There are several different types of mechanical extraction: expeller-pressing extraction is common, though the screw press, ram press, and Ghani (powered mortar and pestle) are also used. Oil seed presses are commonly used in developing countries, among people for whom other extraction methods would be prohibitively expensive; the Ghani is primarily used in India.

1.2.2 Solvent extraction

The processing of vegetable oil in commercial applications is commonly done 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. Supercritical carbon dioxide can be used as a non-toxic alternative to other solvents.

1.2.3 Sparging

In the processing of edible oils, the oil is heated under vacuum to near the smoke point, and water is introduced at the bottom of the oil. The water immediately is converted to steam, which bubbles through the oil, carrying with it any chemicals which are water-soluble. The steam sparging removes impurities that can impart unwanted flavors and odors to the oil.

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1.2.4 Hydrogenation

Oils may be partially hydrogenated to produce various ingredient oils. Lightly hydrogenated oils have very similar physical characteristics to regular soya oil, but are more resistant to 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. Hydrogenated oils, especially partially hydrogenated oils with their higher amounts of trans fatty acids are increasingly thought to be unhealthy.

1.3 Uses of triglyceride vegetable oil

The following are some of the uses of vegetable oils:

1)   Culinary uses: Many vegetable oils are consumed directly, or indirectly as ingredients in food – a role that they share with some animal fats, including butter and ghee;

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2)     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 oils, 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 .

3)    Pet food additive: Vegetable oil is used in production of some pet foods. In some poorer grade pet foods though, the oil is listed only as "vegetable oil", without specifying the particular oil.

4)     Fuel: Vegetable 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. It is believed that the total net greenhouse gas savings when using vegetable oils in place of fossil fuel-based alternatives for fuel production, range from 18 to 100% [10].

1.4 Negative health effects

Hydrogenated oils have been shown to cause what is commonly termed the "double deadly effect", raising the level of low density lipoproteins (LDLs) and decreasing the level of high density lipoproteins (HDLs) in the blood, increasing the risk of blood clotting inside blood vessels.

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A high consumption of omega-6 polyunsaturated fatty acids (PUFAs), which are

found in most types of vegetable oil (e.g. soyabean oil, corn oil– the most consumed in USA, sunflower oil, etc.) may increase the likelihood that postmenopausal women will develop breast cancer. A similar effect was observed on prostate cancer in mice. Plant based oils high in monounsaturated fatty acids, such as olive oil, peanut oil, and canola oil are relatively low in omega-6 PUFAs and can be used in place of high-polyunsaturated oils.

1.5 Uses/Importance of Vegetable oils

1.5.1 Margarine

Margarine originated with the discovery by French chemist Michel Eugene Chereul in 1813 of margaric acid (itself named after the pearly deposits of the fatty acid from Greek (margaritēs / márgaron), meaning pearl-oyster or pearl, or (margarís), meaning palm-tree, hence the relevance to palmitic acid). Scientists at the time regarded margaric acid, like oleic acid and stearic acid, as one of the three fatty acids which, in combination, formed most animal fats. In 1853, the German structural chemist Wihelm Heinrich Heintz analyzed margaric acid as simply a combination of stearic acid and of the previously unknown palmitic acid.

Emperor Louis Napoleon III of France offered a prize to anyone who could make a satisfactory substitute for butter, suitable for use by the armed forces and the lower classes. French chemist Hippolyte Mege-Mouries invented a substance he called oleomargarine, the name of which became shortened to the trade name "margarine". Mège-Mouriès patented the concept in 1869 and expanded his initial manufacturing

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