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<p> </p><p>INTRODUCTION<br>EXTRACTION AND CHARACTERIZATION OF VEGETABLE OIL USING<br>BREAD FRUIT SEED.<br>1.1 Vegetable oil<br>A vegetable oil is a triglyceride extracted from a plant. Such oils have been part of<br>human culture for millennia. The term “vegetable oil” can be narrowly defined as<br>referring only to substances that are liquid at room temperature, or broadly defined<br>without regard to a substance’s state of matter at a given temperature. For this reason,<br>vegetable oils that are solid at room temperature are sometimes called vegetable fats.<br>Vegetable oils are composed of triglycerides, as contrasted with waxes which lack<br>glycerin in their structure. Although many plant parts may yield oil, in commercial<br>practice, oil is extracted primarily from seeds.<br>1.2 Production of Vegetable Oils<br>To produce vegetable oils, the oil first needs to be removed from the oil-bearing<br>plant components, typically seeds. This can be done via mechanical extraction using an<br>oil mill or chemical extraction using a solvent. The extracted oil can then be purified and,<br>if required, refined or chemically altered.</p><p>2<br>1.2.1 Mechanical extraction<br>Oils can also be removed via mechanical extraction, termed “crushing” or<br>“pressing.” This method is typically used to produce the more traditional oils (e.g., olive,<br>coconut etc.), and it is preferred by most health food customers in the United States and<br>in Europe. There are several different types of mechanical extraction: expeller-pressing<br>extraction is common, though the screw press, ram press, and Ghani (powered mortar and<br>pestle) are also used. Oil seed presses are commonly used in developing countries, among<br>people for whom other extraction methods would be prohibitively expensive; the Ghani is<br>primarily used in India.<br>1.2.2 Solvent extraction<br>The processing of vegetable oil in commercial applications is commonly done by<br>chemical extraction, using solvent extracts, which produces higher yields and is quicker<br>and less expensive. The most common solvent is petroleum-derived hexane. This<br>technique is used for most of the “newer” industrial oils such as soybean and corn oils.<br>Supercritical carbon dioxide can be used as a non-toxic alternative to other solvents.<br>1.2.3 Sparging<br>In the processing of edible oils, the oil is heated under vacuum to near the smoke<br>point, and water is introduced at the bottom of the oil. The water immediately is<br>converted to steam, which bubbles through the oil, carrying with it any chemicals which<br>are water-soluble. The steam sparging removes impurities that can impart unwanted<br>flavors and odors to the oil.<br>3<br>1.2.4 Hydrogenation<br>Oils may be partially hydrogenated to produce various ingredient oils. Lightly<br>hydrogenated oils have very similar physical characteristics to regular soya oil, but are<br>more resistant to becoming rancid. Hardening vegetable oil is done by raising a blend of<br>vegetable oil and a catalyst in near-vacuum to very high temperatures, and introducing<br>hydrogen. This causes the carbon atoms of the oil to break double-bonds with other<br>carbons, each carbon forming a new single-bond with a hydrogen atom. Adding these<br>hydrogen atoms to the oil makes it more solid, raises the smoke point, and makes the oil<br>more stable.<br>Hydrogenated vegetable oils differ in two major ways from other oils which are<br>equally saturated. During hydrogenation, it is easier for hydrogen to come into contact<br>with the fatty acids on the end of the triglyceride, and less easy for them to come into<br>contact with the center fatty acid. This makes the resulting fat more brittle than a tropical<br>oil; soy margarines are less “spreadable”. The other difference is that trans fatty acids<br>(often called trans fat) are formed in the hydrogenation reactor, and may amount to as<br>much as 40 percent by weight of a partially hydrogenated oil. Hydrogenated oils,<br>especially partially hydrogenated oils with their higher amounts of trans fatty acids are<br>increasingly thought to be unhealthy.<br>1.3 Uses of triglyceride vegetable oil<br>The following are some of the uses of vegetable oils:<br>1) Culinary uses: Many vegetable oils are consumed directly, or indirectly as ingredients<br>in food – a role that they share with some animal fats, including butter and ghee;<br>4 2) Industrial uses: Vegetable oils are used as an ingredient or component in many<br>manufactured products. Many vegetable oils are used to make soaps, skin products,<br>candles, perfumes and other personal care and cosmetic products. Some oils are<br>particularly suitable as drying oils, and are used in making paints and other wood<br>treatment products. Dammar oil (a mixture of linseed oil and dammar resin), for example,<br>is used almost exclusively in treating the hulls of wooden boats. Vegetable oils are<br>increasingly being used in the electrical industry as insulators .<br>3) Pet food additive: Vegetable oil is used in production of some pet foods. In some<br>poorer grade pet foods though, the oil is listed only as “vegetable oil”, without specifying<br>the particular oil.<br>4) Fuel: Vegetable oils are also used to make biodiesel, which can be used like<br>conventional diesel. Some vegetable oil blends are used in unmodified vehicles but<br>straight vegetable oil, also known as pure plant oil, needs specially prepared vehicles<br>which have a method of heating the oil to reduce its viscosity. The vegetable oil economy<br>is growing and the availability of biodiesel around the world is increasing. It is believed<br>that the total net greenhouse gas savings when using vegetable oils in place of fossil fuel<br>based alternatives for fuel production, range from 18 to 100% [10].<br>1.4 Negative health effects<br>Hydrogenated oils have been shown to cause what is commonly termed the<br>“double deadly effect”, raising the level of low density lipoproteins (LDLs) and<br>decreasing the level of high density lipoproteins (HDLs) in the blood, increasing the risk<br>of blood clotting inside blood vessels.<br>5 A high consumption of omega-6 polyunsaturated fatty acids (PUFAs), which are<br>found in most types of vegetable oil (e.g. soyabean oil, corn oil– the most consumed in<br>USA, sunflower oil, etc.) may increase the likelihood that postmenopausal women will<br>develop breast cancer. A similar effect was observed on prostate cancer in mice. Plant<br>based oils high in monounsaturated fatty acids, such as olive oil, peanut oil, and canola<br>oil are relatively low in omega-6 PUFAs and can be used in place of high<br>polyunsaturated oils.<br>1.5 Uses/Importance of Vegetable oils<br>1.5.1 Margarine<br>Margarine originated with the discovery by French chemist Michel Eugene<br>Chereul in 1813 of margaric acid (itself named after the pearly deposits of the fatty acid<br>from Greek (margaritÄ“s / márgaron), meaning pearl-oyster or pearl, or (margarís),<br>meaning palm-tree, hence the relevance to palmitic acid). Scientists at the time regarded<br>margaric acid, like oleic acid and stearic acid, as one of the three fatty acids which, in<br>combination, formed most animal fats. In 1853, the German structural chemist Wihelm<br>Heinrich Heintz analyzed margaric acid as simply a combination of stearic acid and of<br>the previously unknown palmitic acid.<br>Emperor Louis Napoleon III of France offered a prize to anyone who could make<br>a satisfactory substitute for butter, suitable for use by the armed forces and the lower<br>classes. French chemist Hippolyte Mege-Mouries invented a substance he called<br>oleomargarine, the name of which became shortened to the trade name “margarine”.<br>Mège-Mouriès patented the concept in 1869 and expanded his initial manufacturing<br>6 operation from France but had little commercial success. In 1871, he sold the patent to<br>the Dutch company Jurgens, now part of Unilever. In the same year the German<br>pharmacist Benedict Klein from Cologne founded the first margarine factory “Benedict<br>Klein Margarinewerke”, producing the brands Overstolz and Botteram.<br>Margarine is a semi-solid emulsion composed mainly of vegetable fats and water.<br>While butter is derived from milk fat, margarine is mainly derived from plant oils and<br>fats and may contain some skimmed milk. In some locales it is colloquially referred to as<br>oleo, short for oleomargarine. Margarine, like butter, consists of a water-in-fat emulsion,<br>with tiny droplets of water dispersed uniformly throughout a fat phase which is in a stable<br>crystalline form. Margarine has a minimum fat content of 80%, the same as butter, but<br>unlike butter reduced-fat varieties of margarine can also be labelled as margarine.<br>Margarine can be used both for spreading or for baking and cooking. It is also commonly<br>used as an ingredient in other food products, such as pastries and cookies, for its wide<br>range of functionalities.<br>1.5.1.2 Manufacture of Margarine<br>The basic method of making margarine today consists of emulsifying a blend of<br>hydrogenated vegetable oils with skimmed milk, chilling the mixture to solidify it and<br>working it to improve the texture. Vegetable and animal fats are similar compounds with<br>different melting points. Those fats that are liquid at room temperature are generally<br>known as oils. The melting points are related to the presence of carbon-carbon double<br>bonds in the fatty acids components. Higher number of double bonds give lower melting<br>points.<br>7<br>Figure 1: Hydrogenation of vegetable oils</p><p>Partial hydrogenation of a typical plant oil to a typical component of margarine,<br>makes most of the C=C double bonds be removed in this process, which elevates the<br>melting point of the product. Commonly, the natural oils are hydrogenated by passing<br>hydrogen through the oil in the presence of a nickel catalyst, under controlled conditions.<br>The addition of hydrogen to the unsaturated bonds (alkenic double C=C bonds) results in<br>saturated C-C bonds, effectively increasing the melting point of the oil and thus<br>“hardening” it. This is due to the increase in van der Waals’ forces between the saturated<br>molecules compared with the unsaturated molecules. However, as there are possible<br>health benefits in limiting the amount of saturated fats in the human diet, the process is<br>controlled so that only enough of the bonds are hydrogenated to give the required texture.<br>Margarines manufactured in this way are said to contain hydrogenated fat. This method is<br>used today for some margarines although the process has been developed and sometimes<br>8 other metal catalysts are used such as palladium. If hydrogenation is incomplete (partial<br>hardening), the relatively high temperatures used in the hydrogenation process tend to<br>flip some of the carbon-carbon double bonds into the “trans” form. If these particular<br>bonds aren’t hydrogenated during the process, they will still be present in the final<br>margarine in molecules of trans fats, the consumption of which has been shown to be a<br>risk factor for cardiovascular disease. For this reason, partially hardened fats are used less<br>and less in the margarine industry. Some tropical oils, such as palm oil and coconut oil,<br>are naturally semi solid and do not require hydrogenation.<br>Three types of margarine are common:<br>ï‚· Soft vegetable fat spreads, high in mono- or polyunsaturated fats, which are made<br>from safflower, sunflower, soybean, cottonseed, rapeseed or olive oil.<br>ï‚· Margarines in bottle to cook or top dishes<br>ï‚· Hard, generally uncolored margarine for cooking or baking.<br>1.5.2 Soap<br>In chemistry, soap is a salt of a fatty acid. Soaps are mainly used as surfactants for<br>washing, bathing, cleaning, in textile spinning and are important components of<br>lubricants. Soaps for cleansing are obtained by treating vegetable or animal oils and fats<br>with a strongly alkaline solution. Fats and oils are composed of triglycerides; three<br>molecules of fatty acids are attached to a single molecule of glycerol. The alkaline<br>solution, which is often called lye, (although the term “lye soap” refers almost<br>exclusively to soaps made with sodium hydroxide) brings about a chemical reaction<br>known as saponification. In saponification, the fats are first hydrolyzed into free fatty<br>acids, which then combine with the alkali to form crude soap. Glycerol (glycerin) is<br>9 liberated and is either left in or washed out and recovered as a useful byproduct,<br>depending on the process employed.<br>When used for cleaning, soap allows otherwise insoluble particles to become<br>soluble in water and then be rinsed away. For example: oil/fat is insoluble in water, but<br>when a couple drops of dish soap are added to the mixture the oil/fat apparently<br>disappears. The insoluble oil/fat molecules become associated inside micelles, tiny<br>spheres formed from soap molecules with polar hydrophilic (water-loving) groups on the<br>outside and encasing a lipophilic (fat-loving) pocket, which shielded the oil/fat molecules<br>from the water making it soluble. Anything that is soluble will be washed away with the<br>water. Synthetic detergents operate by similar mechanisms to soap.<br>The type of alkali metal used determines the kind of soap produced. Sodium<br>soaps, prepared from sodium hydroxide, are firm, whereas potassium soaps, derived from<br>potassium hydroxide, are softer or often liquid. Historically, potassium hydroxide was<br>extracted from the ashes of bracken or other plants. Lithium soaps also tend to be hard<br>these are used exclusively in greases.<br>Typical vegetable oils used in soap making are palm oil, coconut oil, olive oil,<br>and laurel oil. Each species offers quite different fatty acid content and, hence, results in<br>soaps of distinct feel. The seed oils give softer but milder soaps. Soap made from pure<br>olive oil is sometimes called Castile/Marseille soap, and is reputed for being extra mild.<br>The term “Castile” is also sometimes applied to soaps from a mixture of oils, but a high<br>percentage of olive oil.</p><p>10<br>1.5.2.1 Purification and finishing</p><p>Figure 2: A generic bar of soap, after purification and finishing<br>In the fully boiled process on factory scale, the soap is further purified to remove<br>any excess sodium hydroxide, glycerol, and other impurities, colour compounds, etc.<br>These components are removed by boiling the crude soap curds in water and then<br>precipitating the soap with salt. At this stage, the soap still contains too much water,<br>which has to be removed. This was traditionally done on chill rolls, which produced the<br>soap flakes commonly used in the 1940s and 1950s. This process was superseded by<br>spray dryers and then by vacuum dryers. The dry soap (about 6–12% moisture) is then<br>compacted into small pellets or noodles. These pellets or noodles are then ready for soap<br>finishing, the process of converting raw soap pellets into a saleable product, usually bars.<br>Soap pellets are combined with fragrances and other materials and blended to<br>homogeneity in an amalgamator (mixer). The mass is then discharged from the mixer into<br>a refiner, which, by means of an auger, forces the soap through a fine wire screen. From<br>the refiner, the soap passes over a roller mill (French milling or hard milling) in a manner<br>similar to calendering paper or plastic or to making chocolate liquor. The soap is then<br>11 passed through one or more additional refiners to further plasticize the soap mass.<br>Immediately before extrusion, the mass is passed through a vacuum chamber to remove<br>any trapped air. It is then extruded into a long log or blank, cut to convenient lengths,<br>passed through a metal detector, and then stamped into shape in refrigerated tools. The<br>pressed bars are packaged in many ways.<br>Sand or pumice may be added to produce a scouring soap. The scouring agents serve to<br>remove dead cells from the skin surface being cleaned. This process is called exfoliation.<br>Many newer materials that are effective, yet do not have the sharp edges and poor particle<br>size distribution of pumice, are used for exfoliating soaps.<br>Nanoscopic metals are commonly added to certain soaps specifically for both colouration<br>and antibacterial properties. Titanium dioxide powder is commonly used in extreme<br>“white” soaps for these purposes; nickel, aluminium and silver compounds are less<br>commonly used. These metals exhibit an electron-robbing behaviour when in contact<br>with bacteria, stripping electrons from the organism’s surface, thereby disrupting their<br>functioning and killing them. Since some of the metal is left behind on the skin and in the<br>pores, the benefit can also extend beyond the actual time of washing, helping reduce<br>bacterial contamination and reducing potential odours from bacteria on the skin surface.<br>1.5.3 Biodiesel production<br>Biodiesel production is the process of producing the biofuel/biodiesel, through the<br>chemical reactions: transesterification and esterification. This involves vegetable or<br>animal fats and oils being reacted with short-chain alcohols (typically methanol or<br>ethanol). The major steps required to synthesize biodiesel are as follows:<br>12 1. Feedstock pretreatment: Common feedstock used in biodiesel production<br>include yellow grease (recycled vegetable oil), “virgin” vegetable oil, and tallow.<br>Recycled oil is processed to remove impurities from cooking, storage, and<br>handling, such as dirt, charred food, and water. Virgin oils are refined, but not to a<br>food-grade level. De-gumming to remove phospholipids and other plant matter is<br>common, though refinement processes vary. Regardless of the feedstock, water is<br>removed as its presence during base-catalyzed transesterification causes the<br>triglycerides to hydrolyse, giving salts of the fatty acids (soaps) instead of<br>producing biodiesel.<br>2. Determination and treatment of free fatty acids: A sample of the cleaned<br>feedstock oil is titrated with a standardized base solution in order to determine the<br>concentration of free fatty acids (carboxylic acids) present in the vegetable oil<br>sample. These acids are then either esterified into biodiesel, esterified into<br>glycerides, or removed, typically through neutralization.<br>3. Reactions: Base-catalyzed transesterification reacts lipids (fats and oils) with<br>alcohol (typically methanol or ethanol) to produce biodiesel and an impure co<br>product, glycerol. If the feedstock oil is used or has a high acid content, acid<br>catalyzed esterification can be used to react fatty acids with alcohol to produce<br>biodiesel. Other methods, such as fixed-bed reactors, supercritical reactors, and<br>ultrasonic reactors, forgo or decrease the use of chemical catalysts.<br>4. Product purification: Products of the reaction include not only biodiesel, but<br>also byproducts, soap, glycerol, excess alcohol, and trace amounts of water. All of<br>these byproducts must be removed to meet the standards, but the order of removal<br>is process-dependent. The density of glycerol is greater than that of biodiesel, and<br>13 this property difference is exploited to separate the bulk of the glycerol co<br>product. Residual methanol is typically recovered by distillation and reused.<br>Soaps can be removed or converted into acids. Residual water is also removed<br>from the fuel.<br>1.5.3.1 Reactions<br>Animal and plant fats and oils are composed of triglycerides, which are esters<br>containing three free fatty acids and the trihydric alcohol, glycerol. In the<br>transesterification process, the alcohol is de-protonated with a base to make it a stronger<br>nucleophile. Commonly, ethanol or methanol are used. As can be seen, the reaction has<br>no other inputs than the triglyceride and the alcohol. Under normal conditions, this<br>reaction will proceed either exceedingly slowly or not at all, so heat, as well as catalysts<br>(acid and/or base) are used to speed up the reaction. It is important to note that the acid or<br>base are not consumed by the transesterification reaction, thus they are not reactants, but<br>catalysts. Common catalysts for transesterification include sodium hydroxide, potassium<br>hydroxide, and sodium methoxide.<br>Almost all biodiesel is produced from virgin vegetable oils using the base<br>catalyzed technique as it is the most economical process for treating virgin vegetable oils,<br>requiring only low temperatures and pressures and producing over 98% conversion yield<br>(provided the starting oil is low in moisture and free fatty acids). However, biodiesel<br>produced from other sources or by other methods may require acid catalysis, which is<br>much slower.<br>14 The transesterification reaction is base catalyzed. Any strong base capable of de<br>protonating the alcohol will do (e.g. NaOH, KOH, sodium methoxide, etc.), but the<br>sodium and potassium hydroxides are often chosen for their cost. The presence of water<br>causes undesirable base hydrolysis, so the reaction must be kept dry. In the<br>transesterification mechanism, the carbonyl carbon of the starting ester (RCOOR1)<br>undergoes nucleophilic attack by the incoming alkoxide (R2O−) to give a tetrahedral<br>intermediate, which either reverts to the starting material, or proceeds to the<br>transesterified product (RCOOR2). The various species exist in equilibrium, and the<br>product distribution depends on the relative energies of the reactant and product.<br>GENERAL PROPERTIES OF VEGETABLE OILS<br>1.6 Vegetable oils – General properties</p><p>Vegetable oils are obtained from oil containing seeds, fruits, or nuts by different pressing<br>methods, solvent extraction or a combination of these (Bennion, 1995). Crude oils<br>obtained are subjected to a number of refining processes, both physical and chemical.<br>These are detailed in various texts and articles (Bennion, 1995), (Fennema, 1985). There<br>are numerous vegetable oils derived from various sources. These include the popular<br>vegetable oils: the foremost oilseed oils – soybean, cottonseed, peanuts and sunflower<br>oils; and others such as palm oil, palm kernel oil, coconut oil, castor oil, rapeseed oil and<br>others. They also include the less commonly known oils such as rice bran oil, tiger nut<br>oil, patua oil, ko_me oil, niger seed oil, piririma oil and numerous others. Their yields,<br>different compositions and by extension their physical and chemical properties determine<br>their usefulness in various applications aside edible uses.</p><p>15 Cottonseed oil was developed over a century ago as a byproduct of the cotton industry<br>(Bennion, 1995). Its processing includes the use of hydraulic pressing, screw pressing<br>and solvent extraction (Wolf, 1978). It is classified as a polyunsaturated oil, with palmitic<br>acid (C16H32O2) consisting 20 – 25%, stearic acid (C18H36O2) 2 – 7%, oleic acid<br>(C18H34O2) 18 – 30%, and linoleic acid (C18H32O2)40 – 55% (Fennema, 1985). Its<br>primary uses are food related – as salad oil, for frying, for margarine manufacture, and<br>for manufacturing shortenings used in cakes and biscuits.<br>Palm oil, olive oil, cottonseed oil, peanut oil, and sunflower oil amongst others are<br>classed as Oleic – Linoleic acid oils seeing that they contain a relatively high proportion<br>of unsaturated fatty acids, such as the monounsaturated oleic acid and the<br>polyunsaturated linoleic acid (Dunn, 2005; Gertz et al., 2000). They are characterized by<br>a high ratio of polyunsaturated fatty acids to saturated fatty acids. As a consequence of<br>this, they have relatively low melting points and are liquid at room temperature. Iodine<br>values, saponification values, specific compositions and melting points in addition to<br>other physical properties have been determined and are widely available in the literature<br>(Williams, 1966), (Oyedeji et al., 2006).<br>Other oils fall under various classes such as the erucic acid oils which are like the oleic<br>linoleic acid oils except that their predominant unsaturated fatty acid is erucic acid (C22).<br>Rapeseed and mustard seed oil are important oils in this class. Canola oil is a type of<br>rapeseed oil with reduced erucic acid content (Applewhite, 1978). It is a stable oil used in<br>salad dressings, margarine and shortenings. Soybean oil is an important oil with<br>numerous increasing applications in the modern day world. It is classed as a linolenic<br>acid oil since it contains the more highly unsaturated linolenic acid. Other oils include<br>castor oil (a hydroxy-acid oil) which contains glycerides of ricinoleic acid (Erhan et al.,<br>16 2006). Also worthy of note is that coconut oil, which unlike most vegetable oils, is solid<br>at room temperature due to its high proportion of saturated fatty acids (92%) particularly<br>lauric acid. Due to its almost homogenous composition, coconut oil has a fairly sharp<br>melting point (Bennion, 1995).</p><p>1.7 Auto oxidation and oxidative stability in vegetable oils<br>By definition, the oxidative stability of oil is a measure of the length of time taken for<br>oxidative deterioration to commence. On a general level, “the rates of reactions in auto<br>oxidation schemes are dependent on the hydrocarbon structure, heteroatom concentration,<br>heteroatom speciation, oxygen concentration, and temperature (Ferrari et al., 2004).<br>If untreated, oils from vegetable origin oxidize during use and polymerize to a plastic like<br>consistency (Honary, 2004). Even when they are not subjected to the intense conditions<br>of industrial applications, fats and oils are liable to rancidity (Eastman Chemical<br>Company, 2001; Morteza- Semnani et al., 2006). This happens more so in fats that<br>contain unsaturated fatty acid radicals (Charley,<br>1970). Indeed the oxidisability of a vegetable oil is dependent on the level of unsaturation<br>of their olefinic compounds. In general terms, oxidative rancidity in oils occurs when<br>heat, metals or other catalysts cause unsaturated oil molecules to convert to free radicals.<br>These free radicals are easily oxidized to yield hydroperoxides and organic compounds,<br>such as aldehydes, ketones, or acids which give rise to the undesirable odors and flavors<br>characteristic of rancid fats (Eastman Chemical Company, 2001). The role of peroxides is<br>exploited in monitoring oxidative deterioration by measuring peroxide values (POV)<br>(Mochida et al., 2006).</p><p>17 Lipid oxidation occurs via auto oxidation or lipoxygenase catalysis. Auto oxidation refers<br>to a complex set of reactions which result in the incorporation of oxygen in lipid<br>structures. Auto oxidation reactions are seen to progress more rapidly in oils that contain<br>predominantly unsaturated fat molecules; other relevant factors include the presence of<br>light, transition metal ions, oxygen pressure, the presence or absence of antioxidants and<br>pro oxidants, temperature and moisture content. Auto oxidation reactions occur at an<br>increasing rate after the initial induction period. This behavior can be explained by<br>assuming that oxidation proceeds by a sequential free radical chain reaction mechanism.<br>Relatively stable radicals that can abstract hydrogen atoms from the allylic methylene<br>groups in olefinic compounds are formed. Hence auto oxidation is a radical induced chain<br>reaction which proceeds through the traditional stages of initiation, propagation and<br>termination. Detailed proposed mechanisms for these free radical chain reactions are<br>available in literature (Fennema, 1985).<br>Lipoxygenases are metal proteins with an iron atom as the active center. They catalyze<br>the oxidation of unsaturated fatty acids to hydroperoxides as with auto oxidation. Enzyme<br>activation usually occurs in the presence of hydroperoxides, even though enzyme<br>catalyzed oxidation can occur even in the absence of hydroperoxides (Fennema, 1985).<br>As earlier stated, the more unsaturated the fatty acid involved is, the greater its<br>susceptibility to oxidative rancidity. For instance, the linolenic acid esters present in<br>soybean oil (with twice the unsaturation as monounsaturated esters) is particularly<br>sensitive to even oxidation of the slightest kind, commonly referred to as flavor<br>reversion, resulting in beany, grassy or painty flavors (Wolf, 1978). A highly saturated<br>fatty acid level is confirmed to be of benefit in terms of storage ability when compared to<br>more unsaturated vegetable oils (Ferrari et al., 2004). Indeed, the tendency of an oil to<br>18 combine with oxygen of the air and become gummy (known as drying) is measured with<br>the iodine number, which in fact is merely a measure of the level of unsaturation of the<br>oil in question (a higher iodine number will indicate higher unsaturation seeing that<br>iodine is absorbed primarily by the mechanism of addition to the double bonds<br>characteristic of unsaturation) (Gunther, 1971).<br>Based on studies by Toshiyuki. (1999), the oxidative stability of refined vegetable oils is<br>found to be determined considerably by the fatty acid composition, the tocopherols<br>content and the carbonyl value (Toshiyuki, 1999). When observed at frying temperatures,<br>it is seen that in general, non-refined oils prove to have a better stability than refined oils<br>(Gertz et al., 2000). This could be attributed to the fact that refining steps, in particular<br>deodorization, remove a percentage of the tocopherols, which act as natural anti-oxidants<br>in vegetable oils (Applewhite, 1978). Corn oil has a better stability than soybean oil,<br>while rapeseed oil is seen to give a better performance than olive oil. This can be<br>explained in terms of their compositions (Isbell et al., 1999). When investigated at a<br>temperature of 110oC, vegetable oils still show the trend of increased stability in the<br>unrefined state than when refined. Meadow foam oil is reported as the most stable oil in<br>the study conducted by Isbell et al. (1999). High oleic sunflower oil and crude jojoba oil<br>also had good values of oxidative stability (Isbell et al., 1999). Other studies indicate that<br>the presence of free fatty acids has a pro-oxidant effect on vegetable oils (Frega et al.,<br>1999). Hence refining practices are important, seeing Aluyor and Ori-Jesu 4839 that<br>improper handling and raw material abuse can result in the stimulation of enzymatic<br>activity which could produce free fatty acids (Applewhite, 1978). Further investigations<br>on manufacturing practices also reveal research which indicates the importance of the<br>solvent used in the extraction of vegetable oils. Traditional solvents utilized such as<br>19 hexane or petroleum ether have the characteristic of extracting only non-polar species.<br>Isopropanol however, as documented by Oyedeji et al. (2006) would extract some polar<br>and high molecular weight compounds. Among these compounds are the natural<br>antioxidants and pigments in oilseeds which presence lead to extended shelf life and<br>hence better oxidative stability (Oyedeji et al., 2006).</p><p>1.8 Antioxidants and stability of vegetable oils<br>Numerous experimental works have established the positive effect of anti-oxidants on the<br>oxidative stability of vegetable oils for both edible uses and industrial uses. An important<br>class of anti-oxidants consists of the phenolic compounds butylhydroxyanisole (BHA),<br>butylhydroxytoluene (BHT), propyl gallate, and tert-butyl<br>hydroquinone (TBHQ). Their use in vegetable oils meant for domestic and industrial<br>processes is widespread.<br>Vegetable oils in their natural form possess constituents that function as natural<br>antioxidants. Amongst them are ascorbic acids, _-tocopherole, _-carotene, chlorogenic<br>acids and flavanols (Ullah et al., 2003). Tests conducted to investigate the effectiveness<br>of natural anti-oxidants contained in red pepper oil added to soybean and sunflower oils<br>indicate that they provide variable protection against light induced auto-oxidation.<br>In the above mentioned study on the inhibitive effect of natural antioxidants contained in<br>red pepper oil, it was additionally observed that the phenolic anti-oxidant<br>butylated hydroxytoluene (BHT) shows more effectiveness generally than natural anti<br>oxidants (Ullah et al., 2003). In the work done by Robert (2005), the common phenolic<br>anti-oxidants were tested for their effectivenessin improving the oxidative stability of<br>biodiesel obtained from soybean oil. Dunn monitored the oxidative stability by means of<br>20 pressurized differential scanning calorimetry (P-DSC). For both static and dynamic<br>conditions, improvements in oxidative stability are observed with the application of anti<br>oxidants, which included BHA, BHT, TBHQ, propyl gallate (PrG) and α-tocopherol. The<br>work of (Dunn, 2005) further showed that the relative effectiveness of the different anti<br>oxidants differed for static and dynamic conditions, although all showed superior<br>performance when compared with α-tocopherol.<br>A recent area of interest in antioxidant research is concerned with finding effective<br>replacements for the conventional synthetic antioxidants from among various natural<br>extracts from plant species which are seen to possess antioxidant properties. Such<br>research is in the main prompted by the reported possibility of synthetic antioxidants<br>having adverse health effects on humans exposed to them. Specifically, they are known<br>to contribute to liver enlargement and an increase in microsomal activity (Khanahmadi et<br>al., 2006; Morteza- Semnani et al., 2006). Maduka et al. (2003) investigated the<br>effectiveness of a Nigerian alcoholic beverage additive, Sacoglottis gabonensis stem bark<br>extract as an antioxidant for common stored vegetable oils. Inhibition of lipid peroxi<br>dation was found to be comparable to inhibitions obtained with treatment with vitamins C<br>and E (Maduka et al., 2003). The Ferulago angulata plant indigenous to the west of<br>Iran also has proven antioxidant properties. Experimental studies documented indicate<br>that these plants’ essential oils and extract begins to show preservative properties on<br>vegetable oils at a minimum concentration of 0.02%. In fact, it even shows more<br>effectiveness that TBHQ at concentrations of 0.5% (Khanahmadi et al., 2006). When<br>evaluated by measuring reducing power, ability to inhibit linoleic acid peroxidation, and<br>2,2-diphenyl picrylhydrazyl radical scavenging activities, the alkaloid extracts of<br>Fumaria capreolata and Fumaria bastardii demonstrated strong total antioxidant<br>21 activity, with effectiveness marginally less than that of the common synthetic antioxidant<br>butylated hydroxyanisole, and better than quercetine and caffeine. These species have<br>wide distribution in the Mediterranean region and have a reputation for effectiveness in<br>treating hepatobiliary disfunction and gastrointestinal disorders via local therapies (Maiza<br>et al., 2007). Methanolic extracts of Phlomis bruguieri, P. herbaventi, P. olivieri, Stachys<br>byzantine, S. inflata, S. lavandulifolia and S. laxa were tested in sunflower oil stored at<br>70oC for antioxidant effectiveness, using peroxide values as a measure. Comparisons<br>included samples containing BHA. Highest effectiveness in stabilizing sunflower was<br>obtained from methanolic extracts of P. bruguieri, and S. laxa. These tests and their<br>findings suggest strongly the possibility of having in these plants a viable source of<br>natural antioxidants of high performance (Morteza- Semnani et al., 2006).</p><p>1.9 Vegetable oils as lubricants, bio-fuels, and transformer coolants<br>The application of vegetable oils and animal fats for industrial purposes, and specifically<br>lubrication has been in practice for many years. Inherent disadvantages and the<br>availability of inexpensive options have however brought about low utilization of<br>vegetable oils for industrial lubrication (Honary, 2004). When applied in the science of<br>tribology, vegetable oils fall under the class known as fixed oils (Gunther, 1971). They<br>are so named because they do not volatilize without decomposing. Prior to recent<br>developments, vegetable and animal oils in tribology have functioned mainly as additives<br>to mineral lubricating oil formulations, although in some cases they are applied<br>exclusively, or in blends. For instance, tallow (acidless) has been used as an emulsifying<br>agent for steam cylinder oils, while castor, peanut and rapeseed oils have been used in<br>blends with mineral oils to improve lubrication performance. Palm oil has been used in<br>22 isolation as a fluxing dip in the tin plating of steel, while olive oil has applications as a<br>yarn lubricant (Gunther, 1971).<br>Reasons for the use of vegetable oils in the science of lubrication abound. Their superior<br>lubricity and emulsifying characteristics increase their desirability as additives to the<br>cheaper but less effective mineral oil aced lubricants. Their superior lubricity in industrial<br>and machinery lubrication sometimes even necessitates the addition of friction materials<br>in tractor transmissions in order to reduce clutch slippage (Honary, 2004).<br>Other advantages that encourage the use of vegetable oils include their relatively low<br>viscosity-temperature variation; that is their high viscosity indices, which are about twice<br>those of mineral oils (Honary, 2004). Additionally, they have low volatilities as<br>manifested by their high flash points (Honary, 2004). Significantly, they are<br>environmentally friendly: renewable, non toxic and biodegradable (Howell, 2007). In<br>summary, engine lubricants formulated from vegetable oils have the following<br>advantages deriving from their base stock<br>chemistry: higher Lubricity resulting in lower friction losses, and hence more power and<br>better fuel economy; lower volatility resulting in decreased exhaust emissions; higher<br>viscosity indices; higher shear stability; higher detergency eliminating the need for<br>detergent additives; higher dispersancy; rapid biodegradation hence decreased<br>environmental / toxicological hazards (Erhan et al., 2002).<br>In a comparison of palm oil and mineral based lubricants, palm oil based lubricants were<br>found to be more effective in reducing the hydrocarbon and carbon monoxide emission<br>levels, among other things (Masjuki et al., 1999).</p><p>23 Vegetable oils have also been identified as having a lot of potential as alternative diesel<br>engine fuels (Kayisoglu et al., 2006). This is supported by an interest in a cleaner<br>environment, as well as the increasing cost of mineral deposit based energy (Howell,<br>2007). Based on the potential availability to meet demand, soybean, peanut and<br>sunflower oils have been identified as the most promising fuel sources (Kayisoglu et al.,<br>2006). When used as a fuel, the term “biodiesel” is applicable.<br>Biodiesel is defined strictly as “…the mono alkyl ester (usually methyl ester) of<br>renewable fats and oils…” (Howell, 2007). It consists primarily of long chain fatty acid<br>esters, produced by the transesterification reaction of vegetable oils with short chain<br>alcohols. Distinct advantages of biodiesel include a high flash point of over 100oC,<br>excellent lubricity, a BTU content comparable to that of petrol diesel, and virtually no<br>sulfur or aromatic content. Above all, biodiesel is non-toxic and biodegradable (Howell,<br>2007). Results from investigating performance of vegetable oils in blends with diesel<br>indicate that blending up to 25 percent biodiesel (sunflower) with mineral diesel has no<br>adverse effect on performance (Kayisoglu et al., 2006).<br>Vegetable oils have also been applied as transformer coolant oils and have been found to<br>conform to all industry standards with performances and cost profiles comparable to the<br>conventional mineral oils applied in transformer cooling (ABB Inc., 2002). Transformer<br>oil products have been produced from soybean oils as well as castor oils (Honary, 2004).<br>Whether applied for lubrication purposes or as biodiesel or as transformer cooling fluid,<br>one of the major challenges in the utilization of the more environmentally friendly<br>vegetable oils is their poor oxidative stability (Honary, 2004), (Howell, 2007).<br>Combating the issue of oxidative instability in vegetable oils for industrial use is a<br>24 continuing research area. In the United States, for instance, three avenues are being<br>pursued. These are (Howell, 2007):<br>ï‚· Genetic modification of oils to give higher mono unsaturated compounds;<br>ï‚· Chemical modification<br>ï‚· The use of various additives and property enhancers<br>Genetic modification has been made possible by recent advances in biotechnology.<br>DuPont Technology has developed a soybean seed that presents 83% oleic acid as against<br>having the more unsaturated linolenic acid as the major constituent. This new seed<br>provides oils that show about 30 times the oxidative stability and viscosity stability of the<br>conventional oil. High oleic varieties of rapeseed, canola and sunflower seed oils are<br>increasingly being used as base stocks for lubricant formations (Honary, 2004).<br>Chemical modifications involve the partial hydrogenation of the vegetable oil and a<br>shifting of its fatty acids (Honary, 2004). In one study, epoxidized soybean oil was<br>chemically modified with various alcohols in the presence of sulfuric acid as a catalyst.<br>Better performance was recorded (Hwang et al., 2001).<br>The use of additives known as antioxidants to control the development of oxidative<br>rancidity has been applied in the US since 1947 (Bennion, 1995). They still remain one of<br>the most efficient and cost effective ways to improve the oxidative stability of oils in both<br>domestic and industrial conditions.</p> <br><p></p>