2.0 CHAPTER TWO: REVIEW OF RELATED LITERATURE2.1 OVERVIEWPalm oil is an edible vegetable oil derived from the mesocarp of the fruit of the African oil palm known as Elaeis guineensis (Reeves et al, 1979). A naturally reddish oil owed to high content of beta-carotene.Palm oil is a highly saturated vegetable fat and is semisolid at room temperature (Behrman et al, 2005). A low cost commercial and domestic food commodity worldwide especially in Africa, South East Asia and Brazil (2006).It has high oxidative stability when refined and the refined product is used for frying (Cheman et al, 1999) and (Matthias et al, 2007).It is reported that humans consume and average of 17 pounds (7.7kg) of palm oil per person (Raghu et al, 2017) in the German alps, palm oil is used to make milk substitutes that are used to make milk to feed calves in dairies (DW Germany, 2017).2.1.2 COMPOSITIONPalm oil is made up of fatty acids esterified with glycerol and has a high concentration of saturated fat especially the 16-C saturate fatty acid.Other components of palm oil are the monosaturated oleic acid and tocotrienol (Ahsun et al 2015) and (Oiming et al Ed. 2015).According to Anderson, 2007 palm oil is composed of 57% saturated, 39% monounsaturated and 10% polyunsaturated.The approximate concentration of esterified fatty acid in palm oil is as given below (2014).ACIDSTATEPERCENTAGECARBONMyristicSaturated114PalmiticSaturated43.516StearicSaturated4.318OleicMonounsaturated36.618LinoleicPolyunsaturated9.118.5Others-5.5-TABLE 2.1According to McCance, 1991 and Altar, 2006; palm oil is composed of 45.3 g/100g Saturated Acid; 41.6 g/100g Monounsaturated Acid; 8.3 g/100g Polyunsaturated Acid and 33.12mg/100g Vitamin E. 2.1.3 SATURATED VS UNSATURATEDAccording to Dr. Anne Vanbebar saturated fats are solid at room temperature because they have no double bond between molecules, meaning they have no gaps and the fat is saturated with hydrogen molecules.Whereas, unsaturated fats are liquid at room temperature because they have double bonds which breakup the chain of hydrogen molecules and create gaps allowing the fats to liquefy.An unsaturated fat is a fat in which there is at least one double bond within the fatty acid chain. A fatty acid chain is monounsaturated if it contain one double bond and polyunsaturated if it contains more than one double bond.Where a double bond is formed, a hydrogen atom is subtracted from the carbon chain. Thus a saturated fat has no double bonds and has the maximum number of hydrogen bonded to the carbons and therefore is saturated with the hydrogen atoms.In cellular metabolism, unsaturated fat molecules contain somewhat less energy (i.e. fever calories) than an equivalent amount of saturated fat. The greater the degree of unsaturation in a fatty acid (i.e. the more double bonds in the fatty acid) the more vulnerable it is to lipid peroxidation (rancidity). Antioxidants can protect unsaturated fat from lipid peroxidation.Double bonds may be in either a Cis or a Trans isomer depending on the geometry of the double bond. In the Cis isomer, hydrogen atoms are on the same side of the double bond; whereas in the Trans isomer, they are on opposite sides of the double bond.Saturated fats are useful in processed foods because they are less vulnerable to rancidity and usually more solid at room temperature than unsaturated fats. Unsaturated chains have a lower meeting point, hence these molecules increase the fluidity of cell membranes.Although both monounsaturated and polyunsaturated fats can replace saturated fat in the diet Trans unsaturated fats should not. Replacing saturated fats with unsaturated fats helps lower the level of total cholesterol and LDL cholesterol in the blood (Reiner, 2011).Trans unsaturated fats are an exception because the double bond stereochemistry predisposes the carbon chains to assume a linear conformation, which conforms to rigid packing as in plague formation. The geometry of the Cis double bond induces a send in the molecule, thereby precluding rigid formation. Natural sources of fatty acids are rich in the Cis isomer.Although polyunsaturated fats are protective against cardiac anhythmias, a study of post-menopause women with a relatively low fat intake showed that polyunsaturated fat is positively associated with progression of coronary atherosclerosis, whereas monounsaturated fat is not, (Darush et al 2004). This probably is an indication of the greater vulnerability of polyunsaturated fats to lipid peroxidation against which Vitamin E has been shown to be protective (Leibovitz et al, 1990).Although unsaturated fats are conventionally regarded as healthier than saturated fats (BBC, 2013) the United States food and drug administration (FDA) recommendation states that the amount of unsaturated fat consumed should not exceed 30% of one’s daily caloric intake.In chemical analysis, fatty acids are separated by gas chromatography of methyl esters, additionally, a separation of unsaturated isomers is possible by augmentation thin-layer chromatography (Brever et al, 1987).22.214.171.124 MONOUNSATURATED VS POLYUNSATURATEDUnsaturated fats are collectively referred to as healthy fats because they do not appear to promote the formation of atherosclerosis, a waxy plague that can build up in the human blood vessel. It exists in two forms, monounsaturated and polyunsaturated.The monounsaturated fats have only one double bond in their molecular structure, whereas the polyunsaturated differ in that they have more than one double bond in their structure (Moll & Fogoros, 2017).2.2 LINOLEIC ACIDIn Cyberlipid (an online source), Linoleic Acid is defined as a carboxylic acid, a polyunsaturated omega -6 fatty acid, an 18 carbon chain with two double bonds in cis configuration. Having a shorthand notation like “18:2 (n-6)” or 18:2 cis-9, 12″ and naturally as a triglyceride ester because free fatty acids are generally low in foods (ncbi.com).According to the International Units for Pure and Applied Chemist (IUPAC) Linoleic Acid is named as (92,122)-9, 12-octa decadienoic acid with a chemical formula C18H32O2.Linoleic Acid is a colourless oil with density of 0.9g/cm3 and melting point ranging between -5oC and 12oC. It is soluble in water (0.139mg/dm3) boiling at 230oC with a flash point of 112oC (GESTIS).Linoleic acid belongs to one of the two families of essential fatty acids (Bur, 1930) which mean that the human body cannot synthesis it from other food component.As an essential fatty acid, Linoleic Acid must be consumed by humans for proper health. A diet deficient in linoleate being the salt form of the acid causes mild skin scaling, (Cunnane, 1997) and poor wound healing in rats (Futting, 1999).Amazingly, a dead cockroach releases linoleic acid which prevents other roaches from coming close. A similar mechanism displayed by ants and bees who release Oleic Acid upon death. (Earth News).2.2.1 USES OF LINOLEIC ACID126.96.36.199 INDUSTRIALLYLinoleic Acid is used in making quick drying oils, which are useful in oil paints and varnishes. An application exploiting rancidity which is the easy reaction of the acid with oxygen in air and leading to a cross linking and formation of a stable film called linoxyn.Reduction of linoleic aids yields linolyl alcohol because linoleic acid is a surfactant with a critical micelle concentration of 1.5 x 10-4 M @ PH 7.5.Linoleic acid has become increasingly popular in the beauty products industry because of its beneficial properties on the skin. Research points to linoleic acid’s anti-inflamatory, acne reductive, skin lightening and moisture retentive properties when applied topically on the skin.188.8.131.52 IN RESEARCHLinoleic acid lipid radicals can be used to show the antioxidant effect of polyphenols and natural phenols. Experiments on linoleic acid subjected to 2, 2′ – Azobis (2-amidino propane) dihydrochloride induced oxidation of linoleic acid; hence producing lipid radicals and then the use of different combination of phenolic show the binary mixture can lead to either a synergetic antioxidants effect or to antagonistic effect towards the lipid radicals.Research like this is useful in discovering which phenols prevent rancidity also being the autoxidation of lipids in vegetable oils (Peyrat et al 2003).184.108.40.206 IN PHYSIOLOGYLinoleic Acid is used in the biosynthesis of Arachidonic acid, prostaglandins lenkotrienes and thromboxane. It is abundant in many nuts, fatty seeds and their derived vegetable oils (2007).2.3 ESSENTIAL FATTY ACIDSThese are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them. (Robert 1980).Only two fatty acids are known to be essential for humans:- Alpha – linolenic acid, an omega 3 fatty acid- Linoleic acid, an omega 6 fatty acid (Whiney, 2008);when the two EFA’s were discovered in 1923, they were designated Vitamin F but in 1929 research on rats showed that they were both better classified as fats rather than vitamins (Burr et al 1930).2.3.1 FUNCTIONSTo humans, essential fatty acid serve multiple functions. A balance between dietary Omega 3 and Omega 6 strongly affects functions;they are modified to make;the classic eicosanoids which affect inflammation and many other cellular functions.the endo cannabinoids which affect mood, behavior and inflammation.the lipoxins which are a group of eicosanoid derivatives formed via the lipoxygenase pathway from omega 6 EFA’s and resolving from Omega 3 in the presence of acetyl salicylic acid, down regulating inflation.the isofurans, neurofans , isoprotanes, hepoxilins , epoxy eicosatrienoic acids and neuro protectin D.they form lipid rafts effecting cellular signaling (Stillwedl et al 2005).They act on DNA – activity or inhibiting transcription factors such as NF-WB which is linked to pro-inflammatory cytokine production (Calder 2004).Collins et al 1970 were the first to demonstrate linoleic acid deficiency in adults, they found that patients undergoing intravenous nutrition with glucose become isolated from their fat supplies and rapidly developed biochemical signs of essential fatty acid deficiency and skin symptoms.2.4 FATTY ACID In chemistry, especially Biochemistry, a fatty acid is a carboxylic acid with a long aliphatic chain, which is either saturated or unsaturated.Most naturally occurring fatty acids have an unbranched chain or an even member of carbon atoms from 4 to 18 (IUPAC, 1997).Fatty acids are usually derived from highly carbides or phospholipids. Fatty acids are important dietary sources of fuel for animals because, when metabolized, the yield large quantities of Adenosine triphosphate (ATP). Many cell types can use either glucose of fatty acids for this purpose.Long chain fatty acids cannot cross the Blood Brain Barrier (BBB) and so cannot be used as fuel by the cells of the central nervous system. However, free short chain fatty acids and medium chain fatty acids can cross the BBB (Tsuji, 2005) and (Vijay, 2014) in addition to glucose and ketone bodies.The concept of fatty acid (acide gras) was introduced by Mihchel Eugene Chevieul, though he used initially some variant terms, graisse acide and acide huileux (acid fat and oily acid) (Menten).Chemical structure of linoleic acidCH3 (CH2)4CH = CHCH2 CH = CH (CH2)7 COOH2.4.1 LENGTH OF FREE FATTY ACID CHAINSFatty acid chains differ by length, often categorized as short to very Cory.1. Short chain fatty acids (SCFA) are fatty acid with aliphatic tails of five or fewer carbons (Cifuentes, 2013).2. Medium chain fatty acids (MCFN) are fatty acids with aliphatic tails of 6 to 12 carbons (Roth, 2013) which can form medium chain triglycerides.3. Long chain fatty acids (LCF) are fatty acids with aliphatic tails of 13 to 21 carbons (Beermann, 2003).4. Very long chain fatty acids (VLCFA) are fatty acids with aliphatic tails of 22 or more carbons.2.4.2 INDUSTRIAL PRODUCTIONFatty acids are usually produced industrially by the hydrolysis of triglycerides with the removal of glycerol. Phospholipids represent another source. Some fatty acids are produced synthetically by hydrocarboxylation of alkenes.2.4.3 BY ANIMALS Fatty acids are formed from carbohydrates predominantly in the liver, adipose tissue, and the mammary glands during lactation (Shyer, 1995).Carbohydrates are converted into pyruvate by glycolysis as the first important step in the conversion of carbohydrates into fatty acids (Shyer, 1995).Pyruvate is then dehydrogenated to form acetyl-CoA in the mitochondrion. However, this acetyl CoA needs to be transported into cytosol where the synthesis is of fatty acids occurs. This cannot occur directly. To obtain cytosolic acetyl-CoA, citrate (produced by the condensation of acetyl-CoA with Oxaloacetate) is removed from the citric acid cycle and carried across the inner mitochondrial membrane into the cytosol. (Shyer 1995). There it is cleaved by ATP citrate lyase into acetyl –COA and oxaloacetate. The oxaloacctate is returned to the mitochondrion as malate (Ferre & Foufelle, 2007).The cytosolic acetyl- CoA is carboxylated by acrytyl-CoA carboxylase into malonyl-CoA, the first committed step in the synthesis of fatty acids (Ferre & Foufelle, 2007) and (Voet et al 2006).Malonyl-CoA is then involved in a repeating series of reactions that lengthen the growing fatty acid chain by two carbons at a time.Almost all natural fatty acids, therefore have even members of carbon atoms. When synthesis is completed, the free fatty acids are nearly always combined with glycerol (3 fatty acids to one glycerol molecule) to form triglycerides, the main storage form of fatty acids and thus of energy in animals.However, fatty acids are also important components of the phospholipids that form the phospholipid bilayers out of which all the membranes of the cell are constructed (the cell wall, and the membranes that enclose all the organelles within the cell, such as the nucleus, the mitochondria, endoplasmic reticulum, and the Golgi apparatus.) (Shyer, 1995).The uncombined fatty acids or free fatty acids found in the circulation of animals come from the breakdown (or lipolysis) of stored triglycerides (Shyer, 1995) and (Zechner et al 2005).Because they are insoluble in water, these fatty acids are transported bound to plasma albinum. The levels of free fatty acids in the blood are limited by the viability of albinum binding sites. They can be taken up from the blood by all cells that have into mitochondria (with the exception of the cells of the central nervous system).Fatty acid a can only be broken down to CO2 and water in mitochondria by means of beta-oxidation, followed by further combustion in the citric acid cycle. Cells in the central nervous possess mitochondria cannot take free fatty acids up the blood, as the BBB is impervious to most free fatty acids excluding short claimed fatty acids and medium chain fatty acids (Vijay, 2014, Tsuyi, 2005).These cells have to manufacture their own fatty acids from carbohydrates, as described above, in order to produce and mountain the phospholipids of their cell membrane and these of their organelles (Styer, 1995).2.5 OMEGA 6 FATTY ACIDAlso referred to as 10 – 6 or n – 6 fatty acids are a family of pro-inflammatory and anti-inflammatory and anti-inflammatory polyunsaturated fatty acids (Nowak, 2010) that have in common a final carbon-carbon double bond counting from the methyl end (Chow, 2001).Their biological effects are largely produced during and after physical activity for the purpose of promoting growth and during the inflammatory cascade to halt cell damage and promote cell repair by their conversation to omega- 6 eicosanoids that bind to diverse receptors found in every tissue of the human body.2.6 TRIGLYCERIDE`A triglyceride also known as TG, triacylglycerol, TAG or triglyceride is an ester derived from glycerol and three fatty acids (from tri-and glyceride) (IUPAC 2007).Triglycerides are the main constituents of body fat in humans and other animals, as well as vegetable fat (Nelson & Cot, 2000).They are also present in the blood to enable the bidirectional transference of adipose fat and blood glucose from the liver and are a major component of human skin oils (Lampe et al 1983).There are many different types of triglyceride, with the main division between saturated and unsaturated types. Saturated fats are “saturated” with hydrogen-all available places where hydrogen atoms could be bonded to carbon atoms are occupied. These have a normal melting point and are more likely to be solid at room temperature. Unsaturated fats have double bonds between some of the carbon atoms. These have a lower melting point and are more likely to liquid at room temperature.Most natural fats contain a complex mixture of individual triglycerides. Because of this, they melt over a broad range of temperatures. However, cocoa butter is unusual in that it is composed of only a few triglycerides, derived from palmitic, oleic, and stearic acids in the 1-,2-, and 3-positions of glycerol, respectively (Alfred, 2002).2.7 HOMOTRIGLYCERIDESThe simplest triglycerides are those where the three fatty acids are identical. Their names indicate the fatty acids: stearin derived from stearic acid, palmitin derived from palmitic acid, etc. These compounds can be obtained as three forms or polymorphs: ?, ?, and ?’: these forms differ terms of their melting point (Alfred, 2002 and Cherbonnet, 1947).2.8 CHIRALITYIf the first and third chain R and R” are different, then the central carbon atom is a chiral center, and as a result the triglyceride is chiral. (Lok, 1976).In human body high levels of triglycerides in the blood stream have been linked to atheros clerosis and, by extension, the risk of heart disease (Boston globe, 2014) and stroke (Drummond, 2014). However, the relative negative impact of levels of triglyceride compared to that of LDL: HDL ratios is as yet unknown. The risk can be partly accounted for by a strong universe relationship between triglyceride level and HDL cholesterol level.2.9 PHOSPHOLIPIDSPhospholipids are a class of lipids that are a major component of all cell membranes. They can form lipids bilayers because of their amphiphilic characteristics. The structure of the phospholipid molecule generally consists of two hydrophobic fatty acid “tails” and a hydrophilic “head” consisting of a phosphate group.The two components are joined together by a glycerol molecule. The phosphate groups can be modified with simple organic molecules such as choline.The first phospholipid identified in 1847 as such in biological tissues was lecithin, or phosphatidylcholine, in the egg yolk of chickens by the French chemist and pharmacist, Theodore Nicolas Gobley.Biological membranes in eukaryotes also contain another class of lipid, sterol interspersed among the phospholipids and together they provide membrane fluidity and mechanical strength.Purified phospholipids are produced commercially and have found applications in nanotechnology and material science (Mashagi, 2013).