PALM KERNEL OIL LITERATURE REVIEW - HISTORY, EXTRACTION, USES, CLASSIFICATION ,COMPOSITION, PROPERTIES

CHAPTER TWO
LITERATURE REVIEW
1.1             Historical Development of Palm Kernel Oil
            The development of oil palm (Elacis guineensis) starts about 2 week after an thesis (WAA); at 8WAA the endosperm of the seed is liquid and at 10 WAA, it is semi gelatinous (Hartley el al, 1998): At 12 WAA oil start to deposit in the endosperm and almost complete by 16WAA. During this period the endosperm and endocarp slowly harden and by 16WAA the endocarp is hard shell enclosing a hard whitish endosperm which is known as kernel, (Oo et al, 1985), Sambanthamurthi et al, 2000). Oil deposit in the Mesocarp start at about 15WAA and continues until fruit maturity (about 20 WAA, Bafor and Osangie, 1986). Oo et al (1985), also observed that as the total lipid progressively increases (0.1-48%) in the Mesocarp the Moisture Content decreases (88-37%) with increasing WAA.

            The tree is generally believed to have originated in the jungle forests of East Africa and there is some evidence that palm oil was used in Egypt at the time of the pharaohs, some 5000 years age (Cottrel, 1991) but now its cultivation is mostly in South East Asia. There are three main varieties of oil palm distinguished by their fruit characteristics. These are.
            Dura, which has a think shell separating the pulp from the Kernel. The tends to be large comprising 7%-20% fruit weight.


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            Tenera, which has a think shell between pulp and kernel, together with a fibrous large round the nut. The kernel, together with a fibrous large the nut. The kernel is usually smaller comprising of 3%-15% of fruit. The oil content is higher at 24%-32%.
            Pisifera, which has no shell and is very frequently female sterile, as a result of their very market tendency to female sterility, Pisifera palm are not used for commercial planting.
            In general all crude palm oil extracting method includes a sterilization process where the fruit is softened up usually by heat treatment, and a digesting stage where there pulp is broken up to release the oil an extraction process to release oil from mashed fruit and a purification and clarification process where the oil is separated from water and cell debris (slugde), fiber and shell. Further downstream kernel obtained often the oil extraction process is separated from the fiber, cracked and sold or subjected to palm kernel oil extraction. The expert of palm kernel began in 1832 and by 1916 British West Africa alone exported 156,000 tones of which about 75% from Nigeria (Smith 2009), Nigeria was the largest exporter until 1934 when the country was surpassed by Malaysia Crest Africa let the world in the production and export of palm oil throughout the first half of the 20th century, led by Nigeria and Zaire. By 1995, however, Malaysia and Indonesia has surpassed African’s total palm oil production (Smith, 2009).
            The palm fruit looks like a plum, the outer flesh mesocarp gives the oil palm, while he kernel which is inside a hard shell give the palm kernel oil, and its rather strange that the two oil from the same fruit are entirely different in fatty acid composition and properties (Smith 2009).    The palm kernel oil is light yellowish fatty oil obtained especially from crushed nuts of an African palm. It is composed of fatty acids, esterifies with glycerol just like any Ordinary fat (it is a triacyglycerol). The oil gotten from the kernel by extraction is usually colorless or pale yellow. The oil is more liquid than palm oil hence, it is composed of mainly unsaturated fatty acid primary lauric (Ihekeronye and Ngoddy 1985). The residue left after extracting oil from the kernel usually are referred to as palm kernel cake is used in the manufacture of livestock feed.

2.2       Palm Kernel Oil and its Composition
            Composition of Palm Kernel Oil          
            Palm kernel oil is less healthy than palm oil which is derived from the flesh of the fruit itself palm kernel oil is over 80 percent fat content. 48 percent of this fat is made up of lauric acid, with myristic and Oleic acid making up another 30 percent of its fatty acid composition. It is because of this composition that palm kernel oil is had at room temperature and has a low melting point (Cottrel 1998). Palm kernel oil (triglyceride) like other nature fats and oils is a chemical compound of one molecule of glycerol, bound to three molecules of fatty acids.
CH2 – OH + R – COOHCH2 – COOR
CH2 – OH + R – COOHCH – COOR + 3H2O
CH2 – OH + R – COOHCH2 – COOR
            Glycerol         fatty acid                   water   
            Triglyceride is the major form of lipid in the body an food. It is composed of fatty acids, esterifies with glycerol that is glycerol’s with three fatty acids (triacyglycerol) attached to the ester.            Triglyceride molecules contain a “Back bone” of three carbon alcohol (glycerol). A fatty acid is attached to each of the three hydroxyl (OH), of glycerol. The molecules of water is released in the process of bonding three fatty acid to glycerol as shown above. The degree of saturation and the chain length of the fatty acids in the triglycerides found in food are important determinant of the properties of oil. The shorten chain fatty acid are of lower melting point and are more soluble in water (Wolfong and Salmiab, 2007).

Table 1: Fatty Acid Composition of Palm Kernel Oil (2002)
Palm Kernel Oil
Fatty Acid
48%
Lauric acid (12.0)
16%
Myristic acid (14:0)
8%
Palmitic acid (16:0)
2%
Stearic acid (18:0)
15%
Oleiv acid (18:1)
3%
Linoleic acid (18:2)

            The heavy content of lauric acid gives palm kernel oil its sharp melting properties meaning hardness at room temperature combined with low melting point (Pantzaria, 2000). In the presence of heat and water, the triglyceride (vegetable oil) break down by a process known as hydrolysis to form raw fatty acids and glycerol.
Fats/Oil + H20 + catalyst fatty acid + glycerol
                                         Heat  
            Palm kernel oil can be fractionated into solid and liquid fractions known as stearin and Olein respectively and then go for refining to give refined bleached deodorized (RBD) (Pantzaris, 2000) which is of crucial important to refiners. Moisture and dirt composition of palm kernel oil can be reduced by good milling and extraction but normally it is in the range of 0.25%
Other Moisture contents are: 
Ø    The Carotenoids /Antioxidants
Ø    The tocopherols / vitamins
Ø    The sterols (e.g cholesterol)
Ø    The polar lipids
Ø    The phospholipids
Ø    Hydrocarbons
Ø    Other impurities
All the classified in one category because they are fatty in nature but not really oils. They are referred to as unsaponificable matter. These unsaponificable matters are defined as material left behind the oil and fat which after saponification of the oil or fat by caustic alkali and extraction by a suitable solvent, remains non-volatile on drying at 80C (Loh 2010).Removal of these impurities is by degumming of the oil. Degumming of palm kernel oil is a process equally known as water refining. This consists of treating the nature oil with small water, followed by centrifugal separation. This is aimed at removing the gummy or waxy solid are dissolve in the oil (soluble organic matter) the essence of degumming is purification i.e to purify the oil (Sivasothy et al 1986).

2.3       Production of Palm Kernel Oil
2.3.1   Solvent Extraction of Palm Kernel Oil
            Solvent extraction processes can be divided into three main unit operations: Kernel pretreatment, oil extraction, and solvent recovery from the oil and meal. For the purposes of small operations it is sufficient to mention the solvent extraction process is an alternative for high capacity mills. However, the process is not recommended for small enterprises. (Sivasothy’s 2006).

2.3.2   Traditional Method of Palm kernel Extraction
            Palm kernel extraction is a specialized operation undertaken by a completely different set of processors. They are usually better organized as a group and are not as dispersed as palm oil processors. The kernel processors have to go around the palm oil processors during the peak season, when prices are lowest, to purchase the nuts for drying. The nut processing and oil extraction is undertaken in the day season. When the pressure to obtain raw materials has subsided (Belge, 1955), The traditional palm oil processing starts with the shelling of the palm oil nuts. The shelling used to be performed using two stones to crack each nut and separating the kernel and shell simultaneously. This manual operation has been largely superseded by the use of nut-cracking stations (Malaysia palm oil Boad, Kuala Lumpu 1986).         The mechanical nut-crackers deliver a mixture of kernels and shell that must be separated. The kernel/shell separation is usually performed in a day-bath, which is a concentrated viscous mixture of clay and water. Th5e density of the clay-bath is such that the shells sink while the lighter kernels float to the top of the mixture. The floating kernels are scooped in baskets, washed with clean water and dried. Periodically, the shells are scooped nut of the bath and discarded.
            The traditional oil extraction method is to fry palm kernels in old oil or simple heat and the dried nuts. The fried kernels are then pounded or ground to a paste in a motorized grinder. The paste is mixed with a small quantity of water and heated to released the palm kernel oil. The released oil is periodically skimmed from the top. The Today, there are stations in villages that will accept well-dried kernels for direct extraction of the oil in mechanized, motorized expellers (Khairah, 2006).

2.4       Uses of Palm Kernel Oil
2.4.1   Food Uses of Palm Kernel Oil
Processed foods in which trans fat have been replaced are often replaced with palm kernel oil. Product like Margarine caramel, ice cream, vegetable shortening, powered milk and milk whiteners are where palm kernel oil is most often found. These processed food are high in saturated fat and many health experts advise consumers to stay away from such foods.

Hydrogenated Palm Kernel Oil
            When palm kernel oil is hydrogenated. It can be blended with other high-fat oils and used for very specific food applications, especially those in which “Mouth feel” is important, because it produces a non-greasy sensation on the tongue. Hydrogenated palm kernel oil is more stable and can withstand being softened without melting, making it ideal for use in foods such as chocolate candy bars and margarine, (Podczasy et al, 1994).

2.4.2   Non-Food Uses of Palm Kernel Oil
            Though palm kernel oil is used primarily in foods, it is also converted into biodiesel as an alternative to traditional oil, and is found in soaps or other cleaning agents, palm kernel oil is prized as a soap lauric acid. It lathers well and lends a firmness to soap that are otherwise too soft to hold their shape, (Cornelius 1997).

2.5       Classification of the Palm Kernel Oil
            What is the difference between palm oil and kernel oil? The specific fatty acid were provided as current research suggests that they cannot simple classify all saturated fat as being “bad”. What are saturated fats, the scientific definition on saturated fat is having every carbon bound to as many hydrogen’s are possible, absence of double bounds, saturated fat and saturated fatty acids may be used interchangeable. Often saturated fatty acids, the length of the carbon chain differentiate saturated fatty acids. The saturated fatty acids commonly found in a typical American diet are lauric acid, myristic acid, palnutic acid, and stearil acid. As a ruler of thumb, the great saturated fat in a food item, the more solid it will be at room temperature. The reverse is also true, the greater the unsaturated fat in a food item, the more liquid  it will be at room temperature (Katan, M.B. et al 1994). There is scientific evidence that not all saturated fats are equally cholesterol elevating. Studies have found that, compared to other long chain saturated fatty acids stearic acid appears to have a neutral effect on total cholesterol; and low-density lipoprotein (LDL) otherwise known as the “bad” cholesterol, studies have found that compared to palmitic acid, lauric acid and myristic acid increase total blood cholesterol (the “bad” cholesterol) high density lipoprotein (HDL) the “good” cholesterol, and the LDL/HDL ratio in both non human primates, and normo-cholesterolemic men and women who consumed a typical western diet. The myristic acid and lauric acid from coconut oil increased total blood cholesterol, LDL, HDL and triglycerides (Etherton et al, 1995). Another study found that in normo-cholesterolemic palmitic acid and oleic acid produced similar effects on LDL and HDL metabolism. The finding were confirmed in studies with normolipidemic humans who consumed a moderate fat diet low in myristic acid and dietary cholesterol, which found the effect of palmitic acid on total blood cholesterol and LDL/HDL ratio to be comparable to that of Oleic acid. Oleic acid is a mono unsaturated fatty on total blood cholesterol, LDL and HDL, in comparism with saturated fats (Diersen-Schade 1991).
            In summary, the literature suggests that both stearic acid and palmitic acid, which comprise virtually all the saturated fats in palm oil have neutral to favorable impact on serum lipid profits compared to lauric and myristic effect of dietary stearic acid on plasma cholesterol and lipoprotein level. N. Engl J. Med. 318: 1244-1248. (Bonanome, & Grundy, 1988). The majority of unsaturated fat molecules are in the cid configuration thus having the carbons on the same side of the double bond. Most unsaturated fats are Cis except for some naturally occurring trains in meats and milk. However, when hydrogenation, taking a liquid fat and making into a solid fat by the addition of hydrogen’s, is performed trans fats are created; trans fats have the carbons on the opposite side of the double bond. hydrogenation is used to remove the instauration of fatty acids in order to increase the oxidative stability of oils and to raise their physical properties allowing for a broader range of usage in the food industry. Hydrogenated oils are often used in processed food due to their stability. Trans fats have not been required on the food label, but will be as of 2006, A product contains trans fatty acids if a hydrogenated oil is listed under the “ingredient” section of the food label. Research has shown a detrimental effect of trans fat on cholesterol (see which is better trans fat or saturated fats), (Sunkin et al, 1994). Extensive research on trans fats has occurred in the past decade. Numerous studies have suggested that trans fat consumption elevates low density lipoprotein (LDL) cholesterol (the “bad” cholesterol) 1,2,3,4,5 and decreases the ratio of high density lipoprotein resulting in a less desirable cholesterol profit 6 in 1999, a meta-analysis of comparative effects of trans fats versus saturated fats on cholesterol was performed. This study found that as the fat intake increase the LDL: HDL cholesterol ratio (a low value is desired) also increased in a dose-dependent manner, and that trans fat consumption increased this ration by more than saturated fat consumption (Mutanen et al, 1997).
            Tropical oils are generally though of as having a high saturated fat content and should be avoided. Although, palm oil is grown in the tropical region compare to other tropical oils, its saturated fat content is approximately 30% less. Palm oil is often confused with the more highly saturated palm kernel oil and coconut. Studies have found that, unlike coconut oil, palm oil’s impact on serum lipid and lipoprotein profiles compares favorably to corn oil, hydrogenated soybean oil, and olive oil. A 1995 study company the effect of palm Olein and Olive Oil diets on twenty-one healthy, free-living normo cholesterolemic subjects found no difference in total and low density lipoprotein (LDL) cholesterol levels. In sum, palm oil appears to affect serum lipids more like a monounsaturated than a saturate oil (Truswell, 1995).

2.5.1   Palm Acid Oil (PAO)
            Palm Acid Oil (PAO) is a by-product from the chemical refining of palm oil. It consist mainly of FFA over (50% and neutral oil, with 2-3% moisture and other impurities. It is very similar to palm acid distillate (PFAD), but its FFA is generally lower, except for some special uses, the relative proportion of FFA to neutral oil does not usually mater very much, as it does not affect its fitness for use. In most cases the smell and colour are more importance. The main uses of PAO are in animal feed in soap making and for distilled fatty acid production. This product is not now produce on any great scale outside Europe, because in Malaysia and Indonesia palm oil is refined by the physical process which gives (PFAD) rather than PAO (Ataga et al, 1993).

2.5.2   Palm Fatty Acid Distilled (PFAD)
            Palm fatty acid distilled (PFAD) is a by-product from the physical refining of palm oil which is now the most widely used process in the major producing countries. Its scale of production is large enough to support significant international trade in it. (PFAD) has very similar composition to palm acid oil (PAO) but it generally has higher FFA (over 70%), the balance being neutral oil and up to 1% moisture and impurities (Koh et al 1981). Good qualities material has good smell and high colour its main uses are in animal feeds, including some speciality products, in soap making and in the product of distilled fatty acids. This product is produced in much greater volume than PAO.

2.5.3   Palm Kernel Oil (PKO)                                          
            Palm kernel oil (PKO) is derived from the kernel of the palm fruit and so it is a co-product of palm oil production, Linoleic acid (12%). However, refined blenched deodorized (RBD) palm oleic oil POo­­ is usually traded on the specification of FFA 0.1% max SMP 24C Max and IV56min (Smith et al 1986) on loading. There is a good inverse correlation between the IV and the SMP and SFC of Oleic, and buyers should aim for the highest Value POo is much more stable to Oxidation and flavour deterioration than any of the major seed oils, its main disadvantage being its tendency to become cloudy, or even semi-solid in temperature climate.

2.5.4   Palm Steaerin (Ps or PO­s)
            Palm stearin is the harder fraction from the fractionation of palm oil, the softer fraction being the Olein. The name stearin is usually abbreviated as POs or Ps, with the fish one more usually in technical writings. The demand for stearin is lower than that for olein and so it has always been sold at discount to both Olein Oil. The main characteristics of POs and SMP 47-54, IV 28 45 and SFC 25-71% at 20c its average fatty acid composition is palmitic acid (57%). Olein acid (20%) and linolein acid (7%), (Atage et al 1998). However, refined blenched deodorized (RBD) POs is usually traded on the PORAM specification of FFA 0.2% Max, SMP 44c Min. and IV48 Max on loading. In the past, there was much futile debate whether oils of such high melting would have reduce digestibility and indeed whether they could be considered edible. POs is ment to be blenched with other softer oils and it is the MP of the blend that counts and nut that of its components. Palm stearin is very useful in the formulation of pastry margarine, table margarine with interesterification and of hard long lasting soap.

2.5.5   Double Fractionated Palm Olein or Super Olein (PO­oo or DFPO)
            Double fractionated palm Olein, or Super Olein is a softer typer of Olein Obtained by fractionation of the standard Olein in order to achieve the maximum possible fluidity. The name is POoo or DFPOo the first one more usual in technical writing writings. This is a speciality product, for which there is no common standard such as PORAM, and so there are difference according to manufacturer. Its price is always at a premium to standard Olein. The main characteristic of POoo are SMP 13-17c IV 60-68 and SFC 0-26% at 10c. Its major fatty acids are palmitic acid (35%), Olein acid (45%) and linolein acid (13%) (Ataga et al,1998). different manufacturer set their own Limits within the above ranges POoo is used for bottling, as it remains fully liquid in tropical climates and also in temperate climates if blended with sufficient seed oil. Its great advantage over the major seed oils is its much grater resistance to oxidation.
            But palm kernel oil (PKO) is the minor product and in World terms, about 8½ tones PO is produced for every tonne of PKO. This oil together with coconut oil compose the lautic group. So named because their fatty acid composition is based predominately on lauric acid PKO has a slip melting point of 26-28c, iodine value 16-19 and SFC (20c) about 40%. Its fatty acid composition consist mainly of lauric acid (c 12:0) about 48%, myristic and (C 14;0) 16% and Olein acid (18:0) 15%, with total saturates of about 82% crude PKO is usually traded on the basis of FFA 5% max. Moisture and impurities 1% max and IV 19 max (Ataga et al 1998), on loading. Palm kernel oil (PKO) is very similar to coconut oil and has very similar uses, primarily in ice cream, sugar confectionary, substitute chocolate, special bakely margarines Oleochemical and soap. A proportion of lauric oil is necessary in soap formulations, to confer good latering properties PKO is also fractionated into PK stealin (used as CBS) PK Olein.

2.5.6   Palm Kernel Stearin (PKS)
            As in the case of palm oil (PO) substantial quantities of palm kernel oil (PKO) are fractionated in the producing countries and in Europe, into PKS and palm kernel Olein (PKOo), but in this case the stealin is the more valuable product, compared with PKO, it has higher melting point, lower IV and higher SFC at all temperatures. Typical values are SMP 32-33c, IV 6-8, SFC (20) about 82% and SFC (35) 0%. The lauric acid (C 12:0), content is about 57% (Lumpur et al 1996). The combination of very high SFC (20), low MP and good Oxidative stability, makes PKS excellent confectionery fat. It main use is as a coca butter substitute (CBS) either as it stands or after some hydrogenation. It is also used for other confectionery products. High quality biscuit creams, toppings and similar products. In the past when most of its production was concentrated in west most of its production was concentrated in West Europe, this fat a rather expensive specialty. But with rapidly increasing PKO production and fractionation moving to S.E. Asia, its becoming much more easily accessible, and competitively priced.

2.5.7   Palm Kernel Olein
            Palm Kernel Olein (PKOo) is the secondary product of PKO fractionate, normally selly at a small discount to PKO. Compared with PKO the Olein has higher IV, and lower melting point and SFC at all temperature. Typical values are IV 21-25, SMP 22-25C and SFC ()20c) about 17%. Its major fatty acids are approximately lauric acid (c 12:0) 45% and Olein acid (C 18:1) 19% (Sivasothy, 2006). PKO0 is very suitable for rice cream making and also for soap production to provide the necessary lauric acid when hydrogenated PKO and can be used for the same applications such as biscuit and cake creams, sugar confectionery, chocolate flavoured coating, filled milk, coffee whiteners, vegetable cheese analogue and similar products.

2.5.8   Palm Kernel Meal (PKM)
            Palm kernel meal (PKM) is the meal left after removing the oil from palm kernel, which can be done by solvent extraction, or by pressing or both palm kernel Expellers (PKE) refer to the particular grade of meal produced using expeller-types crew processes. This grade has a higher fat content (6-86% against 1-2% for the solvent extracted meal) and no risk of residual solvent and so it is in greater demand and sells at a higher price (Koh et al 2007). PKE is the main grade imported by the EU which is its biggest importer and user. (PKM) all grades is used for animal feeds especially cattle, either alone, or after compounding with other feed to produce a more balanced food for the animal. It is classified as an energy feed and so it competes on price with copra meal, barley, corn, tapioca and similar, in contrast to Soya beans meal, fish meal etc which are “protein meals” and sell at much higher prices. PKM also has the disadvantage of higher levels of indigestible fiber and grittiness due to shell residues and afflatoxin contamination if improperly produced or shipped. PKE usually contains 14-19% protein and 6-8% fat, but in international trade the main specification item is protein + fat 21 – 23% (Alamu et al 2007).

2.6       Physicochemical Properties of Palm Kernel Oil
            Fats and oil have certain specific chemical and physical characteristics which vary within a limited range.

2.6.1   Physical Properties
1.                  Colour and Solubility: Triglycerides are hydrophobic substances that are soluble only in some organic solvents unlike many other types of complex lipids, they posses no electric charges and are therefore referred to as neutral lipid.
Palm kernel oil is insoluble in water, but when agitated with water in the presence of an             emulsifying agent, they however form an emulsion.
They are soluble in most organic solvent such as ethyl ether, chloroform, benzene, naphtha, carbon bisulphate carbon tetrachloride, etc. They are slightly soluble in alcohol. The oil is yellowish in colour depending on the processing and has a characteristics aroma of palm kernel oil due to methylyoxyketone (Esminger et al, 1990). 
2.                  Density: Densities of fats in liquid state do not differ much for most of the common fats. The density of a material is given in units cubic meter in the S.I system of units. This property is defined as the ratio of mass to volume of a substance. Generally, the mass is measured in grams and the volume in millimeters or cubic centimeters. Density measurements of liquids are straight forward and sometimes can aid in identifying pure substance mixture that contain two or three known components. They significantly in their individual densities.
3.                  Specific Gravity: Specific gravity is a related quantity that is define as the ratio of the density of the analyze to density of density of water a specific temperature. Density and specific gravity measurement rarely provide sufficient information to qualitatively identify a pure analyze. They can be used as supporting evidence, however, when an essay is performed by another procedure.
4.                  Viscosity and Oiliness: One of the most noticeable characteristics of vegetable oil is their oiliness or ability to form lubricants films. Viscosity is a measure of internal friction in molecules, the resistance of a substance to change a shape or resistance to flow of a liquid. This is measured by viscometer. The higher the flow rate, the lower the viscosity. The rate is expressed in centipoises. Fat and oil show relatively high viscosities  compared to other liquids because of high intermolecular attraction of the long alkyl chains of their glyceride molecules. Fat and oils behave as Newtonian liquids except at very high shear rate where degradation may begin to occur.
In general, viscosity of oil decreases slightly with increase in the degree of instauration and with increase in average molecular weight thus viscosity is increased by hydrogenation. The viscosity of oil increase markedly by polymerization, (Smith 2009). Oiliness generally connotes relative ability to operate under boundary lubrication conditions. The term relates to a lubricants tendency to wet and adhere to a surface (Knothe et al 2005). 
5.                  Melting and Solidification Point: Most mixture and amorphous solid melt over a range of temperatures. As heat is applied to a solid, its temperature will increase until the melting point is reached. More heat then will convert the solid into a liquid and the solid has melted thereby raising the temperature. Pure compounds usually display sharp melting point and impure compounds show broad melting point. Triacylceride reflect the melting point of their constituent fatty acids. A low degree of unsaturation, high molecule weight and the presence of trans rather than Cis-Isomer of unsaturated acid all contributed to a relative high melting point (Munack et al, 2007).
6.                  Refractive Index: Refractive index of a fat or oil is one of the most important acids for classifying fatty oils sense it is closely related to the nature of the product (molecular weight and degree of unsaturation) and can be determined quickly with great accuracy. In order to obtain values for both liquids and oils, most control laboratories operate the instrument at instrument at increased temperature (48-600C).
7.                  Surface and Interfacial Tension: The surface tension of refined oil such as cotton seed oils in about 35 dyn/cm and the interfacial tension against water is about 30 dyn/cm at 60-700C. Surface tension increase in chain length and decrease with increase in temperature (Schroder et al, 2001).       

2.6.2       Chemical Properties
1.         Specification value: this indicates the average molecular weight of fats and oils. The             specification             value may be defined as the number of milligrams of caustic potash             required to neutralize the fatty acids obtained by the complete hydrolysis of one gram of             oil or fat. Thus, specification value gives us information on whether.
v    An oil or fat contain lower and higher proportion of some fatty acids.
v    An oil or fat contains high proportion of lower or higher fatty acids. Since butter has a    large             proportion of lower fatty acids than lard and tallow. The former has high    specification value. Coconut oil has a comparatively high specification value (SV247), butter fat (SV225), oliver oil (SV200) and carrot oil (SV180).
1. Iodine value: iodine is a measure of the degree of unsaturation of the oil and is defined as the number of milligrams of iodine absorbed per gram of oil sample. The greater the total unsaturation, the higher the iodine value. Iodine value determination is important because depending on its value. Oil can be classified into drying, semi drying and non-drying oil. The ability of oil to undergo oxygen induced cross-link reaction leads to the formation of a solid film known as drying (kirk et al, 2009).
2. Ester value: the ester value is relative measure of the amount of ester present. It is obtained by subtracting the acid value form the specification value therefore, it is expressed in the same terms as specification value and the acid value. The process of etherification is when a fat that contains mixture of triglyceride is allowed to head in presence of an alkaline catalyst, a random exchange of acyl group takes places  between different glycerides a mixture of glyceride molecules is obtained which is quite different from the mixture of glyceride originally presents.


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