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.
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
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 DFPOo)
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.