LITERATURE
REVIEW
2.1 HISTORY OF PALM OIL:
Palm oil is oil gathered from the fruit
of oil palms, particularly the African oil palm. Oil palms are tropical plants
that are grown for their fruit and have been cultivated for centuries. The
seeds of the fruit are used for making edible vegetable oil, or palm oil. Oil
palms originated in West Africa, but have been since planted in many tropical
regions around the globe, (Berger, 1983).
Palm oil is extracted from the fruit
of the oil palm tree through a process of pressing the fruits often in an
apparatus called a screw-press. Palm oil is one of the most widely produced oil
in the world. Palm oil has become a necessity for survival of many native
populations who use the oil for fuel, cooking, heating and even lighting and
energy (Amiruddin, 1984).
2.1.1 Processing Technology
Until the early years of the twentieth
century, palm oil was processed only by traditional village methods, by which
loose fruits were collected from the ground or a few bundies were cut from the
tree. Beginning in the 1920s, however, the united Africa Company and British
colonial officials in Nigeria started experimenting with steam cookers and had
presses designed to make production at the village level more efficient in terms
of labour use and oil yield. Yet a lack of cash prevented most farmers from
trying the new machinery with the exception of a few lucky recipients of free
samples of government subsidies in the 1940s (Martin, 1988). A separate process
of trial and error led to the development of the sophisticated factories
required to deal with the volume of fruit produced on modern plantations and to
produce oil of the high and standardized quality that would appeal to Western
food processors. Such factories handle almost all the palm fruit of Southeast
Asia, whereas in West Africa and Latin America, processing is carried out by a
wide variety of methods, yielding oil for local consumption and for industrial
as well as edible uses in the West (Anwar, 1981)
2.1.2 Traditional Village Process
Whole ripe fresh fruit bunches are cut
from the palm. With the young tree this can be done from ground level, with
older tree in West Africa, harvesting is still often accomplished by a man
climbing the tree, secured to it by loop of rope or other locally available
materials, such as rattan and raffia fiber (Gapor and Berger, 1983). But on
plantations a curved knife attached to a bamboo is used. After cutting, most of
the fruits are still firmly attached to the bunches which are divided into a
few sections, heaped together, moistened and covered with leaves, natural
fermentation during two to three days loosens the fruit so that they can be
picked off the bunch sections by hand, following this step, two major variants
in the process are used to produce two oils with different characteristics,
those of soft oil and those of hard oil, (Elson 1992). But the basic methods
have changed little since they were first described by colonial officials in
the 1910s and 1920s. For soft oil production, the fruit are separated as soon
as they are loose enough and boiled with water for 4hours to soften the flesh,
which is very fibrous. The cooked fruit is emptied into a large container,
which may be a pit lined with clay, an iron drum or a large wooden mortar. It
is then reduced to a pulp with pestles or by treading it under foot. The
resulting mash may be diluted with water and the oil is skimmed of or squeezed
out of the fibrous mash by hand. In some instance, a sieve made of palm fronds
is used to retain the fibers. At this stage the liquid product which contain
oil, water and fruit fibers, is often boiled up with additional water and
skimmed again, although this step is omitted in some cases. Finally, the oil is
again heated to boil out the residual water (Heber and Ashley, 1992).
Jacobsberg (1984), observed also on
the preparation of small quantities of oil for kitchen use directly from
freshly picked fruit, boiling the fruit, pounding the fruit and skimming the
oil. Such oil had good keeping
properties and often a free fatty acid content below 2 percent but yield
was very low and not for export. In hard oil process, the fruit is allowed to
ferment for 3 or more days longer than in the soft oil process, until the flesh
is soft enough. It is then pulped by trading underfoot in an old canoe or
pounding in a mortar. Oil is allowed to drain out for 3days, then water is
added and the mix is trodden again, further oil rises to the surface and is
skimmed. The oil is boiled up with water in another container and finished as
described for soft oil. These two process differ in some important aspects such
as higher FFA, lower yield and lower labour and energy costs of the oil
produced from fruits subjected to longer fermentation time (Heber
and Ashley, 1992).
2.1.3 Mechanization of Small Scale Process
The rapid twentieth century growth in
West Africa exports brought about the introduction of simple machines to reduce
labour requirements and increase oil yield from a given quantity of fruit.
Early machine before and after the 1914-18 war, as described by Hertley (1988),
included a cylinder fitted with manually operated beaters, which was fed with
softened fruit and hot water. After beating the palm fruit, water mixture was
run off through a sieve. Another system used a special cooker and a press as
adjuncts to the soft-oil process. The first device to become widely adopted,
however was a modified wining and cider press, the Duchscher press
(Cottrel,1991). This consists of a cylindrical cage of wooden slats held in place
by iron hoops and a ram on a screw thread. The screw thread was turned manually
by means of long bars, forcing the ram onto the pulped fruit. The exuding
liquid was collected in a trough surrounding the cage, similar presses, but
using a perforated cylindrical metal cage are still in use today giving yield
of 55 to 65 percent of the oil present (Sundram, 2003). A recent analysis of
the need for mechanization in the village has concluded that this is still the
most practical implement, because it can be made and maintained locally and is
inexpensive by comparison with other presses (Hornstra et al 1991). The next development in pressing was the introduction
in 1999 of the hand-operated hydraulic press by stock of Amsterdam. This was
capable of processing of 600 to 1,000 pounds of fruit per hour and could
recover 80 percent of the oil present (Kwasi, 2002). The hydraulic mechanism
was later motorized. A different approach to mechanization brought forth the
Colin expeller, which in essence is similar to a domestic mincer. It consists
of a perforated cylindrical cage, fitted with a spiral screw or worm which is
turned manually through a gear. Cooked fruit is fed to the worm through a
hopper and the pressure developed as the worm pushed the fruit forward forcing
oil out through the perforations. Spent fiber and kernels are discharged at the
end of the cage. The machine has a capacity of 100kg cooked fruit per hour or
250kg per hour if motorized (Choo, 1993). The Colin expeller became popular
after 1930, mainly in Cameroon; its limitations were a reduced efficiency with
Dura fruit, which forms the bulk of the wild oil palm crop, rapid wear of the
screw and a relatively high cost (Jason, 2004). The principle of the expeller,
however, has been further developed into the screw press found in all modern
oil mills (Hartley, 1988). The presses described here provided a relatively
efficient process for the step of pressing out the oily liquid during oil
production and led researcher to seek improvements in the other steps. Several
innovations have resulted from a project begun by Nigerian institute for oil
palm research (NIFOR) during the 1950s in cooperation with the food and
agriculture organization of the united nation (FAO) and the United Nations
Development Program (UNDP) (Berger, 1983).
2.2 Methods of Production
Until the early years of the twentieth
century, palm oil was processed only by traditional village methods, by which
loose fruit where collected from the ground or few bunches were cut from the
tree (Jason, 2004). Beginning in the
1920s, however, the united Africa company and British colonial officials in
Nigeria started experimenting with steam cookers and hand presses designed to
make production at the village level more efficient in terms of labour and oil
yield, yet lack of cash prevented most farmer from trying the new machinery,
with the exception of a few lucky recipient of free samples or government
subsidies in 1940s (Pachter, 2007).
A separate process of trial and error
led to the development of the sophisticated factories required to deal with the
volume of fruit produced on modern plantations and to produce oil food
processors. Such factories handle almost all the palm fruit of southeast Asia,
whereas in west Africa and Latin America, processing is carried out by a wide
variety of methods as edible uses in the West. Whatever the scale and
sophistication of the process, it will follow the same procedure which involves
separation of individuals fruit from the bunch, softening of the fruit flesh, pressing
out the oily liquid and purification of the oil (Berger,1983).
The whole ripe fresh fruit bunches are
cut from palm, with young trees this can be done from ground level while in the
older trees in west Africa, harvesting is still often accomplished by a man
climbing the tree secured to it by a loop of rope or other locally available
materials, such as rattan and raffia fiber (Zak,2006). But on plantations, a
curved knife attached to a bamboo is used. After cutting, most of the fruit are
still firmly attached to the bunches, which are divided into a few sections
heaped together, moistened and covered with leaves. Natural fermentation during
two to three days loosens the fruits so that they can be picked off the bunch
sections by hand (Eka and Osagie, 1998).
Oil production is done in two ways,
first, the fruit are separated as soon as the year are loose enough and boiled
with water for 4hours to soften the flesh, which is very fibrous. The cooked
fruit is emptied into a large container, which may be a pit lined with clay, an
iron drum, or a large wooden mortar. This fruit is then reduced to a pulp with
pestles or by treading it under foot. The resulting mash may be diluted with
water, and the oil is skimmed off or squeezed out of the fibrous mash by hand, in
some instances, a sieve made of palm fronds is used to retain the fibers. At
this stage, the liquid product, which contain oil, water, and fruit fibers, is
often boiled up with additional water and skimmed again, although his step is
omitted in some cases, finally, the oil is again heated to boil out the
residual water (Brown, 2005).
Lewkonitsch (2002), reported on the
preparation of small quantities of oil for kitchen use directly from freshly
picked fruit, by boiling the fruit and skimming the oil. Such oil had good
keeping properties and often free fatty acid content below 2 percent but yield
was very low and not available for export. Another method of oil processing is
by allowing the fruit to ferment for 3 or more days longer than in the former
method until the flesh is soft enough. It is then pulped by treading under foot
in an old canoe or pounding in a mortar. Oil is allowed to drain out for up to
3days, then water is added, and the mixture is trodden again, further oil raise
to the surface and is skimmed and finished as in the former methods. (Eka and
Osagie, 1998).
These two processes differ in some
important respects. The prolonged fermentation in the second method of
processing palm oil result in a much greater enzymes breakdown of the neutral fat
and therefore, has a very high free fatty acid content. The yield obtained by
this process is also much lower. However, it has a substantial advantage in
that the labour and fire wood requirements are also much lower. The strong
characteristic flavour developed during both of these processes, as well as the
naturally strong red colour of the oil, are appreciated by local cooks and
visiting gourmets, but they present severe limitations in the export market
(Ayodele, 2010).
The high free fatty acid content and
solid consistency of hard oil (fermented oil) limits its range of uses, making
it well suited to soap boiling but not to food processing. The solid
consistency of hard oil is not due directly to the free fatty acids formed
during the fermentation step but rather to the diglycerides, the other
fragments obtained when one fatty acid is spit from the neutral triglyceride
molecule, (Pachter, 2007).
2.2.1 Steps
Involved In Palm Oil Production (Traditional Method)
1.
Harvesting
2.
Bunch
reception/fermentation
3.
Threshing
(removal of fruit from the bunched)
4.
Sterilization
of bunches (cooking)
5.
Pounding
6.
Pressing
(extraction of the oil)
7.
Heating
8.
Filtering
(purification)
2.3 Physico-Chemical Properties of Palm Oil
Palm oil, like all oils and fats, is
made up mostly of glyceridic materials with some nonglyceridic materials in
small or trace quantities. It is this chemical composition that defines the
chemical and physical characteristics of palm oil, which in turn will determine
the suitability of the oil in various process and application
(Idris, 2006).
Typical
composition of palm oil is presented in table 1. Table 2 presents fatty acid
composition of palm oil. While table 3 shows the glyceride composition of the
oil.
TABLE 1: Constituent of Palm Oil
Constituents Composition
water 0.5%
water 0.5%
Protein
0.0%
Total
carbohydrate 0.4%
Calcium
7mg
Potassium
8mg
Fat
99.1%
Iron 5.5mg
B.
carotene (Equivalent) 27.80Ng
Riboflavin
0.03mg
Source: Hiditch
and William, (1964)
TABLE 2: COMPONENT FATTY ACIDS OF PALM OIL
|
Common Name
|
Systematic
Name
|
Symbol
|
percentage of
total weight palm oil
|
|
Saturated Acid
|
|
|
|
|
Caprylic
|
|
C8.0
|
|
|
Capric
|
|
C10
|
|
|
Lauric
|
n-Dodecanoic
|
|
|
|
Myristic
|
n-Tetradecanoic
|
|
|
|
Palmific
|
n-Hxadecanoic
|
|
|
|
Stearic
|
n-Octadesanoic
|
|
|
|
Arachidi
|
n-Eicosanoic
|
|
|
|
Mono
unsaturated
Palmitoleic
|
n-Hexadec
-9-enoic
|
C16:1
|
<1
|
|
Oleic
|
n-Octadec-9-enoic
|
C18:1
|
40-52
|
|
Gadoleic
|
n-Eicos-9-enoic
|
C20:1
|
<-1
|
|
Poly-
unsaturated
|
|
|
|
|
Acids
|
|
|
|
|
Linoleic
|
n-octadec-9-12
Dienoic C18:2
|
|
5
- 7
|
Sources:
Hilditch and Milliam (1964)
TABLE 3:
Glycerides Components of Palm Oil
Triglyceride Percentage of total triglycerides
Tripalmitrin 3.5
Dipalmitostorin 1.3
Oleo – myristopalmitin 0-5
Oleo – Dipalmitotearin 21 –
43
Palmitode – Olein 10 – 11
Strearode - olein 0 – 6
Linolaodolein 3 – 12
Source:
Hildetch and Williams, 1964
2.3.1 Chemical
Properties of Palm Oil
Triglyceride
form the major component and bulk of the glyceridic material present in palm
oil with small amounts of mono-glycerides and diglycerides, which are artifacts
of the extraction process. The fatty acid chains present in the palm oil
triglycerides could vary in the number of carbons present in the chain and in
structure. It is the variations in the structure and number of carbons in these
fatty acid chains that largely define the chemical and physical properties of
palm oil (Pachter,2007).
The chain length of the fatty acids
present in the triglycerides of palm oil fall within a very narrow range from
12 to 20 carbons(Anwar,1981). Walter (2000) observed that about 50% of the
fatty acids present in palm oil are saturated and about 50% are unsaturated.
This even balance between saturation and
unsaturated. This even balance between saturation and unsaturation determines
the iodine value of the oil (about 53) and confers some stability against
oxidation to the oil as compared to other vegetable oils.
Knowledge
about the detailed structures of the triglycerides present in palm oil is
important because they define some of the physical characteristics of the oil.
(Heber Ashley, 1992). The melting points of triglycerides are dependent on the
structures and position of the component acids present. They also affect the
crystallization behavior of the oil (jason,2004). The semisolid nature of palm
oil at room temperature has been attributed to the presence of the
oleo-disaturated fraction. Partial glycerides are artifacts of the extraction
process, especially the stages prior to sterilization. Oil obtained from
unbrusied sterilized fruit shows trace levels of partial glycerides. Random
analyses of sample of refined palm oil, palm olein, and palm steam have shown
the presence of about 2% of 1,2, diglyderides and about 4% of 1,3-diglycerides
with trace amounts of mono-glycerides. These partial glycerides are important
as they are known to affect the crystallization behavior of the oil (Simeh,
2011).
The carotenoids, tocopheols, sterols,
phosphatides, triterpremic and aliphatic alcohols forms the minor constituents
of palm oil, though present in less than 1% altogether in palm oil,
nevertheless they play a significant role in the stability of oil, in addition
to increasing the nutritive value of the oil (Hartley, 2009).
Crude palm oil contains between 500 and
700ppm of carotenoids mainly in the forms of x –and B carotenes, the precursor
of vitamin A, unless extracted prior to refining, these carotenoids are
thermally destroyed during the deodorization stage in order to produce the
desired color for a refined oil. In crude palm oil, the presence of these
caronoids appears to offer some oxidative protection to the oil through a
mechanism where they are oxidized prior to tocopherols and tocotrienols in the
range of 600-1000ppm. Refined palm oil retains about 80% of these products.
Tocopherols and tocotrienls are antioxidants and provide some natural oxidative
protection to the oil. The combined effects of properties of the carotenoids,
tocopherols, tocotrienols and the 50% instauration of the acids confer on palm
oil a higher oxidative stability when compared to a lot of other vegetable oil.
In term of stenols, palm oil contain far less cholesterol them may other
vegetable oils (Martin, 1988)
2.3.2 Physical
Properties of Palm Oil
The apparent density is an important
parameter from the commercial point of view since it is for volume to weight
conversion; it can also be used as a purity indicator. The solid fat content of
oil is a measure (in percent) of the amount of solid fat present in the oil at
any one temperature. It is measured by means of wide-line nuclear magnetic
resonance spectrometry after a standard tempering procedure for the sample
(Simeh, 2001).
The solid present in the oil at any one
temperature us due to the process of crystallization occurring in the oil as a
consequence of its chemical properties. The different molecular triglyceride
structures with their differing chemical characteristics manifest their
physical states at different temperatures, thus imparting certain
crystallization and melting behaviour to the oil (Bonnie, 2000). Hilditch and
Williams (1964) reported typical physical properties of palm oil as shown in
table 4
TABLE 4:
Physical Properties of Palm Oil
PROPERTY VALUE
Density
(kg/m3)
Specific
gravity 0.921-0.9240
Viscosity
(g) 0g
Melting
point (0c) 27-500c
Boiling
point (0c) 00c
Flash
point (0c) 290-320oc
Smoke
point 215-330oc
Colour
26-28
yellow
Source:
Hilditch and Willaims (1964)
2.3.3 Characterization
of Palm Oil
Palm
oil can be characterized by the free fatty acid/acid value, peroxide value,
saponication value, iodine value and melting point.
Free Fatty Acid/Acid Value
This
is a measure of the amount of free fatty acid present in fat/oils. Some of the
deterioration that take place during storage of either the raw materials from
which the fat is obtained, or in the oil/fat itself after isolation, results in
hydrolysis of triglycerides to yield free fatty acids (Ihekoronye and Ngoddy,
1985).
Peroxide Value
This is usually used as an indicator of
determination of oil/fats. As oxidation takes place, the double bonds in the
unsaturated fatty acids are attacked, forming peroxides. This breakdown to
produce secondary oxidation, product which indicates rancidity. The peroxide
value can therefore be used to estimate oxidation, but as the compound formed
is unstable and oxidation proceeds further. It is not a complete measure of
oxidation (Ihekoronye and Ngoddy, 1985).
The
peroxide value is usually less than 10 gramme of a fat sample when the sample
is fresh. During storage of most fats, the peroxide value shows little increase
in the early stages, known as induction period, after which there is a marked
increase. Peroxides value (PV) of oil is a measure of its content of oxygen
(Onwuka, 2005,) fresh oils usually have peroxide value below 10meq/kg. A rancid
taste begins to show up when the peroxide value is between 20 to 40meq/kg.
Saponification value:
Saponification value of fat or oil can
be defined as the number of milligrammes of potassium hydroxide required to
neutralize the fatty acids resulting from the complete hydrolysis of 1g of the
sample. Saponifacation values are usually large when compared with the acid
value of most edible oils.
The
saponification value is inversely proportional to the mean mol. wt of the fatty
acids in the glycerides present (Onuuka, 2005).
Iodine Value
Iodine value measures the degree of
unsaturation in vegetable oils. This value for oil or fat is defined as the
weight of iodine absorbed by 100 parts
by weight of the sample. The glycerides of the unsaturated fatty acids present
with a definite amount of halogen and the iodine value is therefore a measure
of the extent of unsaturation. Iodine value is constant for a particular oil or
fat, but the exact figure obtained depends on the particular techniques
employed.
Melting Point:
This is the temperature at which the oil
in its solid state changes to liquid. SON (2002). States that palm oil should
have melting point of 27-500C. the melting point is due to low
molecular weight of its glycerides.
2.4 Uses of Palm Oil:
Palm oil is extracted from the mesocarp
of ripe fruit. In a milling process a semi-continuous process involving
sterilization, bunch stippling oil extraction oil clarification and
purification. Palm oil so obtained is about the most suitable fatty materials
for the many used of vegetable oils and fats.
2.4.1 Edible
Uses of Palm Oil
As a food commodity palm oil is the main
cooking oil in most part of Nigeria. It greatly contributes to a balanced diet
because of its high content of vitamin A (carotene) which imparts the rich red
colour to the oil.
Palm
oil is used in the manufacture of cooking/frying oil, margarine, shortenings
which are used in making bread, cakes, cream and sweet. It is also used as an
additive in the manufacture of livestock feeds.
Use in
margarine, confectionary, ice cream, filled milk and as cocoa butter
substitute.
Bleached and refined palm oil is used in
the manufacture of margarine (through a hydrogenation process) and of confectionary,
Ice-creams, filled milk or cocoa butter substitutes because Lauric acid (kernel
oil) is less prone to Oxidation, the dried coffee whitener made from lauric
oils has a longer shelf life than the corresponding product made from natural
milk.
Sources of
Vitamin A and E
Palm
oil content Carotene and tocopherol which are sources of vitamin A and E
respectively.
2.4.2 Non-Edible Uses of Palm Oil
Palm oil is used in the manufacture of
soap, indeed, the soap industry is the largest non-edible user of palm oil and
is used to the practical exclusion of other oils in the tine plate industry
(metallurgy) because it is relatively cheep and has a fairly good composition
for the purpose. During the tinning process palm oil produces fatty acid and
other compounds which assist in dissolving metallic oxide to promote uniform
coating of metal by the oil. Palm oil may be used in the treatment type of
cream ointments and lotions since it is more readily absorbed by the skin than
mineral oil. Palm oil is also used for non drying products like in bleaching
oils for illumination and to a limited extent may be used as diesel engine
fuel. Palm oil may also be used as one of the components in making lubricants.
It can also be used in the manufacture of candles and polish.
Soap
manufacture:
Saponification of palm oil with caustic soda
produces soap (as well as glycerin).
Production of
Useful Olechemical
Hydrolysis
of fats produces fatty acid and glycerol. Glycerin is used among other uses as:
Emulsifiers
in the food processing and pharmaceutical industry.
Some
other useful application of glycerin include the production of toiletries,
tobacco, alkyd resins, paints and varnishes, cellophane, explosives
polyuretheane and many other uses/application.
As Source of
Energy
Oil palm
products are useful as a source of energy in firing boilers (empty fruit
bunches, kernel shell and fibre) and as biodiesel (crude palm oils and
fractions) for power generation and recently as fuel for cars.
2.5 Standard
Specifications
The
standard specification of palm oil is presented in the Table 5 below.
Table 5: Quality
standard of palm oil
Parameter value
Unsaponifiable
matter (g/kg) 10
Peroxide
value (meg/kg) 10
Free
fatty acid (%) 3.5
Saponification
value (mgkoH/gl) 195
– 205
Iodine
value (wijis) 45
– 55
Relative
density (400C/H20 at 200C) 0.898-0.907
Refractive
index (nD 400C) 1.453-1.459
Total
carotenoids (mg/kg) 5000-2000
Anisidine
value (meg/kg) 5.0
Moisture
% 0.2
Colour
25-30 red/26-28
yellow
Total
gylceride (%) 98.5-99.5
Melting
point rang (0C) 27-50
Sourse:
Son,2000