PALM OIL | TRADITIONAL AND MECHANIZED METHODS OF PRODUCTION | THE HISTROY, PROPERTIES AND CHARACTERISTICS



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%
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
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