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Palm Oil - Composition and Properties

1. Composition of Palm Oil

Palm oil is extracted from the mesocarp of the fruit of the palm Elaeis guineensis. The mesocarp comprises about 70 – 80% by weight of the fruit and about 45 -50% of this mesocarp is oil. The rest of the fruit comprises the shell, kernel, moisture and other non-fatty fibres. The extracted oil is known as crude palm oil (CPO). Palm oil like all natural fats and oils comprises mainly triacylglycerols, mono and diacylglycerols. Other components are free fatty acids (FFA), moisture, dirt and minor components of non-oil fatty matter referred to collectively as unsaponifiable matter. CPO produced in Malaysia in the average will contain about 3.5% FFA, 4.7% diacylglycerols, 0.2% monoacylglycerols, 0.25% moisture and impurities, 1% minor components and balance 90.35% of triacylglycerols.

Triacylglycerols (Triglycerides)
Triacylglycerol is the basic unit of oils and fats that determines their characteristics. The type of fatty acid, as well as the distribution across these positions, determines the characteristics of the oils/fats.

Triacylglycerol is a chemical compound consisting of three elements; carbon, hydrogen and oxygen. These elements make up molecules of fatty acids and glycerol, which combine to form fat molecules known as triacylglycerols. Triacylglycerol means there are three (tri) molecules from the acyl group (carboxylic acids) attached to a glycerol molecule. In the case of oils & fats, the carboxylic acids consist of fatty.

hydrolisis of triglyceride

Where Ra, Rb, Rc represents the hydrocarbon chain in a fatty acid molecule.        

Fatty acids are defined as compounds that are composed of long chains of carbon and hydrogen atoms (referred to as hydrocarbon molecules) containing a carboxylic acid moiety at one end (a carboxylic acid is written –COOH). The numbering of carbons in fatty acids begins with the carbon of the carboxylic acid group. Fatty acids hydrocarbon chain consist mainly of even number of carbons (from 4 to 28)

Fatty acids differ from one another in:

(1) Length of the hydrocarbon tails

(2) Degree of unsaturation (double bond)

One of the main parameters influencing the characteristics of fats and oils is the degree of unsaturation of their fatty acids.

Fatty acids may be saturated, monounsaturated or polyunsaturated. If every carbon atom has its full quota of hydrogen atoms, the fatty acid is saturated.

Table of Saturated Fatty Acids

Examples of saturated fatty acids.

The fatty acids are labelled according to the number of carbon in the molecule as indicated in the column ‘chain’. Note that as the number of carbon increases, the melting point also increases.

If there is a double bond in between the carbon atoms of a fatty acid, it is known as monounsaturated. If there is more than one double bond in a fatty acid, then it is known as polyunsaturated.

Fatty Acids - 2

Most of the saturated fatty acids occurring in nature have unbranched structures with an even number of carbon atoms. An unsaturated fatty acid with a double bond can have two possible configurations, either cis or trans, depending on the
relative positions of the alkyl groups. Alkyl group refers to the carbon-hydrogen chain of the fatty acids.

Fatty Acid Isomerism - 2

cis-trans isomerism modelIsomers are defined as compounds with the same molecular formula but different molecular structure. The picture above shows cis-trans isomerism where the molecule has two possible orientations.  The terms cis and trans are from Latin, in which cis means “on the same side” and trans means “on the other side”

Most naturally occurring unsaturated fatty acids exist in the cis configuration. Most fatty acids in the trans configuration (trans fats) are not found in nature and are the result of human processing.

Table of Saturated and Unsaturated Fatty AcidsEffect of carbon chain length and unsaturation on melting points of fatty acids

 

NOTE – Fatty Acid Nomenclature
18:2 9c 12c
18        – indicates the number of carbon in the molecule,
2          – indicates the number of double bonds,
9c        – indicates the location of double bond from the carboxyl end and c indicates
cis configuration.
12c      – Since this fatty acids has 2 double bond, the 2nd double bond is indicated on
the 12th carbon with a cis configuration.

Note that from the table above, the longer the carbon chain (i.e C16 and C17) , the higher the melting point. But once there is a double bond (i.e C18 and C18:1), the melting point drops significantly. If more than one double bond exists, the melting point drops further (C18:1 and C18:2).

Table of Fatty Acids Melting Points

Cis isomers will also have a lower melting point compared with its equivalent trans isomer. An example is C18:3 cis configuration has a much lower melting point than C18:3 trans configuration.

(3) Position of the double bonds in the chain

Table of Common Fatty AcidsFrom the table above, with reference to C18:3 linolenic fatty acids, the different locations of the double bonds define the type of fatty acid and its functionality. The omega-3 linolenic acid is called alpha-linolenic acid which has three double bonds at 9,12,15 positions, whereas gamma-linolenic acid, omega-6 linolenic acid, 6,9,12 positions.

Linolenic Acid Structure

The  distribution of the 10-12 main fatty acids over the three different positions of the glycerol molecule determines the properties of the oils/fats. Therefore, great efforts are undertaken to separate certain triacylglycerols or to change their distribution in the glycerol molecule.

Since there are a number of different fatty acids that occur in natural fats, a great many different triglycerides are encountered in nature. These are named according to the fatty acid or acids they contain. Thus triolein is the triglyceride of oleic acid, tripalmitin that of palmitic acid, tristearin that of stearic acid, while monopalmitin-distearin contains, as the name indicates, one molecule of palmitic and two of stearic acid. While a large variety of fatty acids is found in natural fats and oils, only a few of them are of outstanding commercial importance. These are myristic acid, lauric acid, palmitic acid, stearic acid, oleic acid, linolic acid, and linolenic acid. Though the number of triglycerides encountered in nature is great, the triglycerides of these seven acids (see table of formulas below) make up the great bulk of the natural fats and oils.

lauric (12:0, 4%),
myristic (14:0, 2%),
palmitic (16:0, 11%),
stearic (18:0, 4%),
oleic (18:1, 34%),
linoleic (18:2, 34%),
α-linolenic (18:3, 5%)
erucic (22:1, 3%).

Fats and oils are practically always mixtures of triglycerides in varying proportions.

Fatty Acid Composition of Common Edible Oils and Fats

Palm oil is distinguished from other oil by its high level of palmitic acid (C16:0). Unlike other vegetable oil, palm oil also contains almost equal quantities of saturated (palmitic 45% and stearic acid 4%) and unsaturated acids (oleic 40% and linoleic acid 10%).

Mono, Diacylglycerols and Free Fatty Acids (FFA)

In the presence of heat and water the triacylglycerols break up by a process known as hydrolysis to form free fatty acids thus yielding mono and diacylglycerols and FFA Mono- and diacylglycerols are not significant components of good quality oils, but elevated levels may be found in badly stored fruits due to hydrolysis. The reaction can be autocatalytic, or catalysed by some metals or by the enzyme lipase, which is widely found in living organisms and is also present in oil palm mesocarp. The first stage is a partial hydrolysis, the products being FFA and diglycerides (glycerol with two fatty acids attached).

Graphical Representation of Triglycerides

Hydrolysis can take place in the pre-harvest and post-harvest handling and storage, during oil extraction, crude oil storage, and shipping. This is undesirable as the result is an elevation of the concentration of FFA in the crude oil. Great attention should be given during the various steps of the process to minimize the amount of FFA in the starting or finished oil products. High FFA in crude oil will cause greater refining loss.

During harvesting, hydrolysis of triglycerides does not occur in undamaged fruit, presumably because the lipase is compartmentalised within the cell and only comes into contact with the oil if cell membranes are damaged. It is therefore essential to minimise bruising or damaging of the fresh fruit before it reaches the mill, where the enzyme, together with any microbial lipases, is inactivated by sterilisation. During storage and transportation, care should be taken to prevent the oil from being contaminated by moisture or metal (especially copper or bronze), all which promote hydrolysis.

Good oils having lower amount of mono and diglycerides is said to be of great importance in the fractionation process because they act as emulsifying agents inhibiting crystal formation and making filtration difficult. Industrially, mono and diacylglycerols are produced by partial hydrolysis or glycerolysis of triacylglycerols for use as food grade emulsifiers.

Fatty acids can used as animal feed or sold to oleochemical producers for production of soaps and other specialised chemicals.

Moisture and Impurities

This is a result of mainly milling practice. Iron impurities are derived from the wear and tear of oil mill machinery and can be minimised by using stainless steel at strategic points in the milling process. Good milling will reduce moisture, dirt as well as metal contamination in palm oil.

Trace quantities of copper, iron, manganese, and nickel substantially reduce the oxidative stability of fats and oils, whereas calcium, sodium, and magnesium reduce the efficiency of the refining, degumming, bleaching, and hydrogenation systems. The metals effects can be diminished by the use of chelating agents at various processing points to sequester the trace metals. The most widely used chelating agents are citric and phosphoric acids.

Pesticides are used to increase agriculture production throughout the world. Studies have shown that a majority of the pesticides applied eventually reach the soil surface, where they gradually spread, translocate to other environments, or eventually degrade. Translocation to oil-bearing plant seeds has also been demonstrated. Processing studies have shown that neither solvent extraction nor bleaching affects the pesticide levels in oils; however, it was found that pesticides are removed by volatilization during deodorization.

Minor Constituents

Crude palm oil contains approximately 1% of minor constituents including carotenoids, tocopherols, tocotrienols, sterols, phospholipids, triterpene alcohols, squalene, aliphatic alcohols and aliphatic hydrocarbons. The major components of interest are the carotenes, tocopherols, tocotrienols, sterols and squalene. Carotenes and tocopherols are antioxidants and stabilise the oil against oxidation. During refining, the bleaching and steam deodorisation processes partially remove some of these valuable components. The amounts retained in the refined oils depend on the conditions of refining.

Minor Components of CPO

Carotenoids

Carotenoids are a family of compounds of more than 600 fat-soluble plant pigments that provide much of the colour we see in nature. They produce the beautiful colours of many birds, insects, and marine animals as well as the colours of many flowers and fruits.

The dark red-orange colour of oil palm fruit is due to the high concentration of carotenoids and anthocynanins. Crude palm oil, extracted commercially by sterilisation and press, contains 500–700 ppm of carotenoids, the variation being due to process conditions, species of oil palm and level of oxidation. The major components are α-carotene and β-carotene.

Composition of Carotenoids in POCarotene Contents in Palm Fractions

α-Carotene and β-carotene are also demonstrated for their provitamin A activity, with β-carotene being the most potential provitamin carotenoids. Carotenoids have long been known for their pro-vitamin A activity, as they can be transformed into vitamin A in vivo. Vitamin A is necessary for vision, growth, cellular differentiation, morphogenesis, and several other cellular and physiologic functions. Besides the role of providing a source of vitamin, carotenoids are considered to have anti-carcinogenic properties

Crude palm oil contains the highest concentration of natural carotenoids, which proves it to be the most promising plants for carotenes sources in nature.

Physically refined oils show no trace of the carotenoids. These are either absorbed onto the bleaching earths or destroyed during thermal treatment. Carotenes preferentially segregate into the more unsaturated olein fraction, leaving little in the stearin fraction. This has important consequences for the oxidative stability of these two fractions

Tocopherols and tocotrienols

Tocols, natural antioxidants found in plant-based oils, include four tocopherol and four tocotrienol isomers, each designated as alpha (α), beta (β), gamma (γ), and delta (δ) depending on the number and position of methyl groups on a chromane ring; they also possess vitamin E activity. Tocotrienols have become a focus of research in recent years because of findings showing high efficacy in protecting against heart related diseases and certain cancers. In addition to anticancer effects, tocotrienol-rich fractions of palm oil have hypocholesterolaemic effects in humans and offer protection against heart diseases.

Content of Tocopherols and Tocotrienols in Oilstoc –tocopherols
T3 – tocotrienols

Tocotrienols are extracted commercially from palm oil and rice bran oil. The common commercial source of natural vitamin E (soy, corn, cottonseed, sunflower, and canola oil) contained little or no tocotrienols. Crude palm oil, besides being rich in vitamin A, also has a high content of vitamin E, present as tocopherols and tocotrienols of which 70% are tocotrienols.

Physical refining invariably causes some loss (15-57%) of the tocopherols; therefore, over vigorous conditions need to be avoided.  The practical method to extract vitamin E is from palm fatty acid distillate (PFAD), in which the total tocopherols and tocotrienols are concentrated to 0.4–0.5% (w/w).

Composition of PFADCrude palm olein has a higher content of tocopherols and tocotrienols. Refined oils retain about 70% of the tocols, the amount varying depending on conditions of refining. Most of the loss occurs at deodorisation, and consequently palm fatty acid distillate (PFAD) has up to five to ten times the level in crude oil.

Vitamin E Content in Palm Oil

Sterols

Sterols are high-melting polycyclic alcohols of the general structure:

General Structure of Sterol

Phytosterols or plant sterols form a major part of the unsaponifiable fraction of palm oil. They may occur in the free form, or the hydroxyl group may be esterified by a fatty acid such as linoleic acid, yielding a wax-like arrangement. They may also be present as glucosides.

Phytosterols are important structural components of plant membranes. In palm oil sterols, sitosterol (60%), campesterol (13%) and stigmasterol (24%) are the major constituents while a minor amount of cholesterol (3%) is present.

Sterol Composition of Palm Oil

Phytosterols have been the subject of many nutritionists because of their bioactivities such as cholesterol-lowering actions and anti-cancer effects. There is growing interest in developing functional foods, including vegetable oils, spreadable fats, butter, yogurt, bakery products, juice, and milk, in which different types of phytosterols are intrinsic or just added as novel food ingredients to fortify the health-promoting effect of those products. At present, some products containing phytosterols are available in the market, especially in several European countries.

Unlike tocotrienols and carotenes, the content of phytosterols in palm oil is relatively lower than that in other oils. The main source of phytosterols in large scale production is the by-products from the process of refining oils. Those by-products are known as fatty acid distillate (FAD). The deodorization step of refining process not only strip FFA and volatile odiferous components, but also remove minor components such as tocopherols, tocotrienols, and phytosterols into the distillate. Therefore, phytosterols are concentrated in the FAD, and this is the common industrial method to obtain phytosterols from vegetable oils since the concentration of phytosterols intrinsic in vegetable oils is low.

Minor Components of CPO - 2

Phospholipids (Gums)

Complex esters which contain phosphorus, nitrogen bases, sugars, and long-chain fatty acids are classed as phospholipids. They are similar to oil molecules (Triglycerides) except that they are phospholipids products where one of the three fatty acid chains is substituted by a phosphatide.

Crude palm oil contains polar lipids such as phospholipids and glycolipids with the former receiving considerable attention because of the suspected deleterious effect of phosphorus on oil quality. Inorganic phosphorus and phospholipids are two forms of phosphorus compounds in CPO, with inorganic phosphorus being the most predominant. Phospholipids in palm oil are relatively low (5–130 ppm or 0.2–5 ppm as P) since only 4% of the phospholipids of the palm fruit remains in the CPO during the wet milling process.

Phosphatides, as the principal constituent of gums in the crude oil, severely interfere with the efficiency of subsequent process steps if allowed to remain. Phosphatides darkens the colour of an oil if they become broken down by heat; and can lead to impaired flavour stability. The main responsibility for this last ill-effect, however, is linked with traces of pro-oxidant iron liable to persist in refined oil along with the gummy material rather than phosphatides themselves. Inorganic phosphate is observed to increase with the content of free fatty acid and pro-oxidant metals, especially in poor quality oils. Residual phosphorus in bleached and deodorized oil caused by poor processing or treatment also is known to correlate well with the free fatty acid escalation during transport. Glycolipids, although present in larger amounts than phospholipids, do not appear to contribute much to the quality of crude palm oil.

Both glycolipids and phospholipids are almost completely removed in refining processes; therefore, their content in commercial palm oil is very low.

Phosphatides can be either soluble or weakly soluble in water and thus giving rise to two types of gums:

• Non-hydratable gums       – Can be removed by acid treatment
• Hydratable gums               – Can be removed by water washing.

Ubiquinone

Ubiquinone is another interesting and valuable minor component present in palm oil. The oil-soluble, vitamin-like substance structurally resembles with vitamin K, which includes a 1,4-benzoquinone head and a side chain consisted of 6–10 isoprenyl subunits. Coenzyme Q10 (CoQ10) is the most common ubiquinone in palm oil. The CoQ10 were report to be about 10–80 ppm in CPO.

Squalene

Squalene is a triterpene with 30 carbon atoms, containing six isoprene units, and it is known as an intermediate in the biosynthesis of sterols. Squalene is reported to have anti-carcinogenic activity against skin, colon, and lung cancer. In addition, squalene is a powerful antioxidant which can scavenge free radicals from the body and thus reduce free radical oxidative damage to the skin. Squalene in CPO, refined oil, pressed fiber oil, and PFAD are reported to be 200–600 ppm, 415 ppm, 1000–1800 ppm, and 12,000–18,000 ppm, respectively.

Reference:
1. Palm Oil Quality Standards for Trading, MPOB, 2013
2. World Conference: Processing of Palm, Palm Kernel and Coconut Oil Proceedings,  AOCS, 1985
3. Refinery of Palm Oil, Lim Jit Kang, USM
4. IUPAC Compendium of Chemical Terminology (2nd ed.). International Union of Pure and Applied Chemistry. 1997
5. Introduction to Oils & Fats Technology, AOCS Press, 2000
6. Bailey’s Industrial Oil and Fat Products, Wiley, 2005
7. Vegetable Oil in Food Technology, Blackwell Publishing, 2002
8. Palm Oil: Production, Processing, Characterization and Uses, AOCS Press, 2012
9. Fats and Oils: Formulating and Processing for Applications, CRC Press, 2009

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6 thoughts on “1. Composition of Palm Oil

  1. okay

    Posted by bob | February 28, 2017, 2:42 am
  2. I really appreciate this, helpful though. Good job

    Posted by EBENEZER | August 30, 2017, 6:02 pm
  3. I really appreciate this, helpful though.

    Posted by EBENEZER | August 30, 2017, 6:02 pm
  4. Very educative and full of details.

    Posted by Anyadioha Kenneth | June 4, 2021, 11:02 pm

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