Malaysian Journal of Analytical Sciences, Vol. 7, No. 1 (2001) 93-96
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Effects of Monoglycerol Stearate and Free Fatty Acids on the Melting Point
of Palm Olein
Dzulkefly K1, Wan Rusmawati W M3, Wen-Huei Lim2, Anuar K1, and Hamdan S4
Department of Chemistry, Universiti Putra Malaysia (UPM)
Advanced Oleochemical Technology Centre (AOTC), Malaysia Palm Oil Board (MPOB)
3
Department of Chemistry, Universiti Pendidikan Sultan Idris (UPSI)
4
Faculty of Science and Technology, University College Terengganu
1
2
(Received 6 September 2000)
Abstract. RBD palm oil was fractionated by using various solvents to obtain olein and stearin fractions. The triglyceride
(TG) content of palm olein was then determined to find the best solvent for the fractionation process. The effects of
monoglyceride (MG) and free fatty acid on the melting point of the fractionated palm olein were also studied. The result
showed that acetone was probably the best solvent for fractionation of palm oil in respect to olein yield and triglyceride
content. On the other hand, the presence of MS (monoglycerol stearate) increased the melting point of palm olein, whereas the
free fatty acid reduced it.
Abstrak. Pemeringkatan minyak sawit RBD untuk mendapatkan pecahan olein dan stearin telah dilakukan dalam berbagai
pelarut. Kandungan trigliserida (TG) dalam pecahan olein kemudian ditentukan untuk mendapatkan pelarut terbaik bagi
proses pemeringkatan tersebut. Kesan kehadiran monogliserida (MG) dan asid lemak bebas ke atas suhu lebur pecahan olein
juga dikaji. Keputusan menunjukan bahawa pelarut asiton mungkin yang terbaik bagi pemeringkatan minyak sawit tersebut
jika dilihat dari peratus olein dan kandungan TG. Kehadiran MS (monoglisirol stearat) telah didapati menaikan suhu lebur
olein sawit tersebut, tetapi sebaliknya, asid lemak bebas didapati menurunkan suhu lebur.
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Key words: palm oil, palm olein, melting point, free fatty acid, fractionation
Introduction
Palm oil is a complex mixture of glycerides but can
be fractionated into liquid olein and solid stearin
fractions [1]. Olein fraction is used for frying
purposes (both in the industry and at home) mainly in
tropical climates [2]. However, high-quality cooking
oil is expected to remain liquid during storage.
Malaysian palm olein has relatively higher melting
point of 22-24oC [3], thus its tends to crystallize
during storage at temperature below 20oC. The
crystallization of palm olein is caused by the presence
of high-melting triglycerides and non-oil components,
namely monoglyceride (MG), diglyceride (DG) and
free fatty acids. These components have significant
effect on the melting point of palm olein and their
existence in palm olein depend greatly on the
efficiently of the fractionation process. In a solventfractionation process, the polarity of solvent used will
determine the amount of MG and DG retained in the
fractionated palm olein, thus its melting point. The
DG contents of palm olein were found between 4-6 %
and 5.1-5.8 % when fractionated using acetone and
hexane solvents respectively at temperatures between
19-20oC [4]. It was also reported that during
fractionation, diglycerides inhibited crystallization
that led to loss of olein (low yield of olein). On the
other hand, saturated MG increases the melting point
of vegetable oil, whereas with unsaturated MG, the
melting point decreases. Recently, monounsaturated
triglycerides (POP, POS) are known causing early
crystallization of palm olein during storage at
temperature below 25oC [5].
There is limited report on the effect of
various solvents on the properties of fractionated palm
olein. In this paper, we report the effects of solvent
on the yield and triglyceride content of fractionated
palm olein. The effects of adding monoglyceride and
free fatty acids on the melting point of fractionated
palm olein were also studied.
Materials and Method
Materials
Malaysian RBD palm oil and palm olein were
obtained from a local oleochemical company.
Standard triolein was purchased from Sigma
Chemical Co. and monoglycerol stearate was obtained
from Palm Oleo, Rawang. The organic solvents used
were: diethyl ether, ethylacetate, n-pentene, petroleum
ether, n-hexane, acetone, cyclohexane, toluene,
isooctane and propanol. All solvents were of high
purity and used as received.
DZULKEFLY K et al.: EFFECTS OF MONOGLYCEROL STEARATE AND FREE FATTY ACIDS
Methods
Effect Of Monoglycerol Stearate And Free Fatty
Acids On The Melting Point Of Palm Olein.
Fractionation of RBD palm oil into palm olein and
palm stearin
RBD palm oil was heated at 70oC until it melt
completely before used. Samples of heated palm oil
(about 10 g) were then dissolved in various organic
solvents, at ratio of palm oil to solvent of 1:10 (v/v)
and held at the fractionation temperature (4oC) for 24
hours to allow complete crystallization.
The liquid fraction (palm olein) was then
separated from the solid stearin by vacuum filtration.
The solid stearin was washed with 3x20ml cold
solvent to remove traces of olein. Palm olein,
obtained after removal of solvent by rotary
evaporation, and the solid stearin were then dried
under vacuum to remove traces of solvent and
weighted.
The triglyceride content of the fractionated
palm olein was determined by using HPLC (JASCO
UV-970) equipped with a normal phase silica column
(ECONOSIL SI10U, 250 mm length and 4.6mm i.d).
A mixture of isooctane:propanol (94:6, v/v)
was used as mobile phase with a flow rate of 1ml/min.
The triglyceride was detected using UV detector set at
213 nm. The external standard method was used to
determine the concentration of triglyceride in olein
fraction and a calibration curve was prepared using
pure triolein.
RBD palm olein sample (about 5.0 g) was mixed with
various percentage of monoglycerol stearate (MS)
before being melted at 70oC to homogenize. The
mixture was then freezed at 0oC for 24 hours before
subjected to differential scanning calorimetry (DSC)
analysis. The weight percents of monoglycerol
stearate used were: 0%, 2%, 4%, 6% and 8%. The
melting point of the mixtures was determined from
the DSC curve. The same procedure was repeated
using lauric and oleic acids. The weight percents of
acid added to palm olein were: 0%, 2%, 4%, 6% and
8%.
Results and Discussion
Palm oil consists of mainly triglycerides of different
polarity. It can be fractionated into liquid fraction
(olein) and solid fraction (stearin) using organic
solvent. The polarity of solvent used is greatly
influenced the yield of olein and stearin fractions.
Table 1 shows the yield of olein and stearin fractions
after fractionated using various organic solvents.
Hexane gave the highest percentage of olein (88.4%),
followed by cyclohexane (86.7%), petroleum ether
(85.3%) and others. It was also observed that
sedimentation occurred in the olein fractions obtained
by using diethyl ether, toluene and cyclohexane after
a few days storage at room temperature. The
sediment was probably due to incomplete
crystallization.
Table 1: Effect of solvent on the yield of palm olein and palm stearin fractions and the triglyceride (TG) content of
palm olein
Solvent
Acetone
Cyclohexane
n-Hexane
Petroleum ether
n-pentane
Ethyl acetate
Diethly ether
Toluene
Yield of Olein
(%)
73.6
86.7
88.4
85.3
80.0
79.3
77.0
83.8
A good palm olein quality should contained
high TG content, and low non-oil components.
Results from this study showed that fractionation
using acetone gave the highest TG content (84.1%) in
olein fraction, whereas toluene gave the lowest
(64.8%). Other solvents - cyclohexane (81.4%) and
diethyl ether (82.9%) obtained more than 80% TG.
94
Yield of Stearin
(%)
26.4
13.3
11.6
14.7
20.0
20.7
23.0
16.2
TG Content of
Olein Fraction (%)
84.1
81.4
78.1
65.5
65.5
62.9
82.9
64.8
Based on the high yield of olein (86.7%) and TG
content (81.4%), cyclohexane should be the best
solvent for fractionation of palm oil. However,
cyclohexane was not able to remove completely from
the product, therefore, acetone is more suitable
solvent for fractionation of palm oil.
DZULKEFLY K et al.: EFFECTS OF MONOGLYCEROL STEARATE AND FREE FATTY ACIDS
A
B
C
D
A: palm olein + 0% MS
B: palm olein + 2% MS
C: palm olein + 4% MS
D: palm olein + 6% MS
Figure 1: DSC thermograms of fractionated palm olein with adding monoglycerol
stearate (MS).
Effect Of Monoglycerol Stearate And Free Fatty Acid
On The Melting Point Of Palm Olein
MS. Figure 2 shows a linear correlation between the
melting point of palm olein and the percentage of MS.
The effect of monoglycerol stearate (saturated MG) in
fractinated palm olein was study by differential
scanning calorimetry (DSC). The melting point of
fractionated palm olein obtained in this study was
very low, about 5.7oC, as compared to that of normal
palm olein, which is about 22-24oC obtained from
fractionation at 22oC. Figure 1 shows a typical DSC
thermogram of fractionated palm olein in the presence
of monoglycerol stearate (MS). It was observed that
the melting curve of palm olein was shifted to the
high temperature region with increasing amount of
In contrary, the melting point of palm olein
decreases with free fatty acid. Figure 3 depicts a
significant reduction of melting point with increasing
the percentage of lauric (C12:0) and oleic (C18:1)
acids respectively.
Lauric acid caused greater
reduction in melting point as compared to oleic acid.
The main reason was probably due to the shorter fatty
chain of C12 as compared to C18:1. Therefore, the
observed melting point of palm olein is actually a
result of a combination of these two effects, i.e.
partial glycerides and free fatty acid contents.
8
6.5
6
Temperature, oC
o
Temperature, C
7
6
5.5
4
2
5
0
4.5
0
2
4
6
8
10
% MS
Figure 2 : Effect of monoglycerol stearate (MS) on the
melting point of palm olein
0
2
4
6
% of lauric and oleic acids
8
10
Figure 3: Effect of lauric (♦) and oleic (•) acids on the
melting point of palm olein.
95
DZULKEFLY K et al.: EFFECTS OF MONOGLYCEROL STEARATE AND FREE FATTY ACIDS
Conclusion
Acetone is the best solvent for fractionation of palm
oil because it gives the highest triglyceride (TG)
content in olein fraction. The presence of unsaturated
monoglyceride in palm olein resulted an increase of
melting point, whereas free fatty acids reduced the
melting point.
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