International Journal of Chemical, Environmental & Biological Sciences (IJCEBS) Volume 2, Issue 1 (2014) ISSN 2320–4087 (Online)
Flow Behavior of Olive Oil Grown in West of
Libya
Esam A. Elhefian

II. MATERIALS AND METHODS
Abstract—This work is focused on studying the influence of
A. Materials
The virgin olive oil utilized in this work was obtained from
a mill located in Sabratah city, west of Libya. All samples
were kept at room temperature in a dark place until analysis.
Every value taken is an average of three measurements. Data
points in the figures are mean  standard deviation (SD).
temperature and storage time on the rheological properties of some
samples of virgin olive oil as a function of time. Results showed that
Newtonian behavior was pronounced at temperatures from 10°C to
50°C for all types of olive oil used. Studying the effects of shearing
and storage times on the apparent viscosity of all samples did not
show any significant differences at all shearing times applied in this
study. In addition, it was found that all types of olive oil obeyed the
Arrhenius equation.
B. Rheological measurements
Rheological measurements were performed on a Brookfield
digital viscometer, model DV-II + Pro, with an attached UL
adapter. The viscosity was determined in 20 mL of the sample
in each analysis and the shearing time was 15 second. For the
storage time measurements, solutions were kept at room
temperature in glass bottles in a dark place until analysis.
Temperature was controlled using a water bath with precision
of ±1oC. Analysis was done in a temperature range of 10–
50oC and measurements were done in different shear rates.
Each measurement was recorded as an average value of five
readings when a constant shear rate was applied.
Keywords—Apparent viscosity, olive oil, rheology, shear
stress
I. INTRODUCTION
O
LIVE oil is a complex mixture of a number of
compounds such as fatty acids, vitamins and phenolic
compounds. This mixture of chemical compounds is
believed to be able to provide good health benefits to the users
(1). For this reason, the olive has been a significant product
for people of the Mediterranean countries for a long period of
time. Many studies were carried out to find how best the oil
could be stored without loss of its quality. Special care should
be taken into account when storing olive oil. Several methods
have been suggested in order to solve the problem of storage
(2-5). Among the factors that can affect the olive‘s shelf life
are light and temperature. Heating or keeping the oil at high
temperature will surely age it. This will make the oil rancid.
On the other hand, storing olive oil at low temperature
however, will greatly extend its shelf life (6). Thus it is
recommended to store olive oil in a dark cool place in tightly
closed dark glass bottles.
Rheology has been applied to study the behavior of
solutions, mixtures and suspensions [7]. Among important
parameters in food industry, viscosity plays an important role.
It is an important factor to determine the quality and stability
of a food system and to characterize the fluid texture [8,9]. As
with pure olive oil, it has been observed that there is a
decrease in its viscosity, hence quality after certain time of its
pressing, which makes it necessary to be consumed within this
certain time.
The objective of this work is to study the effects of
temperature and storage time on the apparent viscosity and
shear stress of olive oil.
III. RESULTS AND DISCUSSION
In this study, the shear rate-dependent viscosity of some
samples (fresh, 1 year and 2 years) of olive oil as a function of
shear rate at a temperature range of 10oC to 50oC is presented
in figure 1. Similar to that of many fluids, the behavior of the
viscosity–temperature interrelationship for all samples of olive
oil shows a decrease of viscosity with an increase of
temperature. This behavior is attributed to the reduction in
intermolecular forces resulting from a higher thermal
movement among molecules as the temperature increases.
This makes the flow among the molecules easier and
therefore, reduces the viscosity [9]. Another point to note is
that among all temperatures studied, the difference in viscosity
between the two temperatures, 10oC and 20oC, is the largest.
On the other hand, the Newtonian behavior is observed at all
temperatures studied for all of the samples.
The effect of temperature on the shear stress of olive oil as
a function of shear rate is also shown in Fig. 1. Shear stress
increased with increasing shear rate for all types of olive oil.
At the same shear rate, shear stresses were higher at lower
temperatures. In addition, increases in shear stress with
increasing shear rate were more remarkable at lower
temperatures. From the graph it is clear that all of types of
olive oil exhibit Newtonian behavior at this range of
temperature.
Esam A. Elhefian is with Chemistry department, Faculty of science,
University of Zawia, Az Zāwīyah, Libya (e-mail: [email protected]).
37
40 deg
50 deg
100
80
60
40
20
0
0
1
2
3
2
(a)
40
2
3
20
0
0
1
2
3
Shear stress/ D cm -2
40
2
80
1.5
60
1
40
0.5
20
-2
Shear stress/D cm
15 s
30 s
45 s
60 s
15 s
30 s
45 s
60 s
Shear stress/D cm-2
Apparent viscosity/cP
100
0
2
4
4
ln η
ln η
R2 = 0.9971
5
2
R = 0.9979
3
3
2
2
1
1
0
3
3.1
3.2
3.3
3.4
3.5
3
3.6
3.1
3.2
3.3
3.4
3.5
3.6
1000/T
1000/T
(a)
(b)
R2 = 0.9988
3
2
1
0
3
3.1
3.2
3.3
3.4
3.5
3.6
1000/T
2
1.5
1
(c)
1
2
3
Fig.4 The Arrhenius plot of ln η versus 1/T for (a) fresh, (b) 1 year
and (c) 2 years olive oil (at 6.15 s-1)
4
10 deg
20 deg
25 deg
30 deg
40 deg
50 deg
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
Shear rate/s-1
1
2
3
IV. CONCLUSION
This study has shown that Newtonian behavior was
observed at temperatures from 10°C to 50°C for all types of
olive oil used. Almost no change was observed when the
effect of shearing time and storage time (until 2 years) was
studied. Finally, all types of olive oil used were found to obey
the Arrhenius equation.
4
Shear rate/s -1
(e)
(f)
Fig.1 The influence of the shear rate and temperature on the
rheological curves of (a,b) fresh , (c,d) 1 year and (e,f) 2 years olive
oils.
ACKNOWLEDGMENT
fresh
1 year
2 years
140
The author is grateful to Mr. Mahfud Abolgasim for
providing the samples.
120
100
Viscosity/cP
2.5
4
2.5
0
4
4
6
5
(d)
60
3
-1
(b)
120
6
3
(c)
80
2
Shear rate/s
(c)
Shear rate/s -1
100
1
4
4
0
10 deg
20 deg
25 deg
30 deg
40 deg
50 deg
0
0
4
Fig. 2 The influence of shearing time on the rheological curves of (a)
fresh, (b) 1 year and (c) 2 years olive oil.
10 deg
20 deg
25 deg
30 deg
40 deg
50 deg
Shear rate/s-1
120
0.5
20
15 s
30 s
45 s
60 s
15 s
30 s
45 s
60 s
Shear rate/s -1
4
3.5
4
140
1
40
0
0
0
1
3
1.5
60
0
0.5
0
Apparent viscosity/cP
3
5
20
0
2
-1
4.5
Shear stress/D cm-2
Apparent viscosity/cP
60
1
80
(a)
(b)
80
2
0
5
1
Shear rate/s
100
2.5
100
6
0
120
20
120
Shear rate/s-1
2.5
2
1.5
1
0.5
0
4
140
0.5
0
10 deg
20 deg
25 deg
30 deg
40 deg
50 deg
5
4.5
4
3.5
3
Shear rate/s -1
10 deg
20 deg
25 deg
30 deg
40 deg
50 deg
1
40
ln η
Viscosity/cP
120
1.5
60
15 s
30 s
45 s
60 s
15 s
30 s
45 s
60 s
0
Shear stress/D cm-2
10 deg
20 deg
25 deg
30 deg
2
80
0
where A is a constant related to molecular motion, Ea is the
activation energy for viscous flow at a constant shear rate, R is
the gas constant and T is the absolute temperature in K. A plot
of ln viscosity as a function of 1/T should produce a straight
line and from its slope the Ea can be calculated. Fig. 4 presents
an Arrhenius plot for the three olive oil samples. These graphs
show linear relationships.
140
2.5
100
-2
Apparent viscosity/cP
120
Shear stress/D cm
Viscosity measurements were performed as a function of
shear rate at several shearing times (15, 30, 45 and 60
seconds) at 25oC to study the shearing time effect (Fig. 2). At
all shearing times applied, all samples exhibit similar behavior
and no significant change was observed. In addition, when the
period of storage was extended to two years at a constant
shear rate, almost no change in viscosity was observed (Fig.
3).
The viscosity values obtained at a constant shear rate (6.15
s-1) can be correlated with temperature according to the
Arrhenius equation:
η = A . e-Ea/RT
(1)
Apparent viscosity/cP
International Journal of Chemical, Environmental & Biological Sciences (IJCEBS) Volume 2, Issue 1 (2014) ISSN 2320–4087 (Online)
80
60
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40
20
[1]
0
10
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40
50
Temperature/ oC
[2]
Fig. 3:The effect of storage time on the apparent viscosity
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[3]
[4]
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