JSIR 73(3) 153-156

Journal of Scientific & Industrial Research
Vol. 73, March 2014, pp. 153-156
Studies on Thermal Stability of Palm -Sesame oil blends during Deep Fat Frying
M. R. Tiwari 1*, K. K. Tiwari 1 and S. D. Toliwal2
1
Sophisticated Instrumentation Center for Applied Research & Testing (SICART), Vallabh Vidyanagar-388 120,
Anand (Gujarat), India
2
S. L. T. Institute of Engineering and Technology, Rajkot-360001 (Gujarat), India
Received 08 August 2012; revised 27 December 2013; accepted 28 January 2014
The effect of blending Palm oil (PO) with Sesame oil (SeO) in different ratios has been investigated to get blends with
low cost and better nutritional advantage relative to SeO.The blend of PO with SeO is also prepared with Saturated Acid:
Monounsaturated Acid: Polyunsaturated oil (S: M: P) in the ratios of 1:1:1 in view of its nutritional significance. Studies
were conducted on individual and blended oils to determine thermal stability at 180° C in oven for 12 hours and during
Deep Fat Frying (DFF) of dry potato chips at 180° C for 9 hours. The individual and blended oils were analyzed for
physico-chemical properties and fatty acid composition and were then used to determine the thermal stability and DFF
studies. The changes in fatty acid composition and physico-chemical characteristics of individual and blended oils at the end
12 hours for thermal stability and at the end of 9 hours for DFF studies have been reported.
Key words: Thermal stability, Deep Fat Frying, Sesame oil, Palm oil, S: M: P ratio, Fatty acid composition
Introduction
DFF is one of the oldest and most popular food
preparation methods reported by Garaya et al.1 The
economy of commercial DFF has been estimated to
be $ 6 billion year1 in USA and at least twice that
amount for rest of the world. Fried foods have a
desirable flavor, color and crispy texture which make
deep-fat fried foods very popular with consumers.2
Frying oils constitute a substantial part of human
diet. These oils not only serve as important source
of energy but also provide certain functional
characteristics to regulate a metabolic activity.
Therefore good compromise between nutritional and
thermal stability of frying oils is essential. Consumers
can offer a better quality product with respect to
flavor and nutritive value. Blending reduces the
demands for regional preferences of precise
individual oil, there by indirectly helping in
stabilizing edible oil price in a country.3
The oils can be blended even to derive protective
advantages due to the presence of explicit ingredients
that offer protection against oxidation to improve
frying recyclability.4 Over all blended oil has better
physico-chemical properties and stability against
oxidation during DFF. 5 The oxidized products of
fatty acids give off-flavors and hydrolytic rancidity to
——————
*Author for correspondence
Email: [email protected]
the frying medium and fried foods.6 PO was therefore
blended with SeO in different proportions to improve
its degradative stability, reduce cost and achieve fatty
acid composition close to ideal. SeO blended with
PO is expected to give blends rich with natural
antioxidants and delayed deteriorating tendency. The
present study has been undertaken to evaluate effect
of blending of PO with SeO on its thermal stability
during DFF.
Materials and methods
Refined PO and refined SeO were procured
from local market. PO was blended with SeO in ratio
of (80:20), (20:80) and also blended in ratio (52:48)
to achieve S: M: P ratio closes to 1:1:1. The blends
(1000gm) were prepared by mixing the oils in given
ratio (wt/wt) in 2 Liters R B flask at 60°C for
20 minutes with nitrogen bubbling and mechanical
stirring and cooled to room temperature. After
blending, the blended oils were stored in stainless
steel container under inert atmosphere a single
batch of 1 Kg potato chips was also purchased locally
in 500 gm packs. Dust and other impurities were
removed from them before deep-frying trials.
Thermal Stability Studies
100 gm of individual oils as well as their blends
were taken in 250 ml beaker and subjected to
prolonged heating for 12 hours in oven maintained at
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J SCI IND RES VOL 73 MARCH 2014
180C. The samples were cooled to room temperature
and analyzed for physico-chemical properties.
Deep-fat frying (DFF) trials
A deep fat fryer (vessel) with 1-liter capacity
was used during experiment. The fryer was filled with
300 gm of oil for frying. The temperature was set at
180C, and oil was kept heated at this temperature
throughout the 9 hours trial. In order to assess the
maximum deterioration possible in the heated oil, the
oil was not replenished at any time during experiment.
The individual oils and their blends were used
for DFF of potato chips at 180C for 9 hours. DFF
of potato chips was conducted in 30 gm batches,
at 1.50 hourly intervals. Each batch was fried for
3 minutes. Thus a total 6 batches were fried during
9 hours frying trial. After each batch of frying, an
aliquot of 30 ml of the individual and blended oils
was taken for physico-chemical tests. The recovered
oil samples were stored in food grade 100 ml plastic
bottles at room temperature away from direct sunlight
Estimation of Free Fatty Acid (FFA), Peroxide
Value (PV) and Color was carried out at 1.50 hourly
intervals and Iodine Value (IV) was determined
after every 3 hours of frying AOCS7 methods.
The Conjugated dienes content was calculated by
PORM 8 methods. Changes in fatty acid profile
of pure as well as blended oils before and after frying
were studied by Perkin Elmer Auto system XL gas
chromatograph with flame ionization detector (FID).
The capillary column BP-225 (moderate Polar,
25 meters x 0.22 mm x 0.25 microns) with 50%
Cynopropylphenyl Polysiloxane as stationary phase
was used for analysis AOCS 9 methods.
Results and discussion
Thermal Stability Studies
The initial and final values of Acid Value (AV),
IV, PV and Color are presented in Part-A and Part-B
of (Table-1) respectively. The percentage changes in
characteristics on prolonged heating of individual
oils and the blends are shown in Part C of (Table-1).
A general trend of increasing in ∆ %AV of PO, SeO
and their blends heated for 180°C for 12 hours.
The addition of 20, 52 and 80% PO to SeO increases
∆% AV to 22.85, 23.93 and 25.91% in PO, SEO and
their blends. SeO didn’t show much increase in AV as
exhibited by PO indicating its better stability to
hydrolysis relative to PO.4
There is progressive increase in ∆% PV of PO, SeO
and their blends. The addition of 80, 52 and 20% PO
to SeO shows increase in ∆%PV 7.14, 7.19 and 7.35%
in PO, SEO and their blends. It can be seen that
marginal increase in PV was observed indicating
slight oxidative deterioration. Table-1 shows changes
in ∆ % color of individual PO (11.13%) and SeO
(22.78%). Blending of PO with SeO at 80, 52 and
20% caused change in the color range from 13.79
to 19.44%. The change in color was observed more
in SeO than PO during 12 hours thermal stability.
Table-1 also shows the effect of blending on IV of oil
blends compare to individual oils. The IV of PO and
SeO is 52.50 and 111.79% respectively. The addition
of 80, 52 and 20% of PO to SeO resulted decrease
of IV 69.07, 84.66 and 93.79% for PO, SeO and
their blends. The ∆ % reduction in unsaturation
character reaches 2.67, 2.64 and 2.59% in SeO.
The marginal drop in IV indicates extent of
polymerization was least in PO, SeO and their blends.
The blend of PO52:SeO48 with S: M: P ratio
1.15:1.32:1.00 has highest thermal stability. So it
can be deduced that blend with PO52:SeO48
showed better thermal stability than SeO and better
hydrolytic than PO.
Deep Fat Frying Studies
Using PO to get blends with SeO is expected to
give blends with cost, health and performance
benefits. The chemical characteristics studied during
DFF showed steady increase in FFA for PO, SeO and
their blends between 1hr to 9hr. The initial value
of FFA of PO and SeO was 1.27% and 1.86%
respectively. The final value of FFA of PO and its
blend with SeO in ratio of 100:0, 80:20, 52:48, 20:80,
0:100 were 7.30%, 7.50%, 8.00%, 8.50% and 8.90%
respectively. The increase in FFA was found to be
more in SeO, PO: SeO blends in ratio of 52:48, 20:80
as compared to 80:20 and PO. Legislation in some
countries specifies that the AV of fat used for frying
must not exceed 2.5 (FFA 1.25). In the present study,
oils and their blends crossed this limit after 9 hours of
intermittent DFF with potato chips.
The IV data shows progressively decrease in
unsaturation in oils and their blends. It was observed
that IV of PO decreased by 4.39 units only while
in case of SeO decreased by 5.85 units after 9 hours
of drying. The IV for PO, SeO blends in ratio of
80:20, 52:48 and 20:80 after frying for 9 hours
at 180°C were reduced by respectively 4.49, 4.95
and 5.30 units. The IV of oil does not indicate the
position of the doubles or amount of olefinic carbon
but rather provided over all status of unsaturation
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TIWARI et al.: STUDIES ON THERMAL STABILITY OF PALM
Table 1—Physico-chemical Characteristics of Oils /Blend during thermal stability studies
OIL/BLEND
PART-A Initial Values
Palm Oil(PO)
PO80:SeO20
PO52:SeO48
PO20:SeO80
Sesame Oil (SeO)
PART-B Final Values
PART-C Difference
AV
IV
PV
Color
(Y +5R)
AV
IV
PV
Color
(Y +5R)
2.54
2.74
3.05
3.50
3.72
52.50
70.97
86.96
96.29
111.79
2.80
3.50
5.70
6.80
3.63
5.30
5.80
6.70
7.20
7.90
3.24
3.45
3.78
4.30
4.50
51.10
69.07
84.66
93.79
108.89
3.00
3.75
6.11
7.30
3.90
5.89
6.60
7.80
8.60
9.70
 AV
(%)
27.55
25.91
23.93
22.85
20.96
 IV
(%)
2.66
2.67
2.64
2.59
2.59
 PV
(%)
7.14
7.14
7.19
7.35
7.43
Color
(%)
11.13
13.79
16.41
19.44
22.78
Table 2—Effect of frying on fatty acid compositions of frying oils and their blends
Fatty Acid
Palm Oil (PO)
Before
After
16:00
46.58 50.42
16:01
--18:00
4.21
4.90
18:01
37.83 38.68
18:02
9.37
4.52
18:03
2.01
1.48
% SFA
50.79 55.32
% MUFA
37.83 38.68
% PUFA
11.38
6.00
Loss (% Wt of fatty acid after 9
hours)
PO:SeO (80:20)
Cal
46.58
-4.52
35.73
4.17
1.36
51.10
35.73
5.53
-7.64
Before After
38.01
-4.39
38.60
16.88
2.12
42.40
38.60
19.00
41.51
-5.15
39.85
11.93
1.56
45.90
39.85
13.49
PO:SeO(52:48)
Cal
Before After
Cal
38.01
-4.71
36.48
10.92
1.42
42.72
36.48
12.34
28.61 31.45
--4.55
5.20
38.04 38.89
26.52 22.96
2.28
1.50
33.16 36.65
38.04 38.89
28.80 24.46
28.61
-4.73
35.37
20.88
1.36
33.34
35.37
22.24
-8.46
of the oils. So it is not possible to point out the
position of double bond(s) which are more susceptible
to oxidation.10
The PV was 5.50 units for PO where as
8.40 units for SeO after 9 hours of frying. The PV for
PO, SeO blends in ratio of 80:20, 52:48, 20:80 were
6.90, 7.80 and 8.00 units respectively. PV increased
gradually in PO, SeO and their blends. PV increase
was least for PO and highest for SeO indicating
highest and lowest oxidative stability respectively for
PO and SeO clearly due to more tecopherol and
tocotrienol content in PO.11 The color of PO, SeO and
their blends increased on continuous heating for
9 hours during DFF. The color was least in PO and
increased with increase in conc. of SeO in blends.
An increase in the color intensity is due to the
accumulation of non- volatile decomposed compounds
such as oxidized triacylglycerol and FFA.
The percentage fatty acid composition of the
oils before and after the 9 hours frying trials is given
in (Table 2). It was observed that the loss in
Unsaturated Fatty Acid (USFA) was 8.89 % in SeO
frying and 7.64 in PO frying. The loss decreased
from 9.00 % in 20:80 blend of PO:SeO to 8.46%
in 80:20 blend of PO:SeO after 9 hours of heating
-9.05
PO:SeO (20:80)
Before After
17.82
-4.78
37.40
37.65
2.35
22.60
37.40
40.00
19.58
-5.16
38.93
35.00
1.33
24.74
38.93
36.33
Cal
17.82
-4.69
35.43
31.85
1.21
22.51
35.43
33.06
-9.00
Sesame Oil (SeO)
Before After
12.83
-4.90
37.83
42.36
2.08
17.73
37.83
44.44
14.08
-6.05
40.82
37.61
1.44
20.13
40.82
39.05
Cal
12.38
-5.51
37.19
34.27
1.31
17.89
37.19
35.58
-8.89
with intermittent DFF. SeO showed slight loss of
USFA than PO. A slight increase in conjugated dienes
was observed after 9 hours of frying for SeO and PO
and their blends indicating some degree of primary
oxidation. Similar finding had been reported earlier
by Singh et al. 12-13
Conclusions
It can be concluded that the blends of PO with SeO
in different proportions are more stable to oxidative
deterioration due to heating as compared to SeO.
Addition of PO to the SeO means longer frying times
for the latter, and could make the PO acceptable to the
consumers who prefer foods with aroma and flavour
imparted by SeO. The protection afforded by PO to
SeO increased with increase in proportion of PO in
blends. Apart from protection advantage blend with
PO52:SeO48 due to ideal fatty composition of 1:1:1
of SUFA: MUFA: PUFA offers nutritional advantage
as frying medium. The blending of the oils improves
and enhances the nutritional and functional qualities
of the oils by combining thetwo oils into one and
accordingly improved commercial viability. Meanwhile,
the presence of different kinds of natural antioxidants
in oil blends confers synergistic effect to the blend.
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J SCI IND RES VOL 73 MARCH 2014
Acknowledgement
Authors are thankful to Director, SICART, Vallabh
Vidyanagar for providing sophisticated analytical
instrumentation facility and take keen interest in these
studies.
6
7
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