Food and Nutrition Sciences, 2010, 1, 24-29
Published Online July 2010 (http://www.SciRP.org/journal/fns)
1
Effects of Mixing Canola and Palm Oils with Sunflower Oil on
the Formation of Trans Fatty Acids during Frying
Radwan S. Farag1, Magdy A. S. El-Agaimy2, Bothaina S. Abd El Hakeem3
1Department of Biochemistry, Faculty of Agriculture, Cairo University, Giza, Egypt; 2Department of Fats & Oils, Food Technology
Research Institute, Agriculture Research Centre, Giza, Egypt; 3Special Food and Nutrition Department, Food Technology Research
Institute, Agriculture Research Centre, Giza, Egypt.
Received June 7th, 2010; revised July 5th, 2010; accepted July 8th, 2010.
ABSTRACT
GLC analysis was conducted to indicate the formation of trans- C18 fatty acids of sunflower, ca nola a nd palm oils du r-
ing frying. Blends of sunflower oil and palm oil or canola oil were obtained by mixing sunflower oil with palm or ca-
nola oils at the volume ratios of 60: 40, 40: 60 and 20: 80 (v/v), then heated at 180˚C ± 5˚C for 5, 10, 15 and 20 h in the
atmospheric oxygen. GLC results demonstrate that the formation of trans C18-fatty acids was generally dependent
upon the frying time and oil mixing ratios. Furthermore, mixing sunflower oil with oils rich in monounsaturated fatty
acids (palm or canola oils) lowered the formation of trans-C18 fatty acids during frying.
Keywords: Sunflower Oil, Canola Oil, Palm Oil, Trans Fatty Acids, Frying Process, GLC Analysis
1. Introduction
Trans fats or trans fatty acids are unsaturated fatty acids
with at least one double bond in the trans configuration.
Trans fatty acids occur naturally in small amounts in
foods produced from ruminant animals. However, most
of trans fatty acids in the diet are produced during the
process of partial hydrogenation of vegetable oils into
semi-solid fats [1]. Also, trans-fatty acids can be formed
from cis-unsaturated fatty acids by the effect of several
bacteria, especially parasitic bacteria in the rumen of
cattle which convert unsaturated lipids from cis to
trans-isomers through a cis/trans isomerase [2].
Trans fatty acids have an adverse effect on blood lip-
ids and have been shown to increase the risk of heart
disease. Trans fatty acids increase LDL-cholesterol (the
bad cholesterol) and decrease HDL-cholesterol (the good
cholesterol) and overall, trans fatty acids increase LDL
cholesterol (bad cholesterol) similarly to saturated fat,
but, unlike saturated fat, they also decrease HDL choles-
terol. As a result, the net effect of trans fat on the
LDL/HDL cholesterol ratio is approximately double that
of saturated fat. It is worth noting that the risk of cardio-
vascular disease is increased if trans fatty acids are con-
sumed in high amounts [1,3]. In addition, trans fatty ac-
ids appear to have an adverse effect on some lipoproteins
and apoproteins when fed at relatively high levels [4]. In
contrast, lower levels of trans fatty acids did not appear
to be deleterious [5].
Deep-fat frying is one of the most processes used in all
food preparations. Basically, this process includes im-
mersing a food item in a large quantity of heated oil and
reused several times before being disposed. Deep-fat
frying produces a product with desired sensory charac-
teristics, including fried food flavour, golden brown col-
our and a crisp texture [6]. This process has also been
considered a source for the production of trans fatty ac-
ids. Formation of trans fatty acids during frying has been
shown to be closely related to process temperature and
time. In sunflower oil, the amount of trans isomers were
found to be 1.10 % when heated at 200˚C for 40 min as
compared to 11.45% at 300˚C for the same duration of
heating [7]. Conversely, Romero et al., [8] reported a
very minimal production of eliadic acid in extra virgin
olive oil, high oleic sunflower oil and sunflower oil. On
the other hand, commercial frying and baking oils con-
tain significant amount of trans fatty acids. In general,
baked goods, fries snack foods (e.g., dough nuts, French
fries) and fried fast-food items (e.g., fried chicken and
fried fish) contain significant amounts of trans fatty acids
[9].
It seems that cis/trans-isomerisation process depends
on the most prominent fatty acids present in an oil. For
instance, eliadic acid was the most abundant trans fatty
acid in extra virgin olive oil fried potatoes while trans
linoleic isomers were more abundant in sunflower oil.
High oleic sunflower oil was in between [8].

Effects of Mixing Canola and Palm Oils with Sunflower Oil on the Formation of Trans Fatty Acids during Frying
25
In this context, the Food and Drug Administration
(FDA) [10] ruled that the nutrition labels for all conven-
tional foods and supplements must indicate the content of
trans fatty acids. In addition, the Department of Agricul-
ture made a limited intake of trans fatty acids a key
recommendation of the new food-pyramid guideline
subsequent to the recommendations of the Dietary
Guidelines Advisory Committee [11] that the consump-
tion of trans fatty acids be kept below 1% of total energy
intake. Furthermore, the UK Faculty of Public Health
and Royal Society for Public Health [12] proposed that
consumption of trans fatty acids should be virtually
eliminated.
A set of experiments was conducted in the present
study where oils rich in monosaturated fatty acids (ca-
nola and palm oils) were mixed with sunflower oil at
various volume ratios in an attempt to extent its shelf-life
[13]. The major objective of the present work was to see
if blending oils rich in monosaturated fatty acids with
sunflower oil might lower the formation of trans fatty
acid content of the binary oil blends during frying at
180˚C for 5 h daily for 4 consecutive days.
2. Materials and Methods
2.1 Oils
1) Refined sunflower oil was obtained from Sila Edible
Oil company (Kom Osheim, El-Fayoum governorate, Egypt).
The oil peroxide and acid values were 1.2 (meq. active
oxygen Kg⎯¹ oil) and 0.08 (mg KOH/g⎯¹ oil), respectively.
2) Refined palm oil was obtained from Savola Sime
company, 10th of Ramdan city , Sharkia governarate,
Egypt . The oil peroxide and acid values were 0.14 (meq.
active oxygen Kg⎯¹ oil) and 0.043 (mg KOH g⎯¹ oil),
respectively.
3) Canola seeds (Brassica species, Serwi 4 variety)
were obtained from Oil Crops Department, Field Crops
Research Institute, Agriculture Research Centre, Ministry
of Agriculture, Giza, Egypt. The seeds were ground and
packed in cheese cloth, pressed by hydraulic Carver
(model 2759 S/N 2759-584 Freds. Carver Inc., U.S.A.).
The produced oil was filtered through Whatman filter
paper No.1 and kept in a brown glass bottle at 7˚C.
2.2 Frying Process
A known amount (2 L) of each of refined sunflower,
palm and canola oils were separately placed in a Cordon
Bleu deep fat-fryer (Model DZ-05D, China) equipped
with a temperature controller. Portions of sunflower oil
were mixed with palm oil or canola oil at ratios of 60: 40,
40:60 and 20: 80, (v/v). Potato chips (2 mm thickness ×
40 mm width × 50 mm length ) were soaked in a sodium
chloride solution ( 10%, w/v ) for 0.5 h and fried in dif-
ferent oil samples at 180ºC ± 5ºC. The frying process
was conducted 4 times each day and the frying period
was 5 h day⎯¹. This process was repeated for 4 consecu-
tive days. Oil samples were taken every 5 h and the total
continuous heating period was 20 h. The oil samples
were left to cool down then stored at – 10ºC for fatty acid
analysis.
2.3 Fatty Acid Compositions of Fried Sunflower,
Palm and Canola Oils and Their Binary
Mixtures
Capillary gas chromatography (HP 6890) was used for
the qualitative and quantitative determinations of fatty
acids of the oil samples and reported in relative area per-
centages. Fatty acids were transesterified into their cor-
responding fatty acid methyl esters (FAMEs) by shaking
a solution of oil (ca. 0.1 g) in heptane (2 ml) with a solu-
tion of methanolic potassium hydroxide (0.2 ml, 2N).
The FAMEs were identified using a gas chromatograph
equipped with DB-23 (50%- cyano propyl)-methylpoly
siloxane) capillary column (60m × 0.32 mm × 0.25 µm
film thickness) and a flame ionization detector. Nitrogen
flow rate was 0.6 ml/min, hydrogen and air-flow rates
were 45 and, 450 ml/min, respectively. The oven tem-
perature was isothermally heated at 195˚C. The injector
and the detector temperatures were 230˚C and 250˚C,
respectively. MEFAs were identified by comparing their
retention times with known fatty acid standard mixture.
Peak areas were automatically computed by an integrator.
All GC measurements for each oil sample were made in
triplicate and the average values were reported.
3. Results and Discussion
3.1 Trans C18 Fatty Acids of Individual Oils
In this set of experiments, the major concern is focused
on the formation of trans-fatty acids (eliadization) during
heating at 180˚C ± 5˚C for various periods. It is worth
mentioning that the fatty acid profile of fresh sunflower
oil was discussed earlier in detail [13]. Tabl e 1 shows the
changes in heated sunflower oil during frying. No
trans-oleic acid (elaidic) was found after the first 5 h
heating period. Afterwards, its content was slightly and
gradually increased towards the end of heating period
(20 h). Similar results were noticed with trans linoleic
acid (linoelaideic acid). It is worth mentioning that the
amount of trans linoleic acid was much greater than that
of trans-oleic acid (Figure 1). Similar findings were re-
ported by Hunter and Applewhite [9] who reported that
the trans amounts of fatty acids increased gradually by
increasing the heating period.
Looking at trans fatty acid profile of heated palm oil at
180˚C ± 5˚C for various periods, one can deduce the fol-
lowing remarks. The amount of trans-oleic acid was
formed at 5 h and its amount become constant throughout
the entire heating period (20 h). It is worth mentioning
that the amount of trans-oleic acid was much lower than

Effects of Mixing Canola and Palm Oils with Sunflower Oil on the Formation of Trans Fatty Acids during Frying 26
Table 1. Trans and their parent fatty acid compositions (area %) of heated sunflower, palm and canola oils for various peri-
ods
Heating period (h)
20 15 10 5 20 15 10 5
Oil blend
Cis-oleic acid Trans-oleic acid (elaidic) acid
29.22 29.13 28.33 29.16 0.15 0.13 0.03 ND Sunflower oil
41.20 39.57 39.58 40.25 0.05 0.04 0.04 0.03 Palm oil
49.14 47.15 46.71 46.25 0.14 0.11 0.06 0.03 Canola oil
Cis-linoleic acid Trans-linoleic (linolaidic) acid
55.42 56.40 57.99 57.52 1.5 1.22 1.09 ND Sunflower oil
9.31 9.40 10.20 12.09 0.09 0.08 0.08 0.08 Palm oil
16.41 17.88 17.76 18.33 0.05 0.05 0.05 0.02 Canola oil
Total trans C18 fatty acids
1.65 1.35 1.12 ND Sunflower oil
0.14 0.12 0.12 0.11 Palm oil
0.19 0.16 0.11 0.14 Canola oil
ND refers to non detected fatty acid
Figure 1. Trans fatty acids of sunflower, palm and canola
oils heated for various periods. t- 18: 1 and t- 18: 2 acids refer
to trans-oleic and trans-linoleic fatty acids, respectively
that found in sunflower oil. However, palm oil contains
high level of oleic acid (parent acid) than that of sun-
flower oil. On the contrary, the level of linoleic acid in
sunflower oil was much greater than that present in palm
oil and the level of trans linoleic acid was about 16 times
as great as that present in palm oil at the end heating
period (20 h) (Table 1).
Dealing with canola oil, the amount of trans-oleic was
found after heating for 5 h and gradually increased
throughout at the entire heating period (20 h). The
amount of trans-oleic acid at the end of the heating pe-
riod was about the same as that of sunflower oil. The
amount of trans oleic acid increased in the following
order depending on the oil type: sunflower oil > canola
oil > palm oil. This sequence may be stem from the
level of cis-oleic which can be arranged in the following
order: according to oil type: canola oil > palm oil >
sunflower oil.
The amount of trans-linoleic acid in canola oil was
very low compared with trans-oleic of other two oils
during the various heating periods. This may be due the
low level of cis-linoleic acid compared with cis-oleic ac-
id.
In general, the total amounts of trans C18 fatty acids at
the end of this series of experiments can be arranged in
the following order: sunflower oil > canola oil > palm
oil. These findings are in contrast with the results of the
nutritional experiments reported by Farag et al., [13]
where the major alteration induced to rat organ tissues
(liver, kidney, heart) when rats administered the heated
sunflower oil, palm oil and canola oil as part of their diet.
The changes on rat organ tissues were related to the type
of fatty acids (erucic acid in canola oil and palmitic acid
in palm oil). Several reports indicated that trans acids
induced deleterious effects on human health [14]. This
fact was not found in the present work. This is might be
due to the presence of trans-acids in very low amounts
(lower than 2% in sunflower oil and 0.2% in canola and
palm oils). Similar results were reported by Nestel et al.
[5].
3.2 Trans Fatty Acids of Sunflower Oil
and Canola Oil Blends
Table 2 shows the effect of blending different ratios of
canola oil with sunflower oil and heated for various
periods. Generally speaking, the levels of elaidic in-
creased with increasing the heating period and mixing

Effects of Mixing Canola and Palm Oils with Sunflower Oil on the Formation of Trans Fatty Acids during Frying
27
1
1
1111
222222
333333
44 4444
0
0.4
0.8
1.2
1.6
2
2.4
2.8
T
ransfatty aci d s (Area%)
Fry ing tim e ( da y )
t- 18:1
t- 18:2
t- 18:1
t- 18:2
t
-
18
:
2
t-18:1
S+C (60:40, v/v)
S+C
S+C (20:80, v/v)
1= 5 h heating period
2= 10 h heating period
3= 15 h heating period
4= 20 h heating period
Figure 2. Trans fatty acids of fried sunflower oil (S) mixed
with various levels of canola oil (C) heated for different
periods. t- 18: 1 and t- 18: 2 indicate trans-oleic and trans-
linoleic acids, respectively
ratios. In the mean time, the level of cis-oleic was
slightly increased with heating time. It is noticeable that
its amount increased by increasing the blending ratio and
in particular at the volume ratio of 20:80 (v/v) (Figure
2).
Here again, the amount of trans-linoleic increased at
all volume ratios with prolonging the heating period. On
the contrary, its level was progressively decreased with
increasing the blending ratios. Concerning cis-linoleic
acid, its levels were remarkably decreased with extend-
ing the heating period and increasing with increasing the
level of canola in the blending ratios. The results with the
total trans-oleic and linoleic acids are greed quite well
with the previous findings (Table 2, and Figure 2).
3.3 Trans Fatty Acids of Sunflower Oil and
Palm Oil Blends
The amounts of trans-oleic acid and its parent acid of
heated sunflower oil and mixed with heated palm oil at
volume ratio of 60: 40 (v/v) for various periods are shown
in Table 3. In general, the results demonstrate a progress-
sive increase in the amount of elaidic with prolonging the
heating period. The amount of linolaidic acid formation
was more pronounced than that of elaidic acid with
Table 2. Trans and their parent fatty acid compositions (area %) of heated binary mixtures of sunflower oil (S) and c anola oil
(C) for various periods
Heating period (h)
20 15 10 5 20 15 10 5
Oil blend
Cis-oleic acid Trans-oleic acid (elaidic) acid
33.61 34.61 34.5633.89 0.14 0.04 ND ND S + C (60: 40, v/v)
43.57 42.59 43.0740.74 0.20 0.12 0.05 0.05 S + C (40: 60, v/v)
42.47 42.49 42.5042.19 0.40 0.26 0.11 0.07 S + C (20: 80, v/v) Cis-linoleic acid Trans-linoleic (linolaidic) acid
42.42 44.91 45.8947.89 1.60 0.92 0.90 0.80 S + C (60: 40, v/v)
29.74 31.78 32.1434.65 0.98 0.90 0.54 0.52 S + C (40: 60, v/v)
24.81 26.65 27.3527.22 0.52 0.49 0.48 0.31 S + C (20: 80, v/v)
Total trans fatty acids
1.74 0.96 0.90 0.80 S + C (60: 40, v/v)
1.38 1.16 0.65 0.59 S + C (40: 60, v/v)
0.72 0.61 0.53 0.36 S + C (20: 80, v/v)
ND refers to non detected fatty acid
Table 3. Trans and their parent fatty acid compositions (are a %) of heated binary mixtures of sunflower oil (S) and palm oil
(P) for different periods
Heating period (h)
20 15 10 5 20 15 10 5
Oil blend
Cis-oleic acid Trans-oleic acid (elaidic) acid
32.98 32.40 31.48 31.80 0.13 0.09 0.04 0.03 S + P (60: 40, v/v)
34.96 34.77 34.80 33.64 0.20 0.18 0.05 0.03 S + P (40: 60, v/v)
34.40 34.85 34.91 35.36 0.48 0.21 0.05 0.04 S + P (20: 80, v/v)
Cis-linoleic acid Trans-linoleic (linolaidic) acid
34.96 35.71 38.28 37.19 0.92 0.90 0.79 0.77 S + P (60: 40, v/v)
17.17 23.19 26.54 28.96 0.73 0.64 0.54 0.53 S + P (40: 60, v/v)
15.38 16.14 18.77 19.19 0.40 0.36 0.33 0.33 S + P (20: 80, v/v)
Total trans C18 fatty acids
1.05 0.99 0.83 0.80 S + P (60: 40, v/v)
0.93 0.82 0.61 0.56 S + P (40: 60, v/v)
0.88 0.57 0.38 0.37 S + P (20: 80, v/v)
S+C (40:60, v/v)

Effects of Mixing Canola and Palm Oils with Sunflower Oil on the Formation of Trans Fatty Acids during Frying 28
11111 1
222
222
33 333344 4444
0
0.4
0.8
1.2
1.6
2
2.4
2.8
Transfatty acids (A rea
%)
Frying time (d ay)
t- 18:1
t- 18:2
t- 18:1
t- 18:2
t- 18:1t-18:2
S+P (60:40, v/v)S+P ( 40:60, v/v
) S+P (20:80, v/v )
1= 5 h h eating per iod
2= 10 h hea ting p erio d
3= 15 h hea ting p erio d
4= 20 h hea ting p erio d
Figure 3. Trans fatty acids of fried sunflower oil (S) mixed
with various levels of palm oil (P) heated for different peri-
ods. t- 18:1 and t- 18:2 indicate trans-oleic and trans-
linoleic acids, respectively
increasing the heating time (Figure 3). This might be due
to the fact that the amount of cis-linoleic is higher than
cis-oleic acid. Also, one has to mention that cis-linoleic
acid is much labile than cis-oleic acid and rate of stero-
mutation is in the favour of linoleic acid.
With increasing the mixing ratios of heated palm oil
with heated sunflower oil (60: 40 and 20: 80, v/v) led to
an increase of the amount of elaidic acid. It is worth
mentioning that the levels of cis-oleic acid slightly in-
creased with increasing the ratio of blending palm oil
with sunflower oil. On the contrary, the level of li-
nolaidic acid decreased with increasing the admixture
ratios of palm oil (Figure 3). This is logic since the amount
of cis-18: 2 was decreased with the admixture ratio.
The results in Table 3 indicate that the amount of total
trans C18-fatty acids decreased with increasing the vol-
ume ratio of palm oil with sunflower oil during frying.
Similar findings were seen by the increasing the mixing
of canola oil with sunflower oil during frying. These
findings led to deduce that mixing sunflower oil with
canola or palm oils induced lowering effect on the to-
tal-trans fatty acids during frying. In this case one would
say mixing sunflower oil with other oils rich in monoun-
saturated acid might reduce the formation of trans fatty
acids during frying which is in the favor of human health.
The ratio of linoleic acid to palmitic acid (C18: 2/C16:
0) has been suggested by Normand et al., [15] as a valid
indicator of the level of polyunsaturated fatty acid dete-
rioration. The results of the present work showed a de-
crease in this ratio from 9.02 to 6.79, 3.82 to 2.93 and
0.24 to 0.22 at the end frying period for sunflower, ca-
nola and palm oils respectively. The ratios indicate the
incidence of deterioration of polyunsaturated fatty acids
of the oils under frying process.
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