Post on 31-Jan-2023
EVALUATION OF CHEMICAL CHANGES IN DIFFERENT
COMMERCIAL OILS DURING REPEATEDLY FRYING OF
COOKED OILS
K. KAVITHA*, G.R .YOGESWARI and T.SHANMUGA SUNDARAM
1. Department Of Biochemistry, Government Arts College, Paramakudi, Tamilnadu, India
2. Department of Biochemistry and Biotechnology, Annamalai University Chidambaram,
Tamilnadu India
Abstract
In this present study was changes in chemical parameters repeatedly used cooked
frying different oil samples, such as Sunflower oil, Palm oil and Groundnut oil. Evaluation of
acid number, iodine number, saponification number and peroxide number for repeatedly
cooked frying oils to all three samples. The acid value of the frying oil increases with reused
frying oil. The acid value of the frying oils were found to increase from 0.302 to 0.7728 in
Sunflower oil, 0.336 to 1.03 in Palm oil and 0.344 to 1.002 in groundnut oil. This result
indicates that acid value increased during reused frying times. Saponification values results
indicate that cooking oils were reused for frying vegetables or foods the saponification value
was changes. Peroxide value was measured for all type of oils. This result indicate that
rancidity reaction have occurred during storage it could be used as an indication of the
quality and stability of oils. Sunflower oil had highest peroxide value among 3 types of
cooking / edible oils. Separation of oil sample using by TLC method. In this experiment
showed results fresh oil has high Rf value and third time used frying oil had lowest Rf value
due to degradation of oil during heating. The result of FTIR study indicated a pronounce
difference between control and repeatedly used frying Sunflower oil samples. Sample 1 fresh
sunflower oil the FTIR spectra exhibited a peak 3685CM-1 denote O-H stretching alcohol
groups in lipids. Sample 1 FTIR spectra has total 16 frequency functional group present in
fresh sunflower oil. Second time cooked frying oil has 15 frequency and their functional
groups present in oil sample. This oil sample was second time cooked frying oil contain new
functional group found in this oil sample. The peak value of 1102CM-1 indicate of amine
functional group. These amine group was present in edible oil gives toxic into human health.
The total 19 peaks value were present in second time cooked frying oil. Sample 4 FTIR
spectra revealed 16 peak values. The peak values of 1236CM-1 and 1103CM-1 were indicated
the presence of C-N stretching group. Which is obtained in edible oil gives toxic into human
health. Hence these results indicated that we should avoided repeatedly used cooking oil for
deep fried foods.
Keywords: FTIR, TLC Peroxide Number, Iodine Number, Saponification Number
*Corresponding Author:
Ms K. Kavitha, Department of Biochemistry, Govt. arts college Paramakudi Tamil nadu ,
India Email: biokavi2011@gmail.com
Journal of Information and Computational Science
Volume 10 Issue 1 - 2020
ISSN: 1548-7741
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Introduction
Fat is one of the three main macronutrients, along with the other two: carbohydrate
and protein. Fats molecules consist of primarily carbon and hydrogen atoms, thus they are all
hydrocarbon molecules. “Partially hydrogenated vegetable oil” is a term often found on food
ingredient labels. It means that some of the fatty acids in the oil were “hydrogenated”
(reduced, so that the double bonds were converted to single bonds). Saturated fat and
monounsaturated fat form solids at room temperature. Polyunsaturated fat is (usually) liquid
at room temperature (Stier F S, 2004).
Lipid oxidation generates volatile and non-volatile compounds that interfere in taste
and flavour. The volatiles in the frying oil increase at the beginning of the process, but
decrease during the frying. There are volatiles important to the quality of the process, such as
saturated aldehydes C6-C9, enals (e.g., 2-decenal), dienals (e.g., 2, 4-heptadienal), and
hydrocarbons (hexane, heptane, octane, nonane, and decane). The formation of non-volatile
decomposition products is due to the oxidation and polymerization of unsaturated fat acid.
Aldehydes affectthe flavour of deep-fried foods, as 2-Trans-4-trans-decadienal that
contributes to a flavour while other aldehydes produce off flavour (Boskou D. et al., 2002).
Deep-fat frying is one of the oldest and popular food preparations. The economy of
commercial deep-fat frying has been estimated to be $83 billion in the United States and at
least twice the amount for the rest of the world (Pedreschi and others 2005). Frying is a
process of immersing food in hot oil with a contact among oil, air, and food at a high
temperature of 150 ◦C to 190 ◦C.
Deep frying consists of submerging foods in a high-temperature fatty medium, normally oil,
until cooked to the desired taste and texture. Through this process, foods absorb a notable
amount of fat and, consequently, accumulate a certain proportion of degraded products from
the fatty medium (Marcano J, et al 2010). Frying occur sat high temperatures and in the
presence of air, moisture, and the food itself; these conditions mean that the fats/oils used for
frying are subject to various alterations, such as hydrolysis and thermos oxidation. The
process of frying also results in the degradation of numerous compounds including free fatty
acids, hydro peroxides, mono acyl glycerides, di acyl glycerides, cyclic/geometric isomers of
unsaturated fatty acids, and of oxidized tri acyl glyceride monomers, dimers, and oligomers
(Tabee E, et al 2009). In the present study, an attempt has been made to evaluate changes in
chemical properties of oil during different times, cooked frying oil.
Materials and Methods
Collection of Sample:
Three different a commercial oils sample (Sunflower, Palm, Groundnut) were
collected from local market at paramakudi.
Journal of Information and Computational Science
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Collection of Frying Oil Sample:
Three types of cooking oils (Sunflower, Palm, Ground nut) each oils were subjected
to first time, second time, third times of frying and it was taken as samples for quality
analysis.All heated samples were cooled at room temperature and then stored until chemical
analysis.
Determination of Acid Number:
The acid number of a fat is the number of milligram of potassium hydroxide required
to hydrolyse the free fatty acid present in 1 gm of fat.
During storage fats become rancid as a result of peroxide formation at the double
bonds by atomic oxygen or may be hydrolysed by microorganisms due to the liberation of
free fatty acids. The amount of free fatty acids present gives an indication of the age and
quality of fat.
Determination of Saponification Value
The saponification value of an oil is defined as the number of milligrams of KOH required to
hydrolyse 1gm of oil or fat. Oils and fats are triesters of glycerol with long chain organic
acids. These triesters are hydrolysed in the presence of an alkali (KOH).
Determination of Peroxide Value of Oil Samples
Peroxide value is a measure of the peroxides contained in the oil. The peroxides present are
determined by titration against thiosulphate in the presence of potassium iodide. Starch is
used as indicator.
Determination of Iodine Number
Iodine number is defined as the number of grams of iodine taken up by 100g of oil or
fat. In this case, addition reaction takes place across the double bonds of unsaturated fatty
acids present in the fat by the addition of a halogen, such as iodine. Thus, the iodine number
gives the indication of the degree of unsaturation of fats. Iodine value is directly proportional
to the degree of unsaturation. Determination of iodine number is used for the assessment of
this purity. In Hanu’s method, the oil is treated with Hanu’s reagent. (Iodine bromide in
chloroform) for a period of time. The unreacted iodine is titrated against standardized
thiosulphate solution.
Thin Layer Chromatography
Saturated and unsaturated long chain fatty acids are basic structural elements of lipids.
Therefore , chromatographic determination of fatty acids composition by TLC for analysis of
cooked oils.
Fourier Transform Infrared Spectroscopy (FTIR) analysis
FTIR is most useful for identifying chemicals that are either organic or inorganic.
Journal of Information and Computational Science
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It can be utilized to quantitative some components of an unknown mixture and for the
analysis of solids,liquids, and gases. The term Fourier Transform Infrared Spectroscopy
(FTIR) refers to a development in the manner in which the data is collected and converted
from an interference pattern to a spectrum. It is a powerful tool for identifying types of
chemical bonds in a molecule by producing an infrared absorption spectrum that is like a
molecular "fingerprint". The wavelength of light absorbed is characteristic of the chemical
bond as can be seen in this annotated spectrum.
FTIR spectra of oil samples three times cooked frying oils were recorded with the
help of a Fourier Transformation Spectroscopy. It is used to study the saturation and
unsaturation composition of heated oils at room temperature for monitoring the oxidation
process in oils.
Results and Discussion
The quality of sunflower groundnut and palm oils were analyzed by evaluating chemical
properties such as acid value, iodine value, saponification value and peroxide value. Results
are presented in table 1 oils with lower values of all parameters are highly appreciable to
consumers. In order to design an advanced technological process these properties are very
important parameters. the effect of temperature on these properties and the influences of
frying three times with homemade cooked food to their respective boiling points using the
same oils were also studied and results are tabulated in table 2.
Table 1 chemical properties of oils at room temperature 35ᵒC (with out heating)
Properties sunflower oil palm oil groundnut oil
Acid value (mg/KOH/g) 0.302 0.336 0.344
Iodine value (g) 132.45 58.41 136.45
Saponification (mg) 134.83 121.20 188.19
Peroxide value (meq/kg) 0.33 1.2 0.446
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Table 2 Evaluation of chemical parameters of three different oils at boiling point with
frying the food three times using the same oils
Trails at Acid value Iodine value Saponification Peroxide value
Boiling point ( mg/KOH/g) (g) (mg) (meq/kg)
Sunflower oil (b.p. 140ᵒC)
1st frying 0.369 125.43 131.80 6.8
2nd frying 0.571 118.47 128.77 7.2
3rd frying 0.772 111.38 124.23 8.1
Palm oil
1st frying 0.56 58.23 115.14 2.3
2nd frying 0.728 56.41 112.11 2.8
3rd frying 1.03 54.01 110.60 3.3
Ground nut oil
1st frying 0.672 133.41 155.14 3.2
2nd frying 0.888 130.01 146.50 3.6
3rd frying 1.002 128.04 140.05 4.2
Table 2 shows that all chemical parameters are highly variable value between 1st time frying
oils and 3rd time using frying oils.
Acid Value
The acidity of oil is due to hydrolysis or oxidation of oil by atmospheric moisture leading to
the formation of fatty acids.The milligrams of KOH required to completely neutralize free
acid present in 1g of oils is known as acid value.The acid value of the frying oils were found
to increase from 0.302 to 0.7728 in sunflower oils, 0.336 to 1.03 in palm oil and 0.344 to
1.002 in groundnut oil. Acid value increases with increased number of frying times regardless
of the type of oil.acid value indicates that 47% hydrolysed of palm oil then 40% hydrolysed
of sunflower oil and 33% of ground nut oil hydrolysed of fatty acids.
Journal of Information and Computational Science
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Iodine value
The iodine value (IV) of oil is a direct representation of the degree of unsaturation of
the oil. Iodine is used to halogenate the double bonds present in unsaturated fatty acids. This
unsaturation is in the form of double bonds which react with iodine compounds. The higher
the iodine value the more unsaturated fatty acids bonds are present in a fat (Asuque et al
2012). Table 2 shows that measured iodine values for first time to third time used frying
sunflower oils were 111.38g, 118.47g and 125.43 g respectively.
Saponification value
The larger saponification no. the better soap making ability of the oil. Higher SV for
triglycerides indicates higher medium chain fatty acids. SV for unrefined vegetables oils may
also be affected by the compounds in the nonsaponifiable fraction. Saponification value (SV)
is an index of average molecular mass of fatty acid in the oil sample (Denniston et al 2004).
The SV obtained for the three times used cooking oil samples in table 2 showed decrease
value from 1st frying oil to 3rd frying oil for all cooking oils. Highest value after 3rd times used
frying oil was obtained in ground nut oil (SD ±6.182) and lowest value was obtained in palm
oil (SD±1.887).
Peroxide value
Peroxide value (PV) is used as a measure of the extent to which rancidity reactions have
occurred during storage it could be used as an indication of the quality and stability of fats
and oils . (Ekwu and Nwagu, 2004). The peroxide value was also found to increase with the
storage time, temperature and contact with air of the oil samples. The PV values tabulated in
table 1 and table 2 for three oils range from low values to high values. Results show that the
peroxide values for sunflower oil increased from 0.33 (35ᵒC) to 8.1 (140ᵒC) third frying oil.
Peroxide value for palm oil was observed from 1.2 (35ᵒC without heating) to 3.3 (140ᵒC
boiling point ) third time used frying oil.PV values for groundnut oil was observed from
0.446 (35ᵒC fresh ) to 4.2 (140ᵒC boiling point) third time used frying oil. The PV results
indicate that the PV was found to have occurred lower value which indicates a relatively good
quality of these oils. The peroxide value determines the extent to which the oil has undergone
rancidity. Peroxide value ranges are closely related to the standared value of 10 meq/kg
specified by SON, 2000, NIS, 1992.
Thin Layer Chromatography
In this experiment, 7 different oils were analysed by using TLC method. The Rf value
can be used to identify compounds due to their uniqueness to each compound. Fresh
Groundnut oil Figure 1 showed that the retention factor is 0.94 and also nine different lipids
were presented in this oil. First time using frying oil showed that the Rf value is 0.92 and
second time repeatedly using frying oil is 0.78 and third time using frying oil revealed that
the Rf value is 0.64. Repeatedly using frying oil showed that Rf value does fall from fresh oil
Rf value.
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Figure 1 Ground nut oils Figure 2 Palm oils
Figure 3 Sunflower oils
Figure 2 TLC result indicates that the fresh Pam oil value of Retention factor was
0.95. First time cooked frying oil showed the Rf value was 0.85. Second time cooked frying
oil showed the Rf value was 0.78 and third time cooked frying oil showed the Rf value was
0.64. Hence, this results indicate that degradation of lipids during reused cooking oil, showed
fall the Rf value. Figure 3 showed TLC result for fresh sunflower oil of Rf value was 0.92.
and Rf value was gradually decreased under using repeated frying times.
Fourier Transform Infrared Spectroscopy (FTIR) Analysis
FT-IR spectroscopy is an excellent tool for analysis as the intensities of the bands in
the spectrum are propotional to concentration (Guillen and Cabo, 2000). The present study is
conserved with degradation of lipid during repeatedly cooked oil infrared region in mid IR
(400-4000CM-1) is the most commonly used region for analysis (Figure Number). Since the
molecule characteristic absorbance frequencies and primary molecules in the ranges, the
chemical change in the functional group of lipid was monitored using FTIR.
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The functional groups present in molecules tend to absorb IR radiation to the wave
number less of the other structure in the molecules.FT-IR spectra of sunflower, groundnut
and palm oil showed that there exists a notable difference in the band at room temperature, at
boiling point and between the same oil used for frying three times with a vegetables.
The oil composition affects the exact positions of the band and yields a shift when the
proportion of fatty acids changed.
Figure 4 FT-IR Spectrum of first time frying sunflower oil
3500 3000 2500 2000 1500 1000 500
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Figure 5 FT-IR spectrum 2nd frying of sunflower oil
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At diffrent temperatures and during frying three times with a homemade food , the
percentage transmittance of almost all the peaks increased indicating a decrease in bsorbance
which may be due to decomposition of hydroperoxides secondary oxidation initiation(Erum
Zahir and Anjum Yousuf 2014) The result of FTIR study indicated a pronounce difference
between control and repeatedly used frying sunflower oil samples. Figure 6 shows fresh
Sunflower oil the FTIR spectra exhibited a peak 3685CM-1 denote O-H stretching of alcohol
groups in lipids. Figure 4 shows FTIR spectra has total 16 frequency peak functional group
present in fresh sunflower oil. Sunflower oil was first time cooked frying oil sample revealed
highest peak 3555CM-1 indicated O-H stretching groups. First time cooked frying oil has 15
frequency and their functional groups present in oil sample. New functional groups were found
in cooked frying oil.FTIR spectra revealed highest peak value of 3553CM-1 but this do not useful
for edible oil content. This oil sample was second time cooked frying oil contain new functional
group found in this oil sample. The peak value of 1102CM-1 indicate the presence of C-N
Journal of Information and Computational Science
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stretching band of amine functional group. These amine group was present in edible oil gives
toxic into human health. The total 19 peaks value were present in second time cooked frying
oil.Sample 4 FTIR spectra revealed 16 peak values. The peak values of 1236CM-1 and 1103CM-1
were indicated the presence of C-N stretching group. Which is obtained in edible oil gives toxic
into human health. Hence these results indicated that we should avoided repeatedly used cooking
oil for deep fried foods.
Figure: 6 FT-IR Spectrum fresh sunflower oil
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3500 3000 2500 2000 1500 1000 500
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In this present study result indicates that should not used oil again and again for cooking.
Because the chemical changes in as edible oils were observed from evaluation of chemical
properties such as Peroxide value, Saponification value, Iodine value and Acid number. FTIR
analysis showed that highly significant difference between control and repeatedly using cooked
oils.
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Conclusion
Thus overall studies clearly indicate that edible oil becomes highly viscous and presence of
harmful products increases when oil is heated repeatedly. Deep frying is the most common and
one of the oldest methods of food preparation worldwide. To reduce the expenses, the oi tends to
be used repeatedly for frying. Repeated use of this oil has become a common practice due to low
level of awareness among the public about the bad effect of this practice. Now-a-days, the
consumption of deep fried food has gained popularity which may cause increased risk of obesity.
Reusing cooking oil without using antioxidant is extremely harmful to your health according to
the nutritionist. Reusing cooking oil increases the cholesterol, creates peroxides acid causes
cancer, attacks organ cells and can infect the white blood cells. Repeatedly frying oil now
becomes dangerous for human consumption. Therefore, oil should not be heated again and again
the formation of harmful products can be minimized by discarding it or using it with certain
antioxidants.
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