evaluation of chemical changes in different commercial oils ...

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: [email protected]

Journal of Information and Computational Science

Volume 10 Issue 1 - 2020

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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.



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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.



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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.



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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

Wavenumber cm-1

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Figure 5 FT-IR spectrum 2nd frying of sunflower oil

355

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3500 3000 2500 2000 1500 1000 500

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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



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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

793

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3500 3000 2500 2000 1500 1000 500

Wavenumber cm-1

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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