Radical Scavenging Activity of Tertiary Butyl Hydroquinone and Assessment of Stability of Palm Oil ( Elaeis guineensis ) by Ultrasonic Studies

The aim of the current investigation is to evaluate the efficiency of tertiary butyl hydroquinone (TBHQ) as an antioxidant in edible oil like palm oil (Elaeis guineensis) by physical, chemical and ultrasonic properties. The effects of the varying amounts of TBHQ on the oxidation stability of palm oil have been investigated. The antioxidant incorporated palm oil system and control oil were subjected to heating at 180 ± 5 °C continuously for a period of 4 h per day for 4 days consecutively. The parameters used to assess the thermal degradation and oxidation properties of the palm oil include ultrasonic velocity, viscosity and density. Adiabatic compressibility, intermolecular free length, relaxation time, and acoustic impedance have been calculated from experimental data. The effect of thermal ageing on the physical properties of the oil was confirmed by chemical analysis, which included free fatty acid, total polar compounds, and estimation of fatty acids profile by gas chromatography (GC). The chemical changes were studied by FT-IR bands. The results obtained from ultrasonic studies have shown improvement in oxidative stability and retardation in thermal degradation of the antioxidant-loaded oil in comparison with the base oil. Hence, the ultrasonic velocity and acoustical parameters used for assessment of stability of frying oil and palm oil with TBHQ can be recommended for repeated frying without adverse effects on the physical properties.


Introduction
Heat treatment is a widely used process in food processing industries.As heat-processed foods are much appreciated, analytical studies that can assess the changes caused by heating have been demanded from researchers [1][2][3][4] .Oils and fats, when heated, suffer thermal oxidation and produce compounds such as peroxides.The peroxides turn into aldehydes, ketones, epoxides, dimers and polymers, undermining the quality of food 5 , while the physical properties of the oils and fats are changed 6 .In order to minimize such effects, the food industry makes use of antioxidants 7 .The important antioxidants used in the food industries are butylated hydroxyanisole (BHA), butyl-1-4-hydroxytoluene (BHT), tert-butyl hydroquinone (TBHQ), and propylgallate (PG), of which TBHQ has been found to be the most effective antioxidant 8,9 .
According to USDA code of Federal Regulations, 'antioxidants' are substances used to preserve fats, oils, and foods by retarding deterioration, rancidity or discolouration due to oxidation.Edible oils with unsaturated fatty acids, especially polyunsaturated fatty acids, are more susceptible to oxidation 10,11 .The use of antioxidants is the most preferred way to inhibit lipid oxidation 12 as the addition of polyphenols to foods and biological systems scavenge free radicals [13][14][15] .
The activity of an antioxidant can be estimated by quantitative estimation of primary or secondary products of autoxidationof fats 16,17 , oils, and foods or by monitoring other variables.The primary products such as hydro peroxides formed during lipid oxidation are measured by iodometric titration, which is generally expressed as the peroxide value (PV) 18,19 .The secondary products of oxidation occur when the hydroperoxide decompose to form carbonyl and other compounds.Of the available methods for measuring hydroperoxides decomposition products, determination of aldehydic compounds (Anisdine value-AV, Thiobarbituric acid value-TBA) 20 , measurement of total carbonyls 21 or selected carbonyl compounds and assessment of off-flavours and off-odours due to the formation of volatile decomposition products of hydroperoxides by objective and subjective means are used extensively.Since these methods are time consuming and laborious, they cannot be employed for accepting or rejecting the products.Most sophisticated methods, such as nuclear magnetic resonance (NMR), near infra-red (NIR) spectroscopy, and mass spectra (MS) etc., 22,23,54 meet the requirements but are cost intensive.Therefore, a cost effective and simple analytical method needs to be developed to meet the above requirements.
Ultrasound represents an innovative, and emerging technology as a destructive or non-destructive one.It has a frequency range of 16-100 kHz (Power Ultrasonics) followed by a range from 100 kHz-2 MHz representing the sonochemistry range, and at the end the non-destructive range from 2 MHz up to 10 MHz [25][26][27] .Ultrasonic methods are simple, instantaneous, and cost-effective for the study of the physical characteristics of various oil products for quality control purposes 28 .Although limited information is available on the determination of physical properties of triglycerides by using the ultrasonic interferometry technique 29 , there is scarcity on its application in studying the molecular interaction between lipid and antioxidants.
A few studies have revealed that the measurement of viscosity and density can be used to determine the oxidative stability [30][31][32] , while ultrasonic velocity is used to understand the molecular interactions 29,33,34 in the oil.However, the effect of a synthetic antioxidant on the oils has not been fully elucidated by ultrasonic velocity.
Palm oil (PO) with its inherent frying properties is used due to its techno-economic advantages over other oils and fats.Past studies have demonstrated the frying performance of palm olein during continuous frying of snack foods 34 .Palm oil contains saturated fatty acids like palmitic acid (44.3 %), oleic acid (38.4 %) and linoleic acid (10.8 %), vitamin E especially tocotrienols, vitamin K and magnesium.The antioxidant activity of palm oil is due to the presence of carotenoids and vitamin E. Beta carotene is the reason for the yellow colour of the PO, it may also be an important factor for the free radical scavenging activity.However, palm oil is not very stable at high temperatures and deteriorates on repeated heating and/or frying.
The objectives of this research were: (i) to investigate the TBHQ activity in palm oil using ultrasonic velocity, density, and viscosity; (ii) to study the secondary parameters such as adiabatic com-pressibility, intermolecular free length, relaxation time, acoustic impedance, and (iii) fatty acid profile by gas chromatography (GC), total polar compounds (TPC), free fatty acid (FFA), and spectral changes in FT-IR to correlate the chemical changes in PO and antioxidant activity.

Materials
Fresh palm oil (PO) was obtained from Pentagon Overseas India Limited, India.TBHQ was purchased from Sigma Aldrich, and AR grade chemicals were used for the chemical analysis.Samples of palm oil (control) and palm oil with 50, 100, 150 and 200 ppm of TBHQ were heated in an oil bath at a temperature of 180 °C continuously for 4 h per day for 4 days.As per ISO 9001:2008 norms (Indian Standard Quality Management System requirements), 150 ppm of TBHQ is allowed in vegetable oils; however, the general standard for food additives allows 200 ppm (Codex 1995)  50 .Hence, a maximum of 200 ppm TBHQ has been used in this investigation.All measurements of heat-treated oils were carried out in triplicate and average values are reported.

Techniques
The density (ρ) of the pure oil and its mixtures was measured using a 10 mL specific gravity bottle, and distilled water was used as reference.The viscosity (η) of the oil and oil-antioxidant mixtures were measured using an Ostwald's viscometer immersed in a temperature controlled water bath (Advance Technocracy Inc.; Ambala; India).
The ultrasonic velocity (U) of PO with and without TBHQ were measured using an ultrasonic interferometer (Mittal Enterprises; New Delhi, India), at 2 MHz frequency with a tolerance of ± 0.005 %.The accuracy of the instrument is 0.1 m s -1 .
The adiabatic compressibility (β) is defined as the decrease of volume per increase of pressure when no heat flows in or out.Such a change is related to the compressibility of the medium by following the thermodynamic relation; where, V is the volume, δ v is the relative change in volume, and δ p is the relative change in pressure.It can also be calculated from the ultrasonic velocity (U) and the density (ρ) of the oil using Newton Laplace 35 equation as follows; The adiabatic compressibility of liquid can be expressed in terms of intermolecular free length (L f ), which is the distance between the surfaces of the neighbouring molecules and is given by the following equation; where, K T is the temperature-dependent constant, i.e. 201.1209 ⋅ 10 -8 at 303 K.The relaxation time is the time taken for the excitation energy to appear as transitional energy, and it depends on the temperature and impurities.The dispersion of the ultrasonic velocity in a mixture reveals information about the characteristic time of the relaxation process that causes dispersion.The relaxation time (τ) can be calculated using the following equation; 29 4 3 The specific acoustic impedance (Z) is as follows: 35 Z = U ρ ( where, U and ρ are the velocity and density of the oil, respectively.

Fatty acid by gas chromatography
Fatty acid methyl esters (FAME) of the oils were prepared by transesterification, according to AOCS method No: Ce 1-62, 1998 37 .FAMEs were analyzed by gas chromatography (GC) (Fisons 8000, Co., Italy), equipped with a hydrogen flame ionization detector (FID) and a fused silica capillary column (100 m × 0.25 mm i.d.), coated with 0.20 μm SP2560 (Supelco Inc., Bellefonte, PA) as the stationary phase.The oven temperature was programmed from 140 to 240 °C at 4 min -1 with an initial hold at 140 °C for 5 min.The injector and FID were at 260 °C.A reference standard FAME mix (Supelco Inc.) was analyzed under the same operating conditions to determine the peak identity.The FAMEs were expressed as relative area percentage.
The free fatty acid (FFA) content as the percentage of oleic acid was determined using AFNOR NF T 60-204 method.
The AOCS method Cd 20-91 was used to determine total polar compounds (TPC) of oil.A chromatogram column (21 mm i.d. and 450 mm long) was filled with about 30 mL of a mixture of light petroleum and diethyl ether (87:13, v/v).A wad of glass wool was introduced at the lower end of the column with the aid of a glass rod.Slurry of 24 g of silica gel in about 80 mL of the solvent mixture was poured into the column.The elution solvent was drained through the column until its level was 10 cm above the silica gel level.About 4 g of sea sand was added and the supernatant was drained down to the sand layer.In order to estimate TPC, 2.5 g of oil was dissolved in 20 mL of solvent mixture containing light petroleum and diethyl ether (87:13 v/v) at room temperature.The volume was then made up to 50 mL and the resulting solution was introduced into the column and drained off to the level of the sand layer.The non-polar compounds were eluted with 150 mL of solvent mixture at a flow rate of 2.5 mL min -1 .TPC was calculated using the following equation; where, m 1 is mass (g) of the non-polar fraction, and m is mass (g) of the sample containing 20 mL of solution added to the column.

Results and discussion
In this study, the effects of different heating times and different amounts of TBHQ addition on the thermal oxidative stability of palm oil has been investigated using parameters such as viscosity 27,33 , density, and ultrasonic velocity 34,35 .The study of thermal degradation and stability of the palm oil with antioxidant was carried out by heating the oil at 180 ± 5 °C for the desired time.The viscosity, density, and ultrasonic velocity of PO and PO with different concentrations of TBHQ were measured at 30 °C.
The effects of different heating time and TBHQ content on density (ρ) of PO are shown in Fig. 1.The density of heated palm oil gradually and substantially increased with heating time.Incorporation shows that the heat-treated control oil exhibits a drastic increase in viscosity of 1.6523 ⋅ 10 -1 N s m -2 , whereas the oil with 200 ppm of TBHQ had the lowest viscosity of 0.84419 ⋅ 10 -1 N s m -2 for 16 h heating time.The obtained results were in good agreement with the already publishresults 28,[38][39][40] .The viscosity of oil increases with duration of frying due to oxidation, isomerization, and polymerization reactions.An oxidation reaction leads to the formation of carbonyl or hydroxyl groups resulting in flux among the molecules that in turn increases the viscosity 33 .
The ultrasonic velocity and attenuation depends on the physico-chemical properties of the oil 41 .A majority of the studies have used ultrasonic evaluation of food, as it is more reliable than attenuation and related to the physical and chemical properties of the medium 42 .The variation in the ultrasonic velocity with heating time is indicated in Fig. 3.After each heating period the ultrasonic velocity increases, and thus it is possible to distinguish the two oils 29 .The changes in velocity of heat-treated oils are due to changes in the chemical composition of the oils.It was observed that the ultrasonic velocity increased linearly with heating time similar to the density and viscosity variations.The ultrasonic velocity increased significantly in the control oil from 1452 m s -1 to 1490 m s -1 after 16 h heat treatment.The smallest increase (1464 m s -1 ) in ultrasonic velocity was recorded for palm oil with 200 ppm TBHQ.
Figs. 4 to 7 illustrate the interaction between the ultrasonic waves and the composition of oil molecules.The adiabatic compressibility and free length are the deciding factors of the ultrasonic velocity in liquid systems 29 .The increase in the ultrasonic velocity was due to the decrease in the free length and adiabatic compressibility.The adiabatic compressibility and free length were found to differ slightly for oil with 200 ppm of TBHQ as compared to the changes in the base oil.The decrease in the values of the free length indicates that the triglyceride molecule with unsaturated bonds is likely to collapse as a result of the oxidation process 32 .The structures of triglycerides are kept intact due to the presence of TBHQ 41 in oil.Hence, the values of free length, which indicates the intermolecular distance, did no reduce as a result of using TBHQ.
The changes in the relaxation time of oil against heating time are plotted in Fig. 6.It was found that relaxation time increased with the heating time.The base oil showed greater enhancement in relaxation time, and its lowest increment was found in oil with 200 ppm of TBHQ.The dispersion of ultrasonic velocity in the system should contain information about the characteristic time, τ of the relaxation process that causes dispersion, where, τ is in the order of 1 ⋅ 10 -11 s due to the structural relaxation process 44 and in such a situation, the molecules rearrange due to a co-operative process 45 .The acoustic impedance is calculated using ultrasonic velocity and density, and was plotted as a function of heating time (Fig. 7).It was found that the acoustic impedance was low in the oil with TBHQ and without heating.With increased heating time, the acoustic impedance increased in the base oil, but to a very little extent in the oil with 200 ppm of TBHQ.The excess parameters play a major role in understanding the nature of intermolecular interactions in liquid mixtures 46 .The intermolecular free length and acoustical impedance depend upon the intermolecular attractive and repulsive forces.Excess acoustical impedance may be due to the pyrolysis effect allowing the fitting of molecules of different sizes after collapsing the triglyceride structure.
The measured acoustic parameters, such as β, τ, L f and Z, were correspondingly found to change to a large extent in the control PO.The addition of the antioxidant, TBHQ, allowed no breaking up of the molecular clustering in the oil.The interaction between the molecules of the oil occurred to a lesser extent, and hence, very small structural changes occurred during heating in the presence of an antioxidant.In the control oil, as the antioxidant activity is much less, a break up occurred in the molecular clustering, releasing several dipoles for the interaction.In view of the greater interactions, larger changes have occurred for heat-treated oils in the adiabatic compressibility, intermolecular free length, relaxation time, and acoustical impedance.It was found that the stability of PO with antioxidant TBHQ was better even at high temperatures and after prolonged heating 31,32 .
Gas chromatography (GC) is a useful analytical technique for studying the effect of different processing conditions on the fatty acid composition of oils 47 .Tables 1 and 2 present the results of the fatty The PO with 200 ppm TBHQ showed slight changes in the FA composition in heated oils, which reflected that antioxidant addition in unsaturated oils retards the degradation of oils.A reduction in the amount of linoleic acid was observed with the increase in concentration of oleic acid 18 .
The FA composition of oil has significant effect on its frying performance as well as on its physi-co-chemical behaviours.The FA profile of the frying oils changed as a result of cyclization, polymerization, and hydrolytic, oxidative and other chemical reactions promoted by frying conditions 48 .The linoleic acid level in deep-frying oils appears to be an obviously negative factor in oil stability.In this study, changes in the FA profile of oils during frying are basically among the unsaturated fatty acids, whereas the saturated fatty acids are slightly increased.

Fatty acid
Heating time (h) The frying stability of PO can be improved by incorporation of TBHQ, in order to reduce the change in linoleic and oleic acid, and consequently to improve their oxidative and heat stabilities.The data indicates that the amount of unsaturated fatty acid decreased gradually during repeated deep fat frying cycles.This may be due to oxidative and thermal degradation reactions during repeated deep fat frying cycles of the unsaturated fatty acid constituents of triacylglycerols 44 .Better oxidation stabilities were found in the formulated oils during repeated frying as compared to the base oil.Formation of free fatty acids (FFA) for heat-treated oil is considered to be a measure of rancidity of oils.The percentage of FFA formed for repeatedly heat-treated oil is presented in Table 3.Initially, the base oil and the TBHQ-loaded oils had a similar FFA content; as the heating time continued the palm oil showed a higher FFA value than the TBHQ-loaded oils.FFA is formed due to hydrolysis of triglycerides and may be promoted by the reaction of oil with moisture 49 .Addition of antioxidant caused a significant reduction in FFA values of PO.FFA content is the frequently used data to probe the shelf life of frying oil, but it is not recommended to be the only indicator.
Generally, degradation of oil during frying is accompanied increased polar compounds in the oils 50 .Many researchers have reported that total polar compounds (TPC) are the most reliable indicator of oil degradation 29,51 .Polar compounds include all oxidized triglycerides, dimerized triglycerides, FFAs, monoglycerides, diglycerides, sterols, antioxidants, antifoamers, hydrogenation catalyst residues and soaps 7 .Table 3 shows the percentage of TPC formed during heating in PO and PO with 200 ppm TBHQ.Initially, the TPC contents of the base oil and the formulated oil were similar.The increase in the rate of TPC formation with heating time in the base oil was different from the formulated oil with TBHQ.After 16 h of heating, the final TPC values were 22.3 % in the base oil and 11.5 % in the PO+ 200 ppm TBHQ.These parameters are indicators of the state of oil deterioration.These results clearly indicate that the PO with 200 ppm TBHQ was more stable chemically than PO.Polar compounds are the sum of non-triglycerides of oil including fatty acids, sterols, tocopherols, mono-and di-triglycerides, alcohols, aldehydes, ketones, and other soluble compounds in oil that are more polar than triglycerides 52 .Polar compounds accumulate on the surface of the frying pan and foods during frying.Most of the poisonous materials are considered to exist in the polar compounds of oil 53 formed during oxidation.If the TPC exceeds 25 %, according to FDA norms, the oil should be disposed 54 .It is observed that after 16 h of heating, polar compounds in the PO reached 22.3 %, and this may exceed 25 % on further heating.On the other hand, PO with 200 ppm of TBHQ reached 11.5 %, may not have polar compounds exceeding 25 % on further heating, and hence can be used.

Correlation of ultrasonic velocity with total polar compounds and free fatty acids
As long as the ultrasonic velocity is related to the physical properties of the medium like viscosity and density, velocity should also be related to these chemical indicators.The relationship between the ultrasonic velocity and both TPC and FFA for heated PO and PO with 200 ppm TBHQ at 30 °C are shown in Figs. 8 and 9, respectively.The changes in polar compounds with the change in ultrasonic velocity relationships are found to be linear with the regression value, R 2 = 0.982 in the case of base oil, and R 2 = 0.996 for TBHQ-treated oil 29 .The changes in FFA with change in ultrasonic velocity relationships are also found to be more linear with regression value, R 2 = 0.991 in the case of base oil, and R 2 = 0.983 for TBHQ-treated oil.These findings are in accordance with data found elsewhere 29,42 .These chemical parameters, widely considered as oil quality indicators and polynomial fits were found when relating the velocity.Therefore, measurement of ultrasonic velocity permits an estimation of the percentages of polar compounds and FFA independently in the oil.

FT-IR studies
The characteristics of FTIR for fresh PO, heated PO with and without antioxidant are shown in Fig. 10.The band at 3010 cm −1 is attributed to C-H stretching vibration of the cis-double bond 55 .Strong band absorptions were observed in the region 3000-2800 cm −1 corresponding to C-H stretching vibrations.The stretching vibrations of methylene (-CH 2 -) and methyl (-CH 3 ) groups can be seen at 2923 and 2854 cm −1 , respectively.The spectral region between 3050 and 2740 cm −1 undergoes several changes during the thermal oxidation process.
The changes in the FTIR spectra were observed for 16 hat 180 °C heated PO.The band at 2854 cm −1 and the shoulder at 2960 cm −1 increases their intensity and width for 16 h heated PO at 180 °C.Significant changes are noticed in heated base oil as compared to the heated PO with TBHQ.Methylene and methyl groups are also observed at 1463 cm −1 and 1376 cm −1 due to their bending vibrations.
Two absorption peaks observed at 1748 and 1160 cm −1 are due to the stretching vibrations of the aldehyde group (C=O) and ester group (C-O) respectively 56 .In the region of the former peak, infrared energy is absorbed due to the carbon-oxygen bonds in the oil, and it is often used for determining the level of oxidation.
The peak area around 1748 cm −1 is due to C=O bond stretching vibration.It is also interesting to follow the spectral changes in the C=O region (∼1748 cm −1 ).Here, the study shows changes in peak are at 1748 cm −1 for the heated samples.This observation is due to production of saturated aldehyde functional groups or other secondary oxidation products that cause an absorbance at 1728 cm −1 , which overlaps with the stretching vibration at 1746 cm −1 of the ester carbonyl functional group of the triglycerides.When new carbonyls are formed from initial aldehyde and ketone compounds, the maximum absorbance is in the region between 1720 and 1760 cm −1 resulting in a broadening of the 1748 cm −1 band.The total amount of carbonyls formed can be measured by the intensity and area of the 1748 cm −1 band.Also, it observed that height of the peaks in the heated PO is four times that of fresh PO at the regions 1463, 1376 and 1160 cm −1 and it is two times in the case of heated PO with TBHQ.The increases in the intensity of peaks indicate the changes in the chemical composition, and in turn, it is a sign of deterioration 47 .

Conclusion
In the current study, a method has been developed to make use of ultrasonic velocity to determine the thermal stability of palm oil.Incorporation of varying amounts of TBHQ (50, 100, 150 and 200 ppm) into PO provides improvements in the antioxidative potency.The addition of antioxidant, TBHQ at the level of 200 ppm, resulted in the retardation of oxidative deterioration of PO.Also in the present  and methyl (-CH 3 ) groups can be seen at 2923 and 2854 cm −1 , respectively.The spectral region between 3050 and 2740 cm −1 undergoes several changes during the thermal oxidation process.
The changes in the FTIR spectra were observed for 16 hat 180 0 C heated PO.The band at 2854 cm −1 and the shoulder at 2960 cm −1 increases their intensity and width for 16 h heated PO at 180 0 C. Significant changes are noticed in heated base oil as compared to the heated PO with TBHQ.Methylene and methyl groups are also observed at 1463 cm −1 and 1376 cm −1 due to their bending vibrations.
Two absorption peaks observed at 1748and 1160cm −1 are due to the stretching vibrations of the aldehyde group (C=O) and ester group (C-O) respectively 56 .In the region of the former peak, infrared energy is absorbed due to the carbon-oxygen bonds in the oil, and it is often used for determining the level of oxidation.
The peak area around 1748 cm −1 is due to C=O bond stretching vibration.It is also interesting to follow the spectral changes in the C=O region (∼1748 cm −1 ).Here, the study

Fig. 1 -
Fig.1 -Variation of density as a function of heating time for control palm oil and i composition with different tertiary butyl hydroquinone content F i g . 1 -Variation of density as a function of heating time for control palm oil and its composition with different tertiary butyl hydroquinone content

F i g . 2 - 29 Fig. 1 -Fig. 2 - 29 Fig. 1 -Fig. 2 -
Fig.1 -Variation of density as a function of heating time for control palm oil and its composition with different tertiary butyl hydroquinone content

F i g . 4 -
Variation of adiabatic compressibility of the control and palm oil with different concentrations of tertiary butyl hydroquinone with heating timeF i g .5 -Effect of heating time on intermolecular free length of the control and palm oil with different concentrations of tertiary butyl hydroquinone F i g .6 -Variation of relaxation time of the control and palm oil with different concentrations of tertiary butyl hydroquinone as a function of heating time F i g .7 -Variation of acoustic impedance of the control and palm oil with different concentrations of tertiary butyl hydroquinone as a function of heating time acid (FA) profiles of PO and formulated PO, respectively with heating time.The incorporation of TBHQ enhanced the oxidative stability of the heated oil samples.The estimated concentration of the unsaturated fatty acids by means of relative GC peak areas showed that palm oil treated with 200 ppm TBHQ had significantly lower values in comparison with the base oil.

1 CFig. 11 -
Fig.11 -FTIR spectra of fresh palm oil and heated palm oil with and without TBHQ; (a) 1500 cm −1 to 1100 cm −1 , (b) 1780 to 1680 cm −1 and (c) 3050 to 2750 cm −1The characteristics of FTIR for fresh PO, heated PO with and without antioxidant are shown in Fig.10.The band at 3010 cm −1 is attributed to C-H stretching vibration of the cisdouble bond55 .Strong band absorptions were observed in the region 3000-2800 cm −1 corresponding to C-H stretching vibrations.The stretching vibrations of methylene (-CH 2 -)

Fig. 11 -Fig. 11 -
Fig.11 -FTIR spectra of fresh palm oil and heated palm oil with and witho cm −1 to 1100 cm −1 , (b) 1780 to 1680 cm −1 and (c) 3050 to 2750 cm −1 The characteristics of FTIR for fresh PO, heated PO with and with shown in Fig.10.The band at 3010 cm −1 is attributed to C-H stretching v double bond 55 .Strong band absorptions were observed in the region corresponding to C-H stretching vibrations.The stretching vibrations of m and methyl (-CH 3 ) groups can be seen at 2923 and 2854 cm −1 , respect region between 3050 and 2740 cm −1 undergoes several changes during the process.The changes in the FTIR spectra were observed for 16 hat 180 0 band at 2854 cm −1 and the shoulder at 2960 cm −1 increases their intensity heated PO at 180 0 C. Significant changes are noticed in heated base oil a heated PO with TBHQ.Methylene and methyl groups are also observed 1376 cm −1 due to their bending vibrations.Two absorption peaks observed at 1748and 1160cm −1 are due vibrations of the aldehyde group (C=O) and ester group (C-O) respectively the former peak, infrared energy is absorbed due to the carbon-oxygen bon is often used for determining the level of oxidation.The peak area around 1748 cm −1 is due to C=O bond stretching v interesting to follow the spectral changes in the C=O region (∼1748 cm −