IJERD – International Journal of Environmental and Rural Development (2014) 5-2

Research article
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The Effect of Heating on Vitamin E Decomposition inEdible Palm Oil
NATTAWAN KUPPITHAYANANT*Rajamangala University of Technology Thanyaburi, Pathumthani, Thailand
Email: kuppithayanant@yahoo.com

PISIT HOSAP
Rajamangala University of Technology Thanyaburi, Pathumthani, Thailand

NUCHTIDA CHINNAWONG
Rajamangala University of Technology Thanyaburi, Pathumthani, Thailand
Received 11 March 2014

Accepted 28 August 2014(*Corresponding Author)

Abstract Currently, palm oil is popular in consumption, and vitamin E in palm oil has
been used to indicate the quality. In addition to complexity processing of crude palm oil toedible oil that loses vitamin E, the use of high-heat for cooking, can cause vitamin decay.
Therefore, this research aims to study the limit of how much heat affects on vitamin E
decomposition; and this result will bring useful information to apply in cooking. This
investigation was performed with oil having vitamin E concentration at 80 mg l-1 to beheated. Samples were collected when the oil was heated and started smoking and samples
were collected every 15 minutes. Then, the samples were analyzed for the vitamin E
through the extraction process of a solid phase extraction (SPE), which uses C18 as solidsorbent and dichloromethane as eluent Gas chromatography equipped with flame
ionization detector (GC- FID) was operated under the temperature programming mode forquantitative analysis. The results show that the percentage of vitamin E degradation would
continuously increase in temperatures ranging from 210 °C to 278 °C and this degradation
rate still constant after a half of hour expansion for oil heating at 278 °C. So, it’sconcluded that longer time used in the heating process could affect less to the vitamin E
decomposition than increasing the temperature.
Keywords edible palm oil, vitamin E decomposition, SPE, GC - FID

INTRODUCTION
Vitamin E under the term of α - tocopherol is a powerful biological antioxidant. The major
biological role of vitamin E is to protect unsaturated fatty acids contained in vegetable oils fromoxidation by free radicals (Gordon and Kourimska, 1995). It’s believed to reduce the risk ofcardiovascular diseases and of certain types of cancer. The main sources of vitamin E in the humandiet are vegetable fats and oils. Due to that palm oil contains more saturated fatty acids (up to 50%)and is rich in vitamin E, it can be resistant to the high heat and is resistant to oxidation (Burton andTraber,1990). So for this reason, palm oil is currently the most consumed edible oil in the world.
The refining process of edible palm oil industry affects the breakdown of vitamins, so industrial
palm oil has added vitamin E before bringing it to the market (Clegg, 1973). Although, vitamin E isrelatively resistant to heat and insoluble in water, the high heat cooking such as frying oil can causea loss of vitamin E. In addition the cooking time and cooking method affect loss vitamins E aswell.
Sample treatment for vitamin E analysis often includes saponification, of an isolated lipid
fraction. Saponification prior to the extraction is classically performed by heating with potassiumhydroxide in ethanol or methanol and analyzed directly. Solid phase extraction (SPE) is a wellestablished method for the concentration and extraction of matrices in various samples. In addition,Ⓒ ISERD

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the use of SPE has also proven to be an efficient technique for simplifying sample clean- up(Bonvehi, Coll and Rius, 2000).
The tocopherol content of oil and fat can be determined by a wide range of analyticaltechniques such as spectrophotometer, chromatographic techniques such as supercritical fluid
chromatography (Manninen, Laakso and Kallio,1995), gas chromatography (Lechner, Reiter andLorbeer,1999; Demirkaya and Kadioglu,2007), high performance liquid chromatography (Rupe´rezand et. al., 2001; Schwartza and et. al., 2008). Gas chromatography with flame ionization detection(GC-FID) has been used at a lesser extension to determine vitamin E compare with highperformance liquid chromatography. The GC analysis of tocopherols normally implies warm
saponification prior to the chromatographic injection (Rupe´rez and et. al., 2001).
This research aims to study the limit of how much heat affects vitamin E decomposition andthis result will bring useful information to apply in cooking.
OBJECTIVESThe objectives of this study are;
1. To determine Vitamin E from heated oil using SPE and GC-FID
2. To identify of how much temperature affects vitamin E decay
METHODOLOGY
Reagents and Standard Solutions
Vitamin E (DL- α – tocopherol), n - hexane, methanol and dichloromethane were purchased from
Merck (Darmstadt, Germany). Standard stock solution of vitamin E was prepared in hexane to aconcentration 500 mg l-1 and stored in the dark under refrigeration. Working standard solutions at30, 40, 50, 80, 100 and 120 mg l-1 concentrations were prepared freshly by diluting with hexane.
Commercially edible palm oil sample was bought from the local market.
Sample Preparations
Due to the complex composition of edible oil, it was necessary to eliminate large molecularcompounds via saponification method for investigation of the performance of analysis method. For
saponification, 21.25 g of edible palm oil was placed in an Erlenmeyer flask to which the mixtureof 15.5 g l-1 800 ml ascorbic acid solution and 10% w/v potassium hydroxide in 200 ml ethanol
were added. After heating the mixture solution to 70 °C in oven for 30 min, the saponification
solution was allowed to cool down and 25 g NaCl was added to accelerate phase separation. The
upper layer was extracted repeatedly with n–hexane and an aliquot of n–hexane was spiked of 70
mg l-1 vitamin E before analysis method that included of SPE followed by GC–FID.
For the study of heat affect to vitamin E decomposition, 0.3333 g. of vitamin E was directly
added to 500 ml of edible palm oil (approximately 80 mg l-1 concentration). The oil sample washeated until start to smoke and immediately collected 1.2 ml of oil and then diluted to 10 ml. withhexane. Thereafter the sampling was done in the same manner by continuing to keep every 15
minutes until the oil temperature remains constant and the sampling continued for another 3 times
then each sampling oil was analyzed method for vitamin E determination.
Instrumentation and Analytical Conditions
Chromatographic analysis was carried out on Varian CP 3800 gas chromatography systemequipped with a flame ionization detector. ZB - 5 capillary column (30 m x 0.25 mm I.D. x 0.25
μm. film thickness, USA) was used. H2 gas was used as carrier gas at a flow–rate of 4 ml min-1 andsplitless injection was used. The injector and detector temperatures were 255 °C and 300 °C. Theoven temperature set at 200 °C held for 1 min then increase to 300 °C at rate 25 °C min-1 and held
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at 300 °C for 5 min. Quantitative analysis of vitamin E in edible palm oil was performed using
standard addition technique, from the standard curve of peak area vs. concentration.
In all SPE experiments, C18 cartridges were conditioned with 6 ml of distilled water,methanol, isopropanol and dichloromethane, respectively. The amount of 1 ml of edible oil solution
with 70 mg l-1 of vitamin E concentration was twice loaded to SPE cartridge (1 ml per each) andsoaking for about 5 minutes and then letting it flow out under the atmospheric flow rate. Afterloading oil sample, the cartridge was dried under vacuum, to elute vitamin E from cartridge withthe same manner as in loading step except soaking time was performed at 30 min. Then thissolution was injected to GC – FID for analysis.
RESULTS AND DISCUSSION
Validation of the Analysis Method
For GC - FID analysis, the chromatogram show the retention time of vitamin E in standard solution
at 5.735 min. The linearity of the peak area response versus concentration was obtained in theconcentration range between 30 to 120 mg l-1 (r2 = 0.995). Precision was determined both withinday and between-day. Repeatability or within - day precision was tested by 7 times analysis of100mg l-1 standard vitamin E solution. The intermediate precision (between – day) was set 3 times
analysis of the same concentration as above. The repeatability express as relative standard deviation(% RSD) was 3.11% and the intermediate precision (% RSD) was 2.84%. The limit of detection(LOD) was determined from the intercept of the regression line of the calibration graph using a 30 to120 mg l-1 concentration range. The LOD was set equal to three times the standard deviation of thearea at the intercept and illustrated approximately 8.01 mg l-1.
For the evaluation of the extraction recovery, palm oil was spiked with 70 mg l-1 vitamin E. The
recovery was calculated by comparing the quantitative results obtained by SPE - GC analysis andactual spiked concentration. The percentage recovery was found between 80.1- 86.9% with relativedeviations 3.1 (n=5). The results of recovery and validation values are shown in Table 1.
Quantification of Vitamin E in edible palm oil was determined via standard addition method and thevitamin E content found in oil was 25.36 mg l-1.
Table 1 Linearity, precision (%RSD), LOD of GC – FID analysis and %recovery of theanalysis SPE – GC-FID analysis
Concentration
range ofLinearity(mg l-1)
30 - 120

GC – FID analysis% RSD% RSDWithin – day
Between – day(n=7)(n =3)
3.11
2.84

SPE – GC-FID analysis
LOD(mg l-1)% Recovery% RSD( n= 5)8.01

80.1 – 86.9

3.1

Heat Affecting Decomposition of Vitamin E in Edible Palm Oil
The results of vitamin E decomposition on heating oil was found that the first sampling of oilsample start at 210 ºC. Vitamin E was reduced approximately 6.38% compare with the amount ofvitamin E before heated. The heating oil sample still collected continuity every 15 minutes until
reach to constant temperature (278 ºC). At this temperature, the sample was further collected for 3times (15 minutes/each). The decay rate of vitamin E increased rapidly up to 60.70% at the highest
temperature (278 ºC) and the decay rate of vitamin E did not significantly increase after expansionof heated time (Table 2). Fig. 1 shows the vitamin E concentration at various heating temperatureand sampling time. This result illustrated that oil heated to 278 ºC is not sufficient to completely
decompose vitamin E. From the previous research, thermal decomposition of vitamin E in edible
oil was completely at about 773 K (500 ºC) (Arora, Bagoria, and Kumar, 2010). It can be noticed
that the heating temperature is a more significant factor than the heating time. Generally, the mostof food cooking needs high heat, which influences the breakdown of vitamin E during the cookingⒸ ISERD123

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process.
Table 2 Heating time, heating temperature and Vitamin E decay after heatedSampling numberand time(min)Temperature(°C)

1 (Spiked solution)
2 (0 min)3(15 min)
4 (30 min)
5 (45 min)
6 (60 min)
7 (75 min)

30
215
255
261
278
278
278

Vitamin E
concentration(mg l-1)
79.9
74.8
64.1
46.7
31.4
30.9
30.3

Concentration ofvitamin E decay(mg l-1)
05.1
15.8
33.2
48.5
4949.4% Vitamin E
decay (mg l-1)
06.4
19.8
41.6
60.7
61.3
61.8

90

(mg/l)
concentration(mgVitaminE El-1)
concentration
Vitaminbefore heated
beforeheated80

startsmoking
smoking
startoil, oil,00 min.min

30 °C

30℃
70215°C
215℃

min.
1515min
255 °C
255℃

6050

30 min.

30 min261 °C
261℃

4045min.

60min. 75min.

45 min60 min75 min30278 °C

278℃

278℃
278 °C

278℃
278°C

20Fig. 1 Vitamin E concentration at various heating temperature and sampling time
1

0.94
0.9

0.84
0.8

0.8/ Ao
AxAx/Ao

0.7

0.68

0.7
0.6

0.5

0.53

0.53

0.54
0.5

0.4

0.35

0.3

0.35

0.35

0.2
010

2030

4050

60

7080

Heating times
Heatingtimes(min.)(min)Fig. 2 Comparison of the ratio of the peak area of vitamin E in oil after heated (Ax) to a peakarea of vitamin E in oil before heated (Ao) of oils with and without vitamin E addedⒸ ISERD124

IJERD – International Journal of Environmental and Rural Development (2014) 5-2

This work was created in the trial to confirm that vitamin E that is already present in edible
palm oil has degraded as well by heating palm oil samples without added vitamin E. The results
were expressed by using the ratio of the peak area of vitamin E in oil after heated (Ax) to a peakarea of vitamin E in oil before heated (Ao) of both oils (with and without vitamin E added). Thoseof experiments were shown in Fig. 2 and it can be noticed that vitamin E decay rate of oil with andwithout vitamin E added were similar.
CONCLUSION
In conclusion, the analysis method to determine vitamin E in edible palm oil was completely
validated by using linearity, precision, limit of detection and accuracy in term of percentage ofrecovery. Vitamin E in edible palm oil can be decomposed during high heat cooking process andthe time used to heat oil was less affect to vitamin E decomposition than temperature increasing.
ACKNOWLEDGEMENTS
The authors acknowledge Faculty of Science and Technology, Rajamangala University ofTechnology, Thanyaburi (RMUTT) for financial support.
REFERENCES
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Lechner, M. Reiter, B. and Lorbeer, E. 1999. Determination of tocopherols and sterols in vegetable oils bysolid-phase extraction and subsequent capillary gas chromatographic analysis. J. Chromatogr. A., 857,231-238.
Demirkaya, F. and Kadioglu, Y. 2007. Simple GC-FID method development and validation for determinationof α-tocopherol (vitamin E) in human plasma. J. Biochem. Biophys. Methods, 70, 363-368.
Rupe´rez, F.J. Mart´ın, D. Herrera, E. and Barbas, C. 2001. Chromatographic analysis of a-tocopherol andrelated compoundsin various matrices. J. Chromatogr. A., 935, 45-69.
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