http://www.revistadechimie.ro REV.CHIM.(Bucharest)♦ 67♦ No. 4 ♦ 2016724

Sunflower Oil Behaviour During Storage Time

CLAUDIA COBZARU1, NICOLAE APOSTOLESCU1, GABRIELA ANTOANETA APOSTOLESCU1, ADRIANA MARINOIU2,MIHAELA SILION3, CORINA CERNATESCU1*1 Gheorghe Asachi Technical University of Iasi, Faculty of Chemical Engineering and Environmental Protection, 73 D. MangeronBlvd., 700050, Iasi, Romania2 National RD Institute for Cryogenics and Isotopic Technologies- ICIT, 4 Uzinei Str., 240401, Rm Valcea, Romania3 Petru Poni Institute of Macromolecular Chemistry, 41 A Gr. Ghica Voda, 700487, Iasi, Romania

In this paper, the influence of storage time on the composition of sunflower oil has been investigated.Parameters like free fatty acids (FFA), anisidine value (AV), iodine value (IV), saponification number (SN)were studied and identification of the molecular structure through FT-IR and HPLC-UV methods have beenmade. During storage (48 months) an increasing in the values of parameters FFA and AV took place, thatmeasures the oxidative degradation of the oil. The oxidative stability of the sunflower oil samples stored atroom temperature was high. However, the acidity of the sunflower oil increases very little in during storageperiod.

Keywords: sunflower oil, storage time effect, oil composition

Sunflower oil is a high quality fatty oil, obtained fromseeds of Helianthus annuus L. by mechanical expressionor by extraction, both followed by purification. It is the mostused product for cooking, frying and in the manufacture ofmargarine and shortening. Also, the sunflower oil is usedfor obtaining biodiesel [1-3]. According to the literature,the chemical composition of the sunflower oil (% w/w) is:myristic 0.1 max., palmitic 5-8, palmitoleic max 0.5, stearic2.5-7.0, oleic 13-40, linoleic 40-74 and linolenic max 0.3acids [4]. The variation of the unsaturated fatty acidscontent is strongly influenced by both genetics and climate.Also, sunflower oil contains lecithin, tocopherols,carotenoids and waxes. It is light in taste and appearanceand has a high content of vitamin E [5-7].

Because sunflower oil contains less stable poly-unsaturated and monounsaturated fatty acids, it can beparticularly susceptible to degradation by heat, air, and light.Keeping sunflower oil at low temperatures duringmanufacture and storage can help minimize rancidity andnutrient loss, as can the storage in bottles that are made ofeither darkly-colored glass or plastic that has been treatedwith an ultraviolet light protection agent [8]. On the otherhand, at high temperature and in the presence of air, manychemical reactions can be observed in oil such as:hydrolysis, polymerization, oxidation and isomerization [9].

The storage techniques for vegetable oils are veryimportant, not only to preserve the delicate taste of the oil,but also to ensure that it does not spoil, which will have anegative effect on its nutritional profile [10].

These reasons explain the opportunity of our study wherewe investigate the influence of the storage time on thecomposition of sunflower oil. Thus, we monitored thesunflower oil during 48 months to reveal the changes intheir composition in terms of acidity (determination of freefatty acids), lipid oxidation (determination of anisidinevalue), oxidative rancidity (determination of iodine valueand saponification number), identification of the molecularstructure (using FT-IR and HPLC-UV methods for analysisof the triacyl-glycerols).

* email: ccernatescu@yahoo.com

Experimental partMaterial and method

For this study refined sunflower oil commerciallyavailable has been used. The samples of the sunflower oilwere stored in PET bottles at room temperature during theanalysis period. Samples for the oil were took and analyzedat five time intervals namely: freshly bought, 12 months,24 months, 36 months and 48 months. The samples werecalled as SFO, SFO 12; SFO 24; SFO 36 and SFO 48.

Chemical reagents used for determination of the freefatty acids (FFA), the anisidine value (AV), the iodine value(IV) and saponification number (SN) for the all sampleswere purchased from Merck.

The free fatty acid (FFA) value in terms of % oleic acid,the saponification number (SN) and the iodine value weredetermined through methods of analysis detailed inliterature [11]. Also, anisidine value was determined bythe standard method [12] using a Shimadzu UV-VisibleSpectrophotometer. The analyses were conducted intriplicate for each sunflower oil sample and the arithmeticmedia have been noted in the paper.

FT-IR AnalysisAll infrared spectra (4000-650 cm-1) were acquired with

a Perkin Elmer Spectrum 100 FT-IR spectrometer. Thisinstrument was equipped with a horizontal attenuated totalreflectance (HATR) sampling accessory and ZnSe crystal.HATR accessory was used to collect the spectral data ofoil. The resolution was set at 2 cm-1 and the number ofscans collected for each spectrum was 128. ZnSe crystalwas cleaned with ethanol in between sample runs.Measurements were conducted in duplicate or triplicatefor each sunflower oil sample and the arithmetic mediahave been noted in the paper.

HPLC AnalysisDerivatization of sunflower oil sample

The IUPAC standard method for preparation of themethyl esters of fatty acids at room temperature [12] was

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applied with slight modifications namely: a mixtureconsisting of 1 mL solution of the sample, 1 mL ethanoland 3 mL acetone was added into a glass. Then a 1 mLvolume of a 0.5 n KOH solution in methanol was addedand vigorous shaking was applied for 20 s. After shaking,the mixture was neutralized with 1 mL of a 0.5 n HClsolution for 10 s. A volume of 50 µL of sample was injectedin the HPLC chromatograph.

HPLC MeasurementsThe derivatized oil samples were analyzed in a HPLC

chromatograph. The HPLC analyses were carried out usingan Agilent Technologies 1200 Series system, equipped witha binary pump, heated column compartment, automaticinjection system (autosampler) and diode array detector(UV-Vis DAD). The optimal conditions for separations wereachieved using a Zorbax SB-C18 reverse phase column(4.6 mm x 250 mm, 5 µm particle size) with a columntemperature kept at 25oC, using a 50 µL injection volum,solvent flow 0.6 mL/min and isocratic elution with mobilephase acetonitrile-tetrahydrofuran 3-1 (v/v). The solventswere filtered and degassed before use. The separationprocess was monitored by UV-VIS DAD detector at 220nm. Measurements were conducted in duplicate for eachsunflower oil sample.

Results and discussionsFree fatty acid value (FFA)

Free fatty acid value was used to assess the degradationof triglycerides and free acid content of the sunflower oil inall the samples. The changes in the free fatty acid value(FFA) for all samples, expressed in term of % oleic acid arepresented in figure 1.

samples by the changes in free fatty acid value weresignificantly studied in literature [16, 17].

The saponification number (SN)The saponification value is an indication of the molecular

weights of triglycerides in oil. According to the literature,higher saponification value indicates higher proportion oflower fatty acids because saponification value is inverselyproportional with the average molecular weight or chainlength of the fatty acids. Thus, shorter the average chainlength the higher is the saponification number [18]. Thesaponification number (SN) for the all samples arepresented in figure 2.

From figure 2 it can be observed that the saponificationnumber of the fresh sample (SFO) falls into the permittedstandard level (184-198 mg KOH/g oil) [19] which suggestthat it contain a high proportion of lower fatty acids. On theother hand the SFO 12, SFO 24, SFO 36 and SFO 48 samplesare lower (70.03-103.792 mg KOH/g) than the permittedstandard level which suggest that they have high contentof long chain fatty acids hence are unsuitable for soapmaking and also unsuitable for human nutrition [20].

As can be seen in figure 1, the initial FFA value of thefresh sunflower oil sample (SFO) is about 0.17%. Accordingto the literature, the free fatty acid value (FFA) expressedin term of % oleic acid for the refined sunflower oil isbetween 0.1% (for quality I) and 0.4% (for quality II) [11]which denotes that a sunflower oil of first quality has beenused in this study. The amount of free fatty acids in oil wasfound to increase with time of storage. Thus, after 12 monththe FFA value is about 0.2 % and then after 48 months ofstorage it increases slightly reaching to 0.5%. The increaseof the free fatty acids content even after 12 months storageleads to fact that the quality of the sunflower oil decreases.The increase in content of free fatty acids should be causedby different species of microorganisms that can get intothe oil in various stages of processing and transport withinthe plant [13], or could be attributed to oxidation andhydrolysis processes which produce FFAs [14, 15]. Thephenomenon of lipid oxidation in analyzed sunflower oil

Fig. 1. The FFA (% oleic acid) values of sunflower oil samplesduring storage period

Fig. 2. The saponification number for sunflower oil samples duringstorage period

It can be mentioned that the storage of sunflower oil inPET packaging does not affect the deterioration of oilcaused by triglycerides hydrolysis. The fluctuations of thesaponification value for the analyzed samples can beattributed to the light impact showing that the transparentpackaging does not prevent progress of the light throughthe walls of the packaging and that edible oil packing andstoring in PET bottles is not the best solution [21].

The iodine value (IV)According to the literature, the iodine value is an

indicator of the lipid oxidation and the degree ofunsaturation, a great iodine value indicating oils prone tooxidation. Furthermore, the unsaturated character affectsthe stability of oils and leads to the appearance ofdegradation effects during storage [22, 23]. The iodine value(IV) for all samples are presented in figure 3.

As can be seen in figure 3, the iodine value of the SFOand SFO 12 sunflower oil samples is very high, but still inthe permitted standard level (the standard iodine value ofthe sunflower oil is between 119 and 135 [19]. On theother hand the SFO 24, SFO 36, and SFO 48 samplesdecrease from 120 to 90 at the end of the 48 months. Thisfact suggests decreases in the degree of unsaturation ofthe oil caused by the extent of oxidation [24], but may bethe result of light impact on creating radicals on unsaturatedhydrocarbon chain, which could connect and obtaincomplex compounds such as dienes and polymers [21,25]. Similar results were published in literature [26] forauto- and photo- oxidized sunflower oil samples were the

http://www.revistadechimie.ro REV.CHIM.(Bucharest)♦ 67♦ No. 4 ♦ 2016726

iodine values found to decrease from 139.0 to 127.5 andfrom 139.0 to 123.3.

The anisidine value (AV)The susceptibility of sunflower oil to oxidation was

measured by anisidine value (AV). The anisidine value (AV)for all analyzed samples are presented in figure 4.

From figure 4 we can see that the susceptibility tooxidation is affected by the storage conditions. Thus, duringthe storage period, the anisidine value of the analyzedsunflower oil increases continuously. This fact can be aresult of the decomposition of hydroperoxides or of a non-volatile portion of the fatty acid occurs that remains a partof the oil. This non-volatile reaction product causes anincrease in anisidine value. Also, the anisidine valuesindicate the level of aldehyde, the effect of auto- and photo-oxidation reactions during oil storage. These results are inagreement with the literature data that confirm thedecreasing in oil quality during storage [26] and also areaccording to the results obtained for iodine value.

FT-IR analysisA study of literature suggests that IR spectroscopy can

be considered as a vital technique for identification,analysis, determination of degree of saturation of fattyacids and detection of adulteration of oils of plant origin[27].

In order to determine the degree of unsaturation theFT-IR analysis for all sunflower oil samples have beenrealized (fig. 5).

In all the spectra presented in figure 1, it can be seen thefollowing bands which are same or close to those fromliterature [28]: 3008 cm-1 attributed to the trans =C–Hstretch (in all spectra), 2953 cm-1 corresponding to –CH3asymmetrical stretch (in all spectra), 2922 and 2852 cm-1

due to asymmetrical and symmetrical stretching vibrationsof –CH2 (in all spectra), 1743 cm-1 for –C=O stretch (in allspectra), 1654 cm-1 corresponding to cis –C=C stretch(SFO 48 sample is empty), 1463 cm-1 corresponding to –CH2 bending (in all spectra), 1417 cm-1 attributed to cis=C–H bending (in all spectra), 1377 cm-1 attributed to –CH3 bending (in all spectra), 1238 cm-1 corresponding to –C–O stretch (in all spectra), 1159 cm-1 attributed to –C–Ostretch which are correlated to stretching vibration of C-Oester group (in all spectra), 1120 and 1033 cm-1

corresponding to –C–O stretch (in all spectra), 1097 cm-1

corresponding to –C–O stretch (in all spectra), 966 cm-1

due to trans –CH=CH– bending out of plane (in all spectra)and 723 cm-1 due to cis –CH=CH– bending out of plane (inall spectra).

These bands are more significant in fresh oil sample(SFO). For the specified wavelengths the peak heightincreases in case of the fresh oil sample and decrease incase of the SFO 12, 24, 36 and 48 samples. The spectralband near 1650, 966 and 723 cm-1 corresponds to thedouble C=C link and specifically to fresh sample (SFO)may be related to the polyunsaturated fatty acids. Also, theband at 3008 cm-1 can be the index of degree of unsaturationof sunflower oil [27]. There peaks decreases with storagetime, fact that correlate well with those obtained for iodinevalue and anisidine value. All showed the degradation ofoil during storage due to chemical change in oil structure.

Fig. 3. The iodine value (IV) for sunflower oil samples duringstorage period

Fig. 4. The anisidine value (AV) for sunflower oil samples duringstorage period

Fig. 5. The FT-IR spectra for the analysed samples

Fig. 6. HPLC-UV chromatograms of the analysed samples.

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HPLC-UV analysisA study of literature show that the HPLC method may

only give information on the different classes of partialglycerides (e.g. 1,2- and 1,3- diglycerides) [29]. In order toestablish the presence of triacylglycerides în analysedsamples was achieved by HPLC on reversed phase column.The HPLC-UV chromatograms of the all analysed samplesare presented in figure 6.

In figure 6 were observed the peaks for the mainingredients of sunflower oil, results being in agreementwith those from literature [4]. By comparing thechromatograms we notice that oleic acid peak disappearduring storage which means that it is degraded. The peaksfor saturated fatty acid are not modified during storage,while peaks for unsaturated acids modify their shape dueto the changes in molecular structure of the oil duringstorage time, the result being the same as those previouslypresented at the iodine value, anisidine value and FT-IRanalysis.

ConclusionsThis study evaluated the changes in the chemical

compositions of sunflower oil commercially available.During storage (48 months) an increasing in the values ofquality parameters FFA and AV took place that are themeasures of oxidative degradation of oils. The oxidativestability of the sunflower oil samples stored at roomtemperature was high.

However, the acidity of the sunflower oil which waswithin the limit increases very little in during storage period.It was concluded that while the initial quality of oil sampleswas good, it keep decreasing during storage, reaching theworst level after 48 months storage. The results are verifiedby using spectrometric methods FTIR and HPLC-UV. Thespectra and chromatograms registered are in accordancewith information obtained by the quantitativedeterminations.

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Manuscript received: 5.05.2015