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A study on monitoring of frying performance and
oxidative stability of cottonseed and palm oil
blends in comparison with original oils
Fatma Nur Arslan, Ayça Nesibe Şapçı, Fatma Duru & Huseyin Kara
To cite this article: Fatma Nur Arslan, Ayça Nesibe Şapçı, Fatma Duru & Huseyin Kara (2017) A study on monitoring of frying performance and oxidative stability of cottonseed and palm oil blends in comparison with original oils, International Journal of Food Properties, 20:3, 704-717, DOI: 10.1080/10942912.2016.1177544
To link to this article: https://doi.org/10.1080/10942912.2016.1177544
© 2017 Taylor & Francis Group, LLC Accepted author version posted online: 02 May 2016.
Published online: 13 Oct 2016. Submit your article to this journal Article views: 2011
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A study on monitoring of frying performance and oxidative
stability of cottonseed and palm oil blends in comparison with
original oils
Fatma Nur Arslana,b, Ayça NesibeŞapçıb, Fatma Durub, and Huseyin Karab
aDepartment of Chemistry, Faculty of Science, University of Karamanoglu Mehmetbey, Karaman, Turkey; bDepartment of Chemistry, Faculty of Science, University of Selcuk, Konya, Turkey
ABSTRACT
Blending polyunsaturated oils with highly saturated or monounsaturated oils has been studied extensively; however, in literature there is negligible informa-tion available on the blending of refined cottonseed oil with palm olein oil. Blending could enhance the stability and quality of cottonseed oil during the frying process. In the present study, the effects of frying conditions on physi-cochemical properties of the palm olein-cottonseed oil blends (1:0, 3:2, 1:1, 2:3, and 0:1, w/w) were determined and compared to the pure oils. The frying process of frozen French fries was performed in duplicate at 170 ± 5°C for 10 h without interruption. The oil degradations were characterized during deep-frying applications; peroxide, free fatty acid, and iodine value by standardized methods, fatty acid profile by using a gas chromatography-flame ionization detector, polar and polymeric compounds by using the high-performance size exclusion chromatography/evaporative light scattering detector technique. The present study clearly indicated that the oxidative and frying performances of pure palm olein oil and cottonseed oil significantly improved by blending application. Results clearly indicated that the frying performance of cottonseed oil significantly improved by the blending with palm olein oil. Except that free fatty acid content, all the physicochemical variables were significantly influ-enced by type of pure and blend oils. By increasing the proportion of palm olein oil in cottonseed oil, the levels of polyunsaturated fatty acids decreased, while saturated fatty acid content increased. The progression of oxidation was basically followed by detecting polar and polymeric compounds. The fastest increments for polar and polymeric compounds were found as 6.30% level in pure cottonseed oil and as 7.07% level in 40% cottonseed oil:60% palm olein oil blend. The least increments were detected as 5.40% level in 40% cottonseed oil:60% palm olein oil blend and 2.27% level in 50% cottonseed oil:50% palm olein oil blend. These levels were considerably below the acceptable levels recommended by the official codex. Therefore, the present study suggested that blending of cottonseed oil with palm olein oil provided the oil blends (50% cottonseed oil:50% palm olein oil and 40% cottonseed oil:60% palm olein oil, w/w) with more desirable properties for human nutrition.
ARTICLE HISTORY
Received 16 December 2015 Accepted 8 April 2016
KEYWORDS
Deep-frying; Cottonseed oil; Palm olein oil; Blending; Oxidative stability; Polar compound; Polymeric compound
Introduction
The deep-frying process is one of the most popular and complex food preparation methods, and is commonly preferred by the fast-food industry.[1,2] The process is described as more complex, because during heating at 150–190°C in the presence of atmospheric oxygen and moisture, frying oils themselves undergo a great number of physical and chemical changes. These changes occur as a
CONTACTFatma Nur Arslan nurarslan@kmu.edu.tr Department of Chemistry, Faculty of Science, University of Karamanoglu Mehmetbey, Yunus Emre Campus, Karaman 70100, Turkey.
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© 2017 Taylor & Francis Group, LLC
2017, VOL. 20, NO. 3, 704–717
consequence of the autoxidation, thermoxidation, pyrolysis, and polymerization reactions, and a wide range of undesired degradation compounds have been detected in frying oils.[3–5]The species, formation, and quantity of degradation products differ according to the several parameters of the frying process conditions.
Frying process parameters of significance are expressed as; frying oil nature, process/oil temperature, frying time, design of the fryer, and moisture content of the foodstuffs. Among these parameters; more specifically, nature/type of the frying oil acts as a heat-transfer medium and contributes to the quality of fried nutrients.[2,6]Heating in the presence of air cause a number of chemical reactions in the frying oil, which changes the composition of the frying medium and produces a degradation of products such as dimeric, polymeric, or cyclic substances. The quality of fried products is affected by that of the properties of oil and some regulations have been reported in many countries to guarantee high-quality fried foodstuffs. Limits for the degradation compounds have been established some official regulations that are limiting the degradation of fats/oils for human consumption. Therefore, the preference and proper-ties of oils used in process are very important for the quality of frying medium and fried foodstuffs, also shelf life of the food products.[1,7,8]
Refined corn, sunflower, canola, soybean, or olive oils are commonly preferred oils in the cooking and frying processes. These traditional oils, with high levels of polyunsaturated fatty acids (PUFA), are not quite proper for frying due to their fatty acid composition, iodine value (IV) characteristics, and also their higher degree of oxidation tendency.[9,10]To improve the oxidative stability/quality of the oils or to enhance their frying stability; there are ways to modify them through fractionation, inter-esterification, hydrogenation, blending, or combination of these processes.[11–13]Among these methods, the blending of different types of fats and oils has appeared as an economical way for improving their physicochemical characteristics, also enhancement in oxidative stability.[9,14,15]It has been used to modify vegetable oils to get better their physicochemical functionalities, enhance their frying/oxidative stability, and improve their preferability for fried foodstuffs. The properties of oils have been modified without changing their chemical composition by using blending procedure, but with protecting natural flavor and characteristics with nutritional values. Also, mixing different vegetable oils increases the content of natural bioactive lipids and antioxidants and gives better quality frying oils. The nutritional properties of blends are mainly based on fatty acid profile that are saturated fatty acids (SFA) to unsaturated fatty acids (USFAs) ratio, tocol and sterol content, antioxidant capacity, etc.[9,11]
To improve the oxidative/frying stability during the frying process, the use of fats/oils with low unsaturation is suitable, because the oxidation rate of these oils is much lower than the oils with PUFA. The fatty acid profile of the oils are basically responsible factor for the oxidation, also formation of undesirable compounds/flavors that lower the deliciousness of fried foods.[16,17] Modifying the fatty acid profile of the oils, that is blending procedure, is the method most commonly used to stabilize/improve the oils and to formulate new frying oils. Also, the blending of polyunsa-turated oils with sapolyunsa-turated or monosapolyunsa-turated oils is an option to adjust/improve the fatty acid profile to optimal levels for frying applications. For this purpose, blending of the palm olein oil (POO) with unsaturated oils is being preferred increasingly in frying processes due to its excellent oxidative stability. This is because of its moderately low linoleic acid content is remarkably appropriated for blending with the unsaturated oils.[18,19]POO consists 38.3% of palmitic, 42.1% of oleic, and 10.6% of linoleic acids, and it is also the leading potential source of tocols, representing 70% of tocotrienols and 30% of tocopherols. Previous studies reported that tocols, natural vitamin sources, in POO acts as an antioxidant and allows for a longer/quality shelf life for fried foodstuffs. Blending POO with unsaturated oils is used to reduce the percentage of linoleic and linolenic acids to the desirable levels.[19–21]The fatty acid profile of cottonseed oil (CSO) consists of almost 70% USFAs including 18% monounsaturated, 52% polyunsaturated, and 26% saturated. The relatively balanced level of SFAs/PUFAs ratio and tocopherol compounds also provides a degree of stability to the oil that makes it suitable for high-temperature frying applications. Therefore, products fried with refined CSO have a longer life.[16,22,23]
To the best of the researcher’s knowledge, no study has been reported on blending of POO with refined CSO to formulate new frying oils, to modify pure/original oils to get better their physico-chemical functionalities and to enhance their frying/oxidative stability. In the literature, there are some articles on the study of blending of palm, sunflower, corn, canola with other refined or cold-pressed edible oils, seed oils, food additives, or others.[9–15]In the present report, it was determined that the competence of CSO with blending of POO during deep-frying process at a temperature of 170 ± 5°C, because CSO contained almost 70% amount of USFAs and possessed a low stability to oxidation reactions. Thus, to enhance the potential of CSO, it mixed with different portions of POO to improve the frying and oxidative stability of CSO during the heating procedure.
Materials and methods
Materials, chemicals, and formulating/blending oil samples
All solvents and reagents from Merck (Darmstadt, Germany) and Sigma Aldrich (USA) companies were of the highest purity and used without further purification. The fatty acid methyl ester (FAME) standards were purchased from Sigma-Aldrich (St Louis, MO, USA). Refined, bleached, and deo-dorized (RBD) CSO and POO were purchased from local markets (Konya, Turkiye). The three oil blends were formulated by blending CSO with POO in the following proportions: (1) 40% CSO with 60% POO, (2) 50% CSO with 50% POO, and (3) 60% CSO with 40% POO. The oils were mixed to form homogeneous blends at room temperature and each one was subjected to frying protocol. Also, pure CSO and POO were used for frying as a control samples. For frying applications, frozen pre-fried French fries (Superfresh, Turkey) were purchased from local markets.
Frying procedure
For frying applications, 2 L of oil /oil blend was placed into an electric deep fryer (Oleoclean; Tefal, Rumilly, France) and operated to 170 ± 5°C. When the temperature of fryer reached the desired temperature, 8% of the frozen French fries were introduced into the oil and the lid of fryer was closed. After 8 min, the French fries were removed; after a 30 min interval, the frying operation was carried out with a new potato samples. With three different CSO/POO blends and their pure oils, five frying procedures were carried out for 10 h without interruption. To determine the performance of oil/oil blend 50 mL of oil samples were collected after each hour during the deep-frying procedures. Then, the oil samples were cooled and stored in a refrigerator in brown glass flasks to avoid further quality changes, and analyses were carried out within 36 h.
Analytical methods
Fatty acid composition analysis by gas chromatography-flame ionization detector (GC/FID) technique
Before the analysis of GC, FAME of the frying oils were prepared according to the procedure suggested by Annex XA of EEC 2568/91.[24]According to this procedure; 0.10 g of the oil sample was weighed into a tube and dissolved in 10.0 mL of hexane. Afterwards, 0.10 mL of 2 N potassium hydroxide solution prepared using methanol was added and the tube was shaken for 30 s. Then, this solution was subjected to centrifugation for 5 min, at 2500 rpm. In the final step, the upper layer of sample was transferred to a GC vial and made ready for analysis.
The fatty acid composition analysis was performed on an Agilent 6890N GC system, equipped with a FID and auto-sampler, (Agilent Technologies Inc., Wilmington, DE, USA). Ultra pure hydrogen and helium gases were used as carrier and make-up, respectively. For separations, a highly polar HP-88 cyanopropyl capillary column (100 m × 0.25 mm i.d. with a 0.2μm film thickness) was used as a stationary phase. According to the optimized method by the current authors, the
temperature of injection port and detector were maintained at 250°C. The gradient oven temperature program was set to initiate at 45°C for 4 min, then the temperature was raised to 175°C at a rate of 13°C min−1, held there for 27 min, then increased to 215°C at a rate of 4°C min−1, held there for 35 min. The FAME derivative of frying oils was injected as 1μL, in a split mode (100:1). Detection of the FAs was accomplished by comparing retention times with that of approved commercial stan-dards of FAME (Supelco 37 FAME mix standard) and results are reported as percentage of FAs.
Total polar compound (TPC) analysis by column chromatography (CC) technique
The sum of TPC of frying oils was determined using the CC technique, recommended by the official International Union of Pure and Applied Chemistry (IUPAC) method.[22,25]The method based on the separation of polar compounds from non-polar components, afterward quantification of the polar fraction by gravimetrically. In brief, in this method initially slurry of 5 g silica gel was filled into the glass column and approximately 1 g of pure sea sand was added onto silica gel surface. The frying oil (1 ± 0.01 g) was dissolved in about 10 mL of the mixture of light petroleum and diethyl ether (90:10, v/v), elution solvent A. From this sample, 5 mL was placed to the column and non-polar compounds were eluted with 60 mL of elution solvent A. Afterward, for elution of the polar components diethyl ether, elution solvent B, was passed through the silica column. The fractions were collected, their solvents were evaporated, and the amount of each fraction was determined gravimetrically. The percentage of TPCs was calculated using Eq. (1):
% Total polar compound ¼Woil sample Wnonpolar fraction
Woil sample x100 (1)
Polymeric compound analysis by high-performance size exclusion chromatography-evaporative light scattering detector (HPSEC/ELSD) technique
The polymeric compound analysis were performed using Agilent 1200 series high-performance liquid chromatography (HPLC) system consisting of an AGT-G1354A model quaternary pump with a degasser, a 380 model ELSD and an automated injector system. The temperature of columns was controlled by means of AGT-G1316B model column compartment SL, operating at 35°C. In ELSD system, the optimum nebulization and evaporation temperatures were determined as 80 and 40°C, respectively. The flow rate of nebulizer gas (ultra-pure nitrogen gas) for ELSD was set to 1.5 standard liter per minute (SLM) and detector’s gain value was set to 3.
A series of a PL-Gel 100 Å (300 × 7.5mm i.d., 5 µm) and PL-Gel 500 Å (300 × 7.5 mm i.d., 5 µm) columns with a guard column (polystyrene-divinylbenzene co-polymers; Varian, Inc., UK) and tetrahydrofuran (THF) were used as a mobile phase at a flow rate of 1 mL min−1. The frying oil sample (0.50 g) was dissolved in 10 mL of THF and 5 µL of sample was injected to the system. For identification of polymeric compounds, a standard mixture of tri-, di- and monostearin and standard reference material with a certified amount of polymeric triglycerides were used.
Peroxide value (PV) analysis
The PV of the oil samples was determined according to the standard AOCS official method Cd 8b-90.[26]This method is based on the iodometric titration quantifies the iodine produced from potassium iodide by the peroxides present in the fats and oils. PV expressed as milli-equivalents of active oxygen per kilogram of oil (meq O2/kg) and was carried out as follows; the frying oil sample (10 g) was
dissolved in 25 mL of a mixture of chloroform/acetic acid (2:3, v/v) and was left to react with 1 mL a solution of potassium iodide in the darkness for closely 3 min. Then, 30 mL of distilled water and 1–2 drops of 1% starch solution were added and the liberated iodine was titrated with a 0.02 N sodium thiosulfate solution. PV was calculated with the Eq. (2):
PV¼N:V:1000
Free fatty acid (FFA) analysis
The FFA content of the oil samples were determined according to the AOCS official method Ca 5a-40.[27] FFA values were expressed as free oleic acid percentage, in brief 1 g of oil sample was precisely weighed into an Erlenmeyer flask. Ten milliliters of ethanol (%95) was introduced to the flask with volumetric dispensers and shacked strongly. The mixture was titrated with 0.01 N NaOH to the end point when the phenolphthalein indicator changed the color. The FFA value was calculated with the Eq. (3):
FFA¼2; 82:V:100
G ; % oleic acid (3)
IV analysis
The IV of the oil samples were determined using the standard Wijs method, AOCS official method Cd 1-25[28]and the analyses were conducted in triplicate.
Statistical analysis
All measurements were carried out in duplicate and reported as means ± SD of independent trials. The data were collected and recorded by using Agilent ChemStation data processor. The statistical evaluation of results was carried out using Excel database (Microsoft, 2007) and OriginPro 8 (OriginLab, USA). The obtained data were subjected to one-way analysis of variance (ANOVA) to determine the significant differences among the samples defined at p < 0.05.
Results and discussion
Fatty acid composition analysis by GC/FID technique
Polyunsaturated/saturated fatty acid ratio (ƩPUFA/ƩSFA) of pure and blend oils used in the frying experiments are presented inTable 1. As seen fromTable 1, the changes in the fatty acid composition profile and trans fatty acid content of pure and blend frying oils were observed during continuous frying process. The main identified fatty acids were found for CSO palmitic (21.63%), oleic (17.28%), and linoleic (56.52%), while for POO palmitic (39.67%), oleic (42.10%), and linoleic (10.95%) acids. The GC/FID chromatograms obtained from qualitative analysis of fatty acid composition of CSO and POO were illustrated inFig. 1. Blending of CSO with POO non-significantly modified the concentra-tion of minor fatty acids in frying blends. Blending CSO with POO increased the SFAs, especially the palmitic and oleic acids. Obtained data indicated that the level of C18:1, C16:0 increased with increasing the POO content in the frying oil blends; while the content of C18:2 decreased as the POO content was increased. It is also noticed that the ratio of polyunsaturated to SFA ratios were significantly decreased and hence, increased the stability of the blends.
PUFAs are more susceptible to oxidation reactions, whereas SFAs are more stable, thus the ratio of ƩPUFA/ƩSFA is usually defined as the best indicators for determining the degree of oil deterioration.[15,29]It was found that there was a decrease in theƩPUFA/ƩSFA ratios, whereas the trans fatty acid content increased with a prolonged frying time in all frying applications. The percent of decreases forƩPUFA/ƩSFA ratios for the 100% CSO, 60%CSO:40%POO, 50%CSO:50%POO, 40% CSO:60%POO, 100% POO were 9.97, 4.17, 5.43, 3.53, and 1.68%, respectively. Due to frying applications, marked changes were noted in the ratios of ƩPUFA/ƩSFA for 100% CSO, 60% CSO:40%POO, and 50%CSO:50%POO blended oils. These blends have higher PUFA contents, hence their oxidative stabilities are lower than the blends of 40% CSO:60% POO and 100% POO. To define the statistical significances, one-way ANOVA and the F-test were applied and results indicated that the population means are significantly different (p < 0.05). On the other side, the contents of trans-fatty acids were regularly increased during frying time for all blends. Therefore, the
Table 1. Changes in fatty acid composition characteristics during frying process for original POO, CSO, and POO/CSO blend oils, %. Fatty acid composition changes for cottonseed oil (CSO) and palm olein oil (POO) blends and original oils %100 CSO %60 CSO + %40 POO %50 CSO + %50 POO %40 CSO + %60 POO %100 POO Time Ʃ PUFA/ Ʃ SFA Trans FA, % Ʃ PUFA/ Ʃ SFA Trans FA, % Ʃ PUFA/ Ʃ SFA Trans FA, % Ʃ PUFA/ Ʃ SFA Trans FA, % Ʃ PUFA/ Ʃ SFA Trans FA, % 0th h 3.01 ± 0.006 0.47 ± 0.003 2.88 ± 0.002 0.33 ± 0.001 1.84 ± 0.005 0.33 ± 0.001 1.70 ± 0.003 0.31 ± 0.001 1.19 ± 0.002 0.19 ± 0.001 1st h 2.97 ± 0.004 0.49 ± 0.001 2.86 ± 0.003 0.35 ± 0.001 1.83 ± 0.007 0.33 ± 0.001 1.70 ± 0.005 0.31 ± 0.001 1.19 ± 0.002 0.19 ± 0.001 2nd h 2.96 ± 0.005 0.49 ± 0.001 2.83 ± 0.003 0.35 ± 0.001 1.82 ± 0.003 0.33 ± 0.002 1.70 ± 0.003 0.32 ± 0.002 1.19 ± 0.003 0.19 ± 0.003 3th h 2.92 ± 0.005 0.49 ± 0.002 2.82 ± 0.007 0.35 ± 0.003 1.82 ± 0.003 0.33 ± 0.001 1.68 ± 0.002 0.32 ± 0.002 1.18 ± 0.004 0.19 ± 0.004 4th h 2.91 ± 0.004 0.49 ± 0.001 2.82 ± 0.005 0.35 ± 0.002 1.81 ± 0.004 0.33 ± 0.001 1.67 ± 0.001 0.32 ± 0.002 1.18 ± 0.002 0.19 ± 0.003 5th h 2.89 ± 0.002 0.49 ± 0.001 2.82 ± 0.004 0.36 ± 0.002 1.78 ± 0.002 0.33 ± 0.002 1.66 ± 0.003 0.32 ± 0.003 1.18 ± 0.002 0.19 ± 0.002 6th h 2.86 ± 0.001 0.49 ± 0.001 2.79 ± 0.004 0.36 ± 0.002 1.77 ± 0.001 0.33 ± 0.003 1.66 ± 0.003 0.32 ± 0.001 1.18 ± 0.001 0.19 ± 0.001 7 th h 2.83 ± 0.004 0.49 ± 0.001 2.79 ± 0.004 0.36 ± 0.001 1.76 ± 0.004 0.34 ± 0.003 1.65 ± 0.005 0.32 ± 0.001 1.17 ± 0.004 0.20 ± 0.001 8 th h 2.75 ± 0.003 0.49 ± 0.002 2.79 ± 0.003 0.36 ± 0.001 1.75 ± 0.005 0.34 ± 0.002 1.65 ± 0.005 0.32 ± 0.001 1.17 ± 0.003 0.20 ± 0.003 9 th h 2.74 ± 0.005 0.49 ± 0.001 2.77 ± 0.005 0.36 ± 0.001 1.74 ± 0.006 0.34 ± 0.001 1.64 ± 0.004 0.32 ± 0.002 1.17 ± 0.003 0.20 ± 0.003 10 th h 2.71 ± 0.006 0.49 ± 0.001 2.76 ± 0.006 0.36 ± 0.001 1.74 ± 0.003 0.35 ± 0.001 1.64 ± 0.002 0.32 ± 0.001 1.17 ± 0.002 0.20 ± 0.002 9.97% ↓ 4.25% ↑ 4.17% ↓ 9.09% ↑ 5.43% ↓ 6.06% ↑ 3.53% ↓ 3.23% ↑ 1.68% ↓ 5.26% ↑ Means within a column are significantly different (p < 0.05). Values are reported as means ± SD of three replicate analyses (n = 3). SFA: saturated fatty acids, PUFA: polyunsaturated fatty acids, CSO: cottonseed oil, POO: palm olein oil.
blending of high/mid-range polyunsaturated oils with more saturated oils such as palm oil types can be adjust the fatty acid contents to desired levels for frying applications.
TPC analysis by CC technique and polymeric compound analysis by HPSEC/ELSD technique
TPC content is considered as an important quality indicator because it refers to all degraded products. Polar compounds consist of degraded lipidic compounds; polymeric triacylglycerols (PTAG), oxidized-triacylglycerols (ox-TAG), oxidized-diacylglycerols (ox-DAG), oxidized-monoacylglycerols (ox-MAG), diacylglycerols (DAG), monoacylglycerols (MAG), and FFAs. These degraded compounds are formed as a result of thermal oxidation reactions or hydrolytic cleavage of triglycerides during frying/heating procedures. Several studies also reported that refined or crude vegetable oils contain considerable quantities of TPC and the level of these degradation compounds increase consistently during heating/ frying applications.[30–33]
The quality of the frying oil and medium are crucial to the nutritional quality and shelf life of the fried products. Hence, many countries have reported some regulations and recommendations content of frying oil standards for TPC and polymerized compound (PC) quantities. These values range from 23 to 29% for the TPC and 12 to 15% for total polymerized lipids.[22,32]Therefore, in this research the changes of TPC and polymeric compound contents for pure and blend oils, were determined by using IUPAC CC method and HPSEC/ELSD techniques, respectively. The contents of TPC in pure and blend oils were increased linearly with frying time (Table 2). As can be seen fromTable 2, the contents of TPC increased with the frying time and the results are agreement with previously reported data for frying fats and oils. The TPC level increased maximum 12.10% level for pure CSO, 10.60% level for blend of 60%CSO:40% POO, 11.62% level for blend of 50%CSO:50% POO, 10.90% level for blend of 40%CSO:60%POO, and 11.40% level for blend of pure POO after the 10 h frying application without interruption. Also, in order to compare the rates of TPC increment between the pure and blended oils, the raise percentages were calculated for initial and end of frying times. The fastest increment was found as 6.30% in pure CSO frying process application, while the lowest increment was detected as 5.40% in 40%CSO:60%POO blend. These results were considerably good levels compared with data from other researches. Enr ıquez-Fernandez et al.[33]reported the stability of PO and a PO⁄canola oil (CO) blends during deep-fat frying of chicken nuggets and French fries. The degradation at the end of their study resulted in TPCs of 12–13.5% for PO and 11.5–14.5% for PO/CO blend. Marco et al.[34]also reported many analytical parameters of the selected blend (sunflower/palm oil 65:35 vol/vol) during a prolonged frying process (8 h discontinuous frying without oil replenishment) in comparison to pure palm oil. The total polar components, increased faster in the blend, it showed a higher tocopherol content and a lower increment in FFAs as compared to pure palm oil. After 8 h of frying, the TPC level in palm oil (16.1%) was not significantly different from
Table 2. Changes in total polar and polymeric compound characteristics during frying process for original POO, CSO, and POO/CSO blend oils, %. Polar and polymeric compound changes for cottonseed oil (CSO) and palm olein oil (POO) blends and original oils %100 CSO %60 CSO + %40 POO %50 CSO + %50 POO %40 CSO + %60 POO %100 POO Time TPC Polymeric compound TPC Polymeric compound TPC Polymeric compound TPC Polymeric compound TPC Polymeric compound 0th h 5.80 ± 0.03 3.36 ± 0.01 5.10 ± 0.04 2.39 ± 0.02 6.14 ± 0.02 2.07 ± 0.01 5.50 ± 0.01 1.43 ± 0.01 5.30 ± 0.01 0.79 ± 0.01 1st h 3.51 ± 0.01 3.32 ± 0.03 2.08 ± 0.01 2.81 ± 0.01 0.94 ± 0.02 2nd h 6.70 ± 0.02 3.85 ± 0.02 5.60 ± 0.03 4.80 ± 0.03 6.70 ± 0.04 2.20 ± 0.03 6.20 ± 0.03 2.82 ± 0.03 6.80 ± 0.01 1.32 ± 0.02 3th h 3.86 ± 0.03 4.82 ± 0.03 2.24 ± 0.03 3.66 ± 0.02 1.54 ± 0.03 4th h 7.40 ± 0.03 4.15 ± 0.03 6.10 ± 0.03 4.93 ± 0.01 7.16 ± 0.04 2.25 ± 0.03 6.90 ± 0.03 4.36 ± 0.02 7.20 ± 0.03 1.69 ± 0.04 5th h 4.16 ± 0.04 5.20 ± 0.01 2.50 ± 0.04 5.22 ± 0.04 1.72 ± 0.01 6th h 7.90 ± 0.04 5.04 ± 0.01 6.80 ± 0.04 5.25 ± 0.02 8.19 ± 0.01 2.53 ± 0.04 7.20 ± 0.03 5.49 ± 0.03 8.10 ± 0.03 1.95 ± 0.01 7th h 5.07 ± 0.02 5.71 ± 0.02 3.72 ± 0.03 6.05 ± 0.03 2.24 ± 0.03 8th h 8.50 ± 0.04 6.40 ± 0.01 7.90 ± 0.03 5.82 ± 0.02 9.11 ± 0.03 3.77 ± 0.03 8.00 ± 0.01 6.09 ± 0.03 9.00 ± 0.03 2.62 ± 0.03 9th h 6.91 ± 0.01 5.96 ± 0.04 3.96 ± 0.01 6.96 ± 0.01 2.68 ± 0.01 10th h 12.10 ± 0.03 7.61 ± 0.01 10.60 ± 0.02 5.99 ± 0.02 11.62 ± 0.01 4.34 ± 0.02 10.90 ± 0.04 8.50 ± 0.01 11.40 ± 0.04 3.98 ± 0.02 6.30 ↑ 4.25 ↑ 5.50 ↑ 3.60 ↑ 5.48 ↑ 2.27 ↑ 5.40 ↑ 7.07 ↑ 6.10 ↑ 3.19 ↑ Means within a column are significantly different (p < 0.05) for polymeric compound analysis. Values are reported as means ± SD of three replicate analyses (n = 3). TPC: total polar compound, CSO: cottonseed oil, POO: palm olein oil.
that of the sunflower/palm oil blend (15.2%), in which, however, a faster increment from the initial value (3.7 versus 8.3% of palm oil) was observed. Thus, the TPC contents determined for pure and blend oils, were considerably below the 23–29% TPC level, recommended by the European Unity Statute and the Nutrition Codex of Turkey for frying fats and oils.
Polymeric compounds are indeed a group of components with different structures consisting of polar and non-polar polymeric lipid compounds in frying oils.[35–37] Herein, polymeric compounds were detected by the HPSEC technique with ELSD detection by using the IUPAC standard method para-meters. HPSEC methods are suitable to analyze the polymerization level of frying or heated oil samples without pre-treatment procedures. This method can be also used to detect ox-TAG, DAG, ox-DAG, MAG, ox-MAG, and FFA degradation products. HPSEC/ELSD chromatogram of polymeric compounds for %50CSO:%50POO blend by two series columns were given inFig. 2. Polymerized TAG, DAG, MAG, and fatty acids were detected by HPSEC/ELSD method and obtained data were also given inTable 2. To define the statistical significances, one-way ANOVA and F-tests were applied for polymeric compound analyses. ANOVA test results indicated that the population means are significantly different (p < 0.05). Polymeric compounds are expected to increase uniquely for pure and blend oils during frying applica-tions. Polymeric compound levels under this study were identified between maximum values at 3.98% for pure POO and 8.50% level for 40%CSO:60%POO blend oil. The fastest increment was detected for 40%CSO:60%POO blend oil as 7.07%, while the lowest increment was detected for 50%CSO:50%POO blend oil as 2.27% level. All of these values are below the limit of 12–15% for the acceptable amounts for frying fats and oils.
PV, FFA, and IV analyses by titrimetric techniques
It is well known, the PV is a measure of the content of hydroperoxides formed in fats and oils through oxidation processes. Hydroperoxides are the primary products of lipid oxidation; hence, determination of PV is used as oxidative index for the early stages of lipid oxidation in frying applications.[9,38,39] The content of FFAs also indicates the extent of oil deterioration due to hydrolysis reactions of lipids, cleavage, and oxidation of the double bonds (DBs) of unsaturated FAs. FFAs are also a good indicator of hydrolytic rancidity for frying fats and oils, and as the cycles increases the content FFA also enhanced.[39–41]Another important criterion used for evaluating the stability and quality of frying oils is IV. The IV is described as a measure of the unsaturation degree and commonly used to characterize fats and oils. A decrease in IV is consistent with decreasing the
Figure 2.HPSEC/ELSD chromatogram of polymeric compounds for %50CSO:%50 POO blend by two series columns; retention times: 25.82 min, polymeric triglycerides (PTGs); 27.22 min, triacylglycerols, and oxidized triacylglycerols (TGs and ox-TGs); 28.71 min.
number of DBs became oxidized during frying process.[38,41] Herein, efforts have been made to investigate the effects of blending of CSO with POO on the oxidative stability by performing the PV, FFA, and IV analyses. Blending of vegetable oils for frying applications has emerged as an econom-ical way of modifying the physicochemeconom-ical characteristics of vegetable oils, besides enhancement in their oxidative stabilities. The PV, FFA, and IV calculated for pure CSO, POO and their blends are given in Table 3. To identify the statistical significances, one-way ANOVA and F tests were also applied for FFA, PV and IV analyses, and ANOVA test results indicated that the population means are significantly different (p < 0.05).
As shown inTable 3, all effects of frying conditions significantly affected the contents of PV, FFA, and IV. The initial PVs of pure CSO and POO were detected as 0.63 and 0.69 meq O2/kg oil, whereas
PV of 60%CSO:40%POO, 50%CSO:50%POO, and 40% CSO:60%POO blends were detected as 1.10, 1.10, and 1.26 meq O2/kg oil. The PV clearly showed that as the frying time increased the oxidative
stability of blends and pure oils decreased. As expected, blending of CSO with POO resulted in the blends that are more stable at frying temperatures. At the end of the 10 h frying period, the PVs were detected as 0.72, 0.80, 1.46, 1.70, and 0.83 meq O2/kg for CSO blended with POO in proportion of 1:0,
3:2, 1:1, 2:3, and 0:1 (w/w), respectively. These values are less than 10 meq O2/kg, and, therefore, within
the acceptable value range for fresh/refined vegetable oils according to the codex. The changes in FFA content during frying process is also given inTable 3. As shown in this results, the content of FFA was considerably affected by the type/blend of oil and frying time. During frying process, the least and highest changes in the FFA were observed in the 50%CSO:50%POO blend oil with 0.06% incensement and 60%CSO:40%POO oil blend with 0.65% incensement, respectively. These FFA and PV data were considerably good-levels compared with data from other researches. Abdulkarim et al.[11]reported the sensory and physicochemical qualities of palm olein and sesame seed oil (SSO) blends during frying of banana chips and the changes in the blend’s physicochemical and sensory characteristics were determined. Increasing amounts of SSO (from 10 to 20, 30, and 40%) and decreasing amounts of PO (from 90, 80, 70, and 60%) in the blends, results in increase in the degree of unsaturation. FFA increased from 0.25% (90 PO:10 SSO blend) to 0.65% (60 PO:40 SSO blend). Ramadan et al.[42]also reported the correlation between physicochemical analysis and radical-scavenging activity of vegetable oil blends (a mixture [1:1, w/w] of sunflower seed oil and palm olein [SO/PO] and a mixture [1:1,wt/ wt] of CSO and palm olein [CO/PO]). The oil blends were evaluated during intermittent frying of French fries on two consecutive days for 16 h, with oil replenishing after 8 h. Continuous frying of French fries showed that across the 2 days of the frying experiment, the FFA rise was slightly higher in the CO/PO blend than in the SO/PO blend. It is also evident from this research that frying the fresh oils at up to 180°C for 8 h increased the PV of the CO/PO blend more than that of the SO/PO blend, being 8.01 and 7.75 meq/kg, respectively. As shown inTable 3, the type of oil had the most significant effect on IVs. In respect to the type of oil, blending of higher proportion of POO with CSO led to increase the IVs. As expected, the pure CSO and POO frying oils, containing the highest and least content of USFAs, showed the highest and least IVs, respectively (Table 3). This results could be explained by the presence of a higher and lower content of SFAs in pure POO and CSO. The greater the unsaturation namely high IV, the more rapid the oil tends to be oxidized, principally during heating/frying applications. A decrease in IVs was observed for pure and blend oil samples during frying. At the end of 10 h frying period, the IVs were detected as 108.69, 82.47, 80.49, 72.58, and 55.30 for CSO blended with POO in proportion of 1:0, 3:2, 1:1, 2:3, and 0:1 (w/w), respectively. This outcomes could be attributed to the destruction of DBs by several chemical reactions such as oxidation or polymerization. Therefore, during deep-frying process the decrease in IVs is in parallel with decreasing the content of DBs in USFAs.
Conclusion
The effects of frying conditions on physicochemical properties of the POO–CSO blends (1:0, 3:2, 1:1, 2:3, and 0:1, w/w) were described. The oil degradations were characterized during deep-frying
Table 3. Changes in peroxide value, free fatty acid, and iodine value characteristics during frying process for original POO, CSO, and POO/CSO blend oils, %. Peroxide value, free fatty acid, and iodine value changes for cottonseed oil (CSO) and palm olein oil (POO) blends and original oils %100 CSO %60 CSO + %40 POO %50 CSO + %50 POO Time PV FFA IV PV FFA IV PV FFA IV 0th h 0.63 ± 0.004 0.51 ± 0.001 113.72 ± 0.08 1.10 ± 0.004 0.71 ± 0.003 85.96 ± 0.02 1.10 ± 0.004 1.07 ±0.001 85.03 ±0.04 1st h 0.89 ± 0.004 0.54 ± 0.001 113.29 ± 0.04 1.24 ± 0.006 0.71 ± 0.001 85.06 ± 0.04 1.11 ± 0.004 1.09 ±0.001 84.68 ±0.04 2nd h 0.92 ± 0.006 0.62 ± 0.001 113.01 ± 0.05 1.26 ± 0.007 0.82 ± 0.001 84.92 ± 0.04 1.16 ± 0.004 1.10 ±0.002 84.53 ±0.06 3th h 0.94 ± 0.005 0.71 ± 0.002 112.11 ± 0.05 1.29 ± 0.003 0.85 ± 0.001 84.77 ± 0.03 1.22 ± 0.005 1.10 ±0.002 83.91 ±0.06 4th h 0.97 ± 0.003 0.76 ± 0.003 111.64 ± 0.07 1.30 ± 0.003 0.87 ± 0.001 84.46 ± 0.03 1.25 ± 0.005 1.10 ±0.002 83.44 ±0.03 5th h 1.07 ± 0.003 0.76 ± 0.002 111.35 ± 0.06 1.10 ± 0.003 0.93 ± 0.001 84.30 ± 0.03 1.29 ± 0.005 1.12 ±0.002 83.15±0.03 6th h 0.86 ± 0.002 0.76 ± 0.002 110.87 ± 0.06 1.08 ± 0.005 0.96 ± 0.001 83.79 ± 0.05 1.38 ± 0.004 1.12 ±0.002 82.67±0.03 7th h 0.86 ± 0.001 0.76 ± 0.001 110.23 ± 0.07 1.02 ± 0.004 1.02 ± 0.002 83.34 ± 0.05 1.44 ± 0.004 1.13 ±0.002 82.03±0.07 8th h 0.85 ± 0.001 0.77 ± 0.001 109.33 ± 0.03 0.88 ± 0.007 1.02 ± 0.001 82.82 ± 0.05 1.44 ± 0.003 1.13 ±0.001 81.77±0.04 9th h 0.78 ± 0.003 0.84 ± 0.001 108.97 ± 0.05 0.86 ± 0.004 1.27 ± 0.001 82.65 ± 0.03 1.45 ± 0.003 1.13 ±0.001 81.13±0.03 10th h 0.72 ± 0.006 0.84 ± 0.001 108.69 ± 0.03 0.80 ± 0.004 1.36 ± 0.001 82.47 ± 0.03 1.46 ± 0.006 1.13 ±0.001 80.49±0.03 0.09 ↑ 0.33 ↑ 5.03 ↓ 0.30 ↓ 0.65 ↑ 3.39 ↓ 0.36 ↑ 0.06 ↑ 4.54 ↓ %40 CSO + %60 POO %100 POO Time PV FFA IV PV FFA IV 0th h 1.26 ± 0.006 0.56 ± 0.001 80.02 ± 0.03 0.69 ± 0.004 0.77 ± 0.003 56.95 ± 0.05 1st h 1.29 ± 0.004 0.62 ± 0.002 79.63 ± 0.05 0.72 ± 0.003 0.79 ± 0.001 56.86 ± 0.06 2nd h 1.30 ± 0.004 0.62 ± 0.002 79.54 ± 0.06 0.74 ± 0.003 0.79 ± 0.001 56.67 ± 0.04 3th h 1.31 ± 0.005 0.76 ± 0.002 79.50 ± 0.03 0.75 ± 0.005 0.85 ± 0.002 56.56 ± 0.04 4th h 1.32 ± 0.005 0.79 ± 0.001 78.75 ± 0.05 0.76 ± 0.004 0.95 ± 0.002 56.47 ± 0.06 5th h 1.35 ± 0.002 0.82 ± 0.002 78.83 ± 0.05 1.03 ± 0.004 0.95 ± 0.002 56.40 ± 0.06 6th h 1.38 ± 0.002 0.82 ± 0.001 78.57 ± 0.06 1.18 ± 0.004 0.95 ± 0.003 56.31 ± 0.05 7th h 1.40 ± 0.002 0.90 ± 0.001 78.54 ± 0.03 1.09 ± 0.002 0.95 ± 0.003 56.10 ± 0.05 8th h 1.53 ± 0.005 0.93 ± 0.001 77.91 ± 0.02 0.96 ± 0.002 1.05 ± 0.004 55.51 ± 0.04 9th h 1.60 ± 0.004 0.96 ± 0.001 77.80 ± 0.05 0.88 ± 0.003 1.05 ± 0.004 55.46 ± 0.04 10th h 1.70 ± 0.006 1.04 ± 0.001 72.58 ± 0.02 0.83 ± 0.003 1.09 ± 0.004 55.30 ± 0.03 0.44 ↑ 0.48 ↑ 7.44 ↓ 0.14 ↑ 0.32 ↑ 1.65 ↓ Means within a column are significantly different (p < 0.05). Values are reported as means ± SD of three replicate analyses (n = 3). PV: peroxide value, FFA: free fatty acid, IV: iodine value, CSO: cottonseed oil, POO: palm olein oil.
processes; peroxide, FFA and IV by standardized methods, fatty acid profile by GC/FID, polar and polymeric compounds by HPSEC/ELSD technique. The present study clearly indicated that the frying performances of pure POO and CSO significantly (p < 0.05) improved by the blending application. Results clearly indicated that the frying performance of CSO significantly improved by the blending with POO. Progression of oxidation was basically followed by detecting polar and polymeric compounds. The fastest increments for polar and polymeric compounds were found as 6.30% level for pure CSO and as 7.07% level for blend oil (40%CSO:60%POO). The least increments were detected as 5.40% level for blend of 40%CSO:60%POO and 2.27% level for blend of 50% CSO:50%POO. Thus, the present study suggested that blending of CSO with POO provided the oil blends with more desirable properties for the human nutrition.
Nomenclature
CC Column chromatography CSO Cottonseed oil
DAG Diacylglycerols
ELSD Evaporative light scattering detector FAME Fatty acid methyl esters
FFA Free fatty acids
FID Flame ionization detector GC Gas chromatography
HPLC High-performance liquid chromatography HPSEC High-performance size exclusion chromatography IV Iodine value
MAG Monoacylglycerols
MUFA Monounsaturated fatty acid ox-DAG Oxidized-diacylglycerols ox-MAG Oxidized-monoacylglycerols ox-TAG Oxidized-triacylglycerols POO Palm olein oil
PTAG Polymeric triacylglycerols PUFA Polyunsaturated fatty acid PV Peroxide value
SFA Saturated fatty acid
Acknowledgments
The authors wish to thank the Selcuk University S.R.P. Coordination.
Declaration of interest
The authors declared no conflict of interest.
Funding
The research was supported by Selcuk University Coordinators of Scientific Research Project entitled“Development of
The Frying Oil Production Technologies by Formation of the Blend Oils Based on The Palm/Cottonseed Oils” with
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