Food Sci. Technol. Res., 15 (5), 519–524, 2009

Physicochemical Changes in Hazelnut, Olive Pomace, Grapeseed and Sunflower Oils

Heated at Frying Temperatures

* Leyla Tekin, Mehmet Seçkin Aday and Emin Yılmaz

Çanakkale Onsekiz Mart University, Faculty of Engineering and Architecture, Department of Food Engineering, Terzioglu Campus, 17020, Çanakkale, Turkey.

Received December 4, 2008; Accepted June 2, 2009

In order to compare the thermal performances to evaluate suitability for frying, hazelnut oil (HNO), olive pomace oil (OPO), grapeseed oil (GSO) and sunflower oil (SSO) were heated for 5 h / 5 consecutive days at 175 ± 5 ℃, and sampled at the end of each day. Free acidity, peroxide value, conjugated dienes, total polar materials, viscosity, and CIE color values were measured. Highest values of free acidity, conju- gated dienes, total polar materials and viscosity were observed in grapeseed oil sample. GSO has reached to a very viscous state during the earlier hours of the operation; hence it is not suitable for frying. Better thermal performances have found with HNO and OPO when compared to the control oil, SSO. Therefore, both oils can alternatively be used as new frying oils effectively.

Keywords: heating, hazelnut oil, olive pomace oil, sunflower oil, grapeseed oil, performance

Introduction 2007). In literature, many different approaches to develop Food frying is a common practice in the world, used both better frying oils and healthier fried products, and analytical in industrial scale and in small facilities as well as homes. methods have been published (Su and White, 2004; Garcia Fried foods are very popular and main items of fast-food and Valdes, 2006; Ghazali et al., 2007). Sometimes, thermal sector. By frying the surface of food yields some crispness performances of frying oils were determined by heating together with some aromatic compounds which consumers around frying temperatures without any actual food frying like most (Blumenthal, 1996). for quick screening (Shimizu et al., 2004). In frying process, the frying oil serves as a heat transfer Turkey provides around 75% of world total hazelnut medium and an ingredient of fried foods. During the process, production. In recent years, refined hazelnut oil (HNO) has heat transfer from oil to food and cooking of food, mean- become important liquid edible oil. The literature for hazel- time water vaporization from food into the oil and then to nut oil in frying is scarce. In a previous study, hazelnut oil the atmosphere, penetration of frying oil into the capillaries is heated at 121℃ in a pressure cooker and quality changes formed in food, air-oil mixing at the surface and similar phe- were monitored. Hazelnut oil was found better in stabil- nomena occur constantly. As a result of these, oil hydrolysis, ity than corn and sunflower oils (Karabulut et al., 2004). In oxidation, polymerization and Maillard reactions and some another study, potatoes were fried in microwave oven with other chemical reactions take place. The products of these hazelnut, sunflower and corn oils, and the highest fat absorp- reactions accumulate and deteriorate oil, and may develop tion was found with hazelnut oil (Şahin et al., 2007). Better toxicity in fried foods (Ghazali et al., 2007). To control fry- frying quality of virgin olive oils is rather a well established ing oil quality, guidelines have been established in many phenomenon (IOOC, 2008), but frying studies dealing with countries. In Turkey, Official Notification of the criteria to refined olive pomace (edible pomace oil) oil (OPO) is also control liquid and solid frying fats/oils rules content of po- limited. In Turkey, olive pomace oil has just become ed- lar compounds as ≤ 25%, and smoke point > 170℃ (TGK, ible oil in 2007 by officially employing the Codex Standard (Codex, 2003). In a study, characters of olive and sunflower *To whom correspondence should be addressed. oils (SSO) heated at frying temperatures were compared, E-mail: [email protected] and sunflower oil were found to be more sensitive to thermal 520 L. Tekin et al. treatment, especially viscosity of oils increased very quickly the producers. Grapeseed oil (Olitalia, Italy) was purchased (Garcia and Valdes, 2006). In another study, olive pomace from a local market. The fatty acids and main minor compo- oil was used in the search of preparing ideal frying oil mix- nents composition of the oils are provided by the producers ture compositions (Leonardi, 2005). Grapeseed oil (GSO) and shown in Table 1. All chemicals used in the analyses is a very new one for consumers. Grapeseed contains about were purchased from Merck (Darmstad, Germany) and were 7-20% oil. The hexane extracted oil has usually refined be- of analytical grade. All analyzes were duplicate in this study. fore commercial use. The oil is rich in linoleic acid (70%), Thermal treatment Thermal treatments of all frying oils phenolic compounds and tocol group compounds (Matthäus, were accomplished with a 1.5 L Cleo CLF-2500 Fryer (Kara- 2008). The generation of free radical intermediates during the köy, İstanbul) at 175 ± 5℃. First day, the fryer filled up with heating (105-108℃) of grapeseed oil has been established 1.5 L of fresh oils. Then oil sample was treated for 5 con- by a combination of spin trapping and electron paramagnetic secutive days by heating 5 h daily to total a 25 h of thermal resonance spectroscopy (Goodman et al., 1995). The effects treatment time. Sampling of oils was after the end of each of microwave and air-drying of grapeseeds on the physical day by taking 200 mL of oil into amber colored and sealed and chemical parameters of their oils were investigated. Mi- glass. Until and during the analyses oil samples were kept in crowave treatment improved oil yield and increased viscos- fridge. ity, conjugated dienes, and peroxide values while reducing Chemical analyses Total free fatty acids (FFA) of the pigment contents (K-410 and K-670 values) and p-anisidine samples were measured by titrating 1 g sample dissolved in and saponification values (Mazza et al., 1998). There is no 95% ethanol against phenolphthalein indicator according to published study with grapeseed oil in frying. On the other AOCS method Ca 5a-40 (AOCS, 1997a), and results are giv- hand, many studies with sunflower seed oil in frying opera- en as oleic acid (%). Peroxide value (PV) was determined by tions can be found elsewhere. reacting sample dissolved in a mixture of chloroform-acetic Since different oils have very diverse fatty acid and mi- acid (2:3) with a solution of potassium iodide in darkness, nor components composition, it is expected that they would then free iodine titration with a sodium thiosulfate solution behave very differently at higher temperatures. The aim of according to AOCS method Cd 8-53 (AOCS, 1997b). The this study was to compare the physicochemical changes in results were expressed as milliequivalents of active oxygen hazelnut oil (HNO), olive pomace oil (OPO), sunflower oil per kilogram of oil (meq O2 / kg sample). Conjugated diene (SSO) and grapeseed oil (GSO) heated at around 175 ± 5℃ (CD) values of the samples were determined as per AOCS Ti for 25 h in 5 consecutive days. 1a-64 (AOCS, 1997c) method. Oil samples were dissolved in iso-octane and diluted when necessary. The absorbance Materials and Methods was then measured at 233 nm, and %CD was calculated Materials In this study, the commercial refined hazelnut by the given equation. Direct reading of total polar materi- oil (Ordu Oil Co., Ordu, Turkey), refined olive pomace oil als (% TPM) was accomplished by immersing the probe of (Marbil Oil Co., İzmir, Turkey), refined-winterized sunflower Testo 265 sensor (Lenzkirch, Germany) into the oil samples seed oil (Aymar Oil Co., İstanbul, Turkey) were donated by at 45℃ according to the instructions of the instrument. The

Table 1. The fatty acids and main minor components composition of the oil samples provided by the producers. HNO OPO SSO GSO Fatty acid composition (%) Myristic (C14:0), max 0.03 < 0.05 0.06 0.05 Palmitic (C16:0) 5.34 7.5-20 5.94 8.56 Palmitoleic (C16:1), max 0.18 0.3-3.5 0.11 0.18 Heptadecenoic (C17:1), max 0.07 < 0.3 0.03 0.04 Stearic (C18:0) 2.61 0.5-5.00 3.77 4.41 Oleic (C18:1) 81.62 55-83 29.81 22.00 Linoleic (C18:2) 9.71 3.5-21 58.78 64.07 Linolenic (C18:3), max 0.09 < 0.9 0.13 0.32 Arachidic (C20:0) 0.12 < 0.6 0.25 0.15 Gadoleic (C20:1), max 0.17 < 0.4 0.16 0.15 Behenic (C22:0) 0.02 < 0.2 0.65 0.02 Total Sterols (mg/kg) 1200-2000 > 1800 2400-4500 5000-6000 Total Tocopherol (mg/kg) 250-500 trace 400-900 100-300 Thermal Stability of Oils 521 instrument can estimate total polar materials in frying fats at frying oil samples at the 0 and 25th hours of thermal treat- 40-210℃ by ±2% reliance. The instrument was calibrated to ment for the chemical and physical measurements, and the measure TPM in 0.5-40% range by ±2% accuracy with the significant differences among the days of heating (0-25 h) for standard oil provided. Above the calibration range, reading each oil per each measurement were determined by one-way can still be obtained but accuracy may change as the user’s analysis of variance using the Duncan’s multiple range com- manual indicated. parison at 95% of confidence. In addition, correlation coef- Physical analyses Refractive index of the frying oil ficients of the measured oil parameters for all samples were samples were measured under daylight with a 2WAJ model determined. The data analysis was carried out with Minitab Abbe refractometer, calibrated against pure water at 25℃ (ver. 15) and SPSS (ver. 10.1) package programs (Minitab, (AOCS, 1997d). Viscosity measurements of the frying oils 1995; SPSS, 1994). were carried out by placing 7.5 ml of sample in a special sample holder, and direct measuring centipoises (cP) reading Results and Discussion with a Brookfield viscosimeter (model DV II+Pro with Rheo- The main composition data of the oil samples are pro- calc software, Brookfield Eng. Lab., Inc., MA, US) equipped vided by the producers and shown in Table 1 for comparison with LV-SC4-18 spindle at 25℃ (Yılmaz et al., 2008). Col- and discussion purposes. Chemical changes in the heated ors of the frying oils were measured with a Minolta CR-400 oils were shown in Table 2. For each oil sample, measured Chroma Meter (Minolta, Japan) having an 8 mm diameter chemical changes were compared over heating time within viewing area. First, the instrument was calibrated against each column. In addition at the beginning (0 h) and end (25th standard white tile. Then oil samples were placed in a Petri h) of the heating treatments, the four oil samples were com- dish and the probe immersed and readings were recorded in pared among themselves for all the measured quality indices the CIE units of L value [L = 0 (black), L = 100 (white)], a* within the rows shown in the tables. In all samples, the free value (+a* = red, -a* = green), and b* value (+b* = yellow, acidity (% oleic acid) has increased by the thermal treatment -b* = blue) (Pagliarini and Rastelli, 1994). time significantly. Enhancement in free acidity (FFA) by Statistics All measurements were two parallels in this heating was 609% in grapeseed oil (GSO), the highest, and study. Significant differences among the means of the four 51.5% in hazelnut oil (HNO), the lowest. Free acidity in fry-

Table 2. Chemical changes in the four oil samples during heating five hours daily by five consecutive days. Time (h) HNO OPO SSO GSO FFA (%) 0 0.33 ± 0 D*, a** 0.34 ± 0 E, a 0.17 ± 0 D, c 0.22 ± 0 F, b 5 0.39 ± 0 C 0.88 ± 0.02 D 0.22 ± 0 C 0.66 ± 0.02 E 10 0.41 ± 0.01 C 1.12 ± 0 C 0.27 ± 0 B 0.95 ± 0 D 15 0.45 ± 0 B 1.23 ± 0 B 0.28 ± 0 B 1.21 ± 0.02 C 20 0.46 ± 0 B 1.44 ± 0.02 A 0.33 ± 0.02 A 1.44 ± 0.02 B 25 0.50 ± 0 A, c 1.46 ± 0 A, b 0.35 ± 0.02 A, d 1.56 ± 0 A, a D, b C, b C, a B, b PV (meqO2/kg) 0 1.02 ± 0.23 0.66 ± 0 1.84 ± 0.19 0.66 ± 0 5 1.84 ± 0.18 C 0.67 ± 0 C 4.06 ± 0.47 B 1.23 ± 0.23 AB 10 2.00 ± 0 BC 1.17 ± 0.18 BC 4.45 ± 0.46 AB 1.33 ± 0 AB 15 2.55 ± 0.22 AB 1.33 ± 0 AB 4.65 ± 0.005 AB 1.88 ± 0.23 A 20 2.66 ± 0 A 1.34 ± 0 AB 4.67 ± 0 AB 1.89 ± 0.23 A 25 2.67 ± 0.005 A, b 1.84 ± 0.18 A, b 5.87 ± 0.23 A, a 1.89 ± 0.23 A, b CD (%) 0 0.09 ± 0 E, c 0.13 ± 0.01 E, b 0.24 ± 0 E, a 0.15 ± 0 F, b 5 0.20 ± 0.005 D 0.21 ± 0 D 0.53 ± 0.01 D 0.71 ± 0.01 E 10 0.21 ± 0.005 D 0.32 ± 0 C 0.53 ± 0.01 D 0.90 ± 0.005 D 15 0.39 ± 0 C 0.36 ± 0 B 0.80 ± 0.005 C 1.08 ± 0.005 C 20 0.63 ± 0.005 B 0.37 ± 0 B 0.91 ± 0.02 B 1.17 ± 0.005 B 25 0.71 ± 0.005 A, c 0.56 ± 0 A, d 0.98 ± 0.01 A, b 1.39 ± 0.005 A, a TPM (%) 0 9.75 ± 0.25 F, b 7.25 ± 0.25 F, c 11.75 ± 0.25 F, a 9.00 ± 0.50 F, b 5 13.75 ± 0.25 E 12.25 ± 0.25 E 15.25 ± 0.25 E 18.25 ± 0.25 E 10 17.25 ± 0.25 D 22.50 ± 0.25 D 18.25 ± 0.25 D 41.25 ± 0.25 D 15 21.25 ± 0.25 C 26.25 ± 0.25 C 22.25 ± 0.25 C 52.25 ± 0.25 C 20 25.25 ± 0.25 B 30.25 ± 0.25 B 27.25 ± 0.25 B 65.75 ± 0.25 B 25 28.75 ± 0.25 A, d 32.75 ± 0.25 A, b 26.25 ± 0.25 A, c 77.75 ± 0.25 A, a * Means with different uppercase letter within a column indicate significant differences (P < 0.01). ** Means with different lowercase letter within a row indicate significant differences (P < 0.01). 522 L. Tekin et al. ing oils increase due to both hydrolytic reactions and thermal (Matthäus, 2008). The sensor (Testo 265) read %TPM values breakdown of the triglycerol structures. Free fatty acid levels of the frying oils were also shown in Table 2. At the 3rd. day above 1.0% in fresh frying oils is usually undesirable, since of frying, the sensor read value of grapeseed oil (41%) has excessive smoke and enhanced fat absorption occur. In lit- already exceeded the calibration range of the instrument, but erature of frying, very similar results of changes in FFA over further readings were taken to get an insight. At the 25 h of time have been reported (Shimizu et al., 2004; Mariod et al., thermal treatment, the TPM of GSO has increased by around 2006; Ghazali et al., 2007). Peroxide value (PV) of the sam- 818%. The lowest enhancement (121%) was with SSO. Ac- ples was increased over thermal treatment time, but not as cording to the official criteria (TGK, 2007), the TPM value sharply as the free acidity. The highest increase (240%) was of frying oils must be ≤ 25%. with sunflower oil (SSO). The lower enhancement values Viscosity is a physical characterization constant mostly (151.5% each) were seen with olive pomace oil (OPO) and depending to temperature and to the compositional differenc- grapeseed oils. Although both GSO and SSO are linoleic- es of the vegetable oils. The changes in the viscosity values group oils (Table 1), higher amounts of minor components of the frying oil samples were shown in Table 3. Measured (phenolics, sterols and tocols) present in the GSO may ex- at 25℃ with a rotational type instrument, the viscosity of the plain the higher oxidative stability (Matthäus, 2008). There is frying oils has ranged between 48.50 and 236.75 centipoises no defined limitation in the peroxide value in Turkish Official (cP) values. Heating caused significant increases in viscosity Notification of the quality control criteria of frying oils. On values in the four oil samples. The largest increase (386%) the other hand, it is indicated that German Guidelines put a in viscosity was with the GSO, whereas the lowest increase limit of 10 meq O2/kg PV for frying oils (Mariod et al., 2006; (%31) was with SSO. The viscosity of all oils increased TGK, 2007). Conjugated dienes (CD) are the products of with heating times. Increase in viscosity was caused due to polyunsaturated fatty acid oxidation. Increase in the amount the formation of high molecular weight polymers. The more of conjugated dienes is proportional to the uptake of oxygen viscous the frying oil, the higher the degree of deterioration and formation of peroxides during the early stages of oxida- (Ghazali et al., 2007). In another study (Meirelles et al., tion, and to the thermal formation of oligomers and poly- 2008), dynamic viscosities (mPa.s) of different vegetable mers (Ghazali et al., 2007). In all the four frying oils, CD oil at different temperatures measured. Grapeseed oil has increased with frying time throughout the frying days. The showed 60.04 values at 20℃ and 7.78 values at 90℃. On level of CD increased around 820% through the 5 days of the other hand very rapid increase in the viscosity of GSO the heating in GSO. The lowest enhancement was with OPO was even observable by eye control in this study. There must (304%). The higher the percentage of polyunsaturated acids be very easily polymerized components in GSO. Refrac- in the oil (Table 1), the higher the levels of conjugated dienes tive index is a physical constant for liquids, and it may not formed during the thermal treatment, respectively. It is quite change easily as long as the chemical composition of the obvious that chemical breakdown reactions were very high liquid stays constant. As can be observed from Table 3, the in the grapeseed oil. GSO is very unique with the high level refractive indices of the four frying oil samples have not of linoleic acid (58-78%), and proanthocyanidin compounds changed significantly throughout heating. Also, there was no

Table 3. Physical changes in the four oil samples during heating five hours daily by five consecutive days. Time (h) HNO OPO SSO GSO Viscosity (cP) 0 60.50 ± 0.20 E*, b** 62.35 ± 0.15 F, a 55.45 ± 0.25 F, c 48.50 ± 0.20 F, d 5 60.75 ± 0.05 E 67.20 ± 0.20 E 59.40 ± 0.30 E 63.30 ± 0.10 E 10 64.45 ± 0.25 D 71.30 ± 0.30 D 61.45 ± 0.25 D 88.40 ± 0.30 D 15 68.55 ± 0.15 C 78.45 ± 0.25 C 63.45 ± 0.25 C 126.80 ± 0.10 C 20 75.30 ± 0.30 B 92.30 ± 0.20 B 70.40 ± 0.10 B 169.40 ± 0.10 B 25 80.40 ± 0.30 A, d 105.15 ± 0.15 A, b 72.65 ± 0.15 A, c 236.75 ± 0.15 A, a Refractive index 0 1.471 ± 0 A, a 1.469 ± 0 A, a 1.472 ± 0 A, a 1.475 ± 0 A, a 5 1.471 ± 0 A 1.470 ± 0 A 1.472 ± 0 A 1.476 ± 0 A 10 1.471 ± 0 A 1.470 ± 0 A 1.472 ± 0 A 1.477 ± 0 A 15 1.471 ± 0 A 1.471 ± 0 A 1.473 ± 0 A 1.478 ± 0 A 20 1.472 ± 0 A 1.471 ± 0 A 1.473 ± 0 A 1.479 ± 0 A 25 1.472 ± 0 A, a 1.472 ± 0 A, a 1.473 ± 0 A, a 1.480 ± 0 A, a * Means with different uppercase letter within a column indicate significant differences (P < 0.01). ** Means with different lowercase letter within a row indicate significant differences (P < 0.01). Thermal Stability of Oils 523 difference among the oil samples at the beginning and end of have showed very similar trends of changes with this study the thermal treatment periods for the refractive indices. (Su and White, 2004). The CIE color values of the samples were shown in Table The correlation coefficients of the measured values for 4. The luminosity (L value) of the samples was followed all four oil samples are shown in Table 5. Free acidity was almost the same pattern in all oils during the thermal treat- positively and significantly correlated with CD, TPM, vis- ment period. The L value, first increased a little, and then cosity, refractive index, a* and b* values. Significant nega- decreased. Hence, it can be said that heating caused the oils tive correlations were with PV and L values. As an important became dimmer over time. There were interesting changes deterioration parameter in frying oils, FFA is expected to in the a* values of the heated oils. In HNO and SSO, the a* yield higher correlations with the other deterioration mea- value increased in the (-) direction by heating; whereas, in sures. The unexpected correlation was with PV, a negative the OPO and GSO the value increased in the opposite (+) significant correlation. On the other hand, PV has correlated direction. As indicated before a* value shows the red-green significantly with CD value. This is usual, since both indices composition of colors (+a* = red, -a* = green). On the other measure the amount of fatty acid oxidation products. TPM hand, the b* values of all heated oil samples were increased and viscosity were correlated significantly with FFA, CD, RI, significantly on (+) direction by heating time. In literature, b* value and with themselves. This is also quite an expected the color values of different soybean oil blends during frying result since thermal breakdown of oils yields enhancements

Table 4. Instrumental color changes in the four oil samples during heating five hours daily by five consecutive days. Time (h) HNO RPO SSO GSO L value 0 73.74 ± 0.06 C, c 76.39 ± 0.05 C, a 72.50 ± 0.16 D, d 75.36 ± 0.06 B, b 5 74.15 ± 0.10 C 77.70 ± 0.27 B 81.63 ± 0.09 A 83.34 ± 0.11 A 10 74.37 ± 0.06 C 80.37 ± 0.21 A 81.82 ± 0.05 A 75.66 ± 0.10 B 15 77.36 ± 0.20 B 73.53 ± 0.19 D 77.38 ± 0.28 B 82.69 ± 0.08 A 20 79.39 ± 0.04 A 68.65 ± 0.20 E 75.59 ± 0.14 C 69.67 ± 0.30 D 25 67.48 ± 0.36 D, c 62.39 ± 0.17 F, d 73.45 ± 0.33 D, a 71.50 ± 0.07 C, b a* value 0 -2.51 ± 0.15 D, c -6.43 ± 0.09 A, a -3.46 ± 0.20 D, b -6.30 ± 0.08 B, a 5 -3.28 ± 0.17 CD -5.79 ± 0.14 A -4.06 ± 0.20 D -5.79 ± 0.01 B 10 -5.51 ± 0.19 B -6.15 ± 0.08 A -4.43 ± 0.21 CD -8.37 ± 0.19 A 15 -4.29 ± 0.16 C -3.44 ± 0.34 B -6.52 ± 0.36 AB -8.42 ± 0.19 A 20 -7.33 ± 0.33 A 0.31 ± 0.19 C -5.60 ± 0.28 BC -2.36 ± 0.09 C 25 -7.36 ± 0.13 A, a 9.24 ± 0.19 D, c -7.15 ± 0.05 A, a -0.56 ± 0.20 D, b b* value 0 8.60 ± 0.26 F, d 31.56 ± 0.22 F, a 11.60 ± 0.15 F, c 19.15 ± 0.08 E, b 5 12.55 ± 0.25 E 36.55 ± 0.23 E 14.31 ± 0.24 E 19.31 ± 0.20 E 10 25.26 ± 0.19 C 38.43 ± 0.31 D 16.20 ± 0.14 D 40.32 ± 0.12 C 15 18.28 ± 0.27 D 55.48 ± 0.39 C 23.52 ± 0.07 C 39.34 ± 0.11 D 20 28.48 ± 0.36 B 64.37 ± 0.14 B 20.54 ± 0.12 B 63.49 ± 0.15 B 25 31.32 ± 0.12 A, c 66.57 ± 0.12 A, b 31.61 ± 0.16 A, c 68.76 ± 0.09 A, a * Means with different uppercase letter within a column indicate significant differences (P < 0.01). ** Means with different lowercase letter within a row indicate significant differences (P < 0.01).

Table 5. Correlation coefficients of the physicochemical parameters measured in heated oil samples. FFA PV CD TPM Vis. RI L a* b* FFA 1 -.387** .410** .735** .737** .334* -.374** .472** .927** PV -.387** 1 .427** .026 -.097 -.053 .125 -.150 -.249 CD .410** .427** 1 .853** .727** .352* -.038 -.057 .440** TPM .735** .026 .853** 1 .941** .467** -.243 .172 .715** Vis. .737** -.097 .727** .941** 1 .439** -.320* .317* .737** RI .334* -.053 .352* .467** .439** 1 -.233 .118 .351* L -.374** .125 -.038 -.243 -.320* -.233 1 -.657** -.536** a* .472** -.150 -.057 .172 .317* .118 -.657** 1 .490** b* .927** -.249 .440** .715** .737** .351* -.536** .490** 1 ** Correlation is significant at the 0.01 level. * Correlation is significant at the 0.05 level. 524 L. Tekin et al. in FFA, CD, TPM values. These products have increased Ghazali, H.M., Abdulkarim, S.M., Long, K., Lai, O.M. and Mu- the viscosity of oil and color of oil was also changed. One hammad, S.K.S. (2007). Frying quality and stability of high-oleic important result is that luminosity (L value) was correlated Moringa oleifera seed oil in comparison with other vegetable negatively with FFA and viscosity. Similarly, a* and b* val- oils. Food Chem., 105, 1382-1389. ues were correlated negatively with L value, and positively Goodman, B.A., Vicente, L., Deighton, N., Glidewell, S.M. and with each other. This is usual since changes in both a* and Empis, J.A. (1995). In situ measurement of free radical formation b* values cause a decrease in luminosity value. during the thermal decomposition of grapeseed oil using “spin trapping” and electron paramagnetic resonance spectroscopy. Conclusion Zeitschrift für Lebensmitteluntersuchung und -Forschung A, 200, It is very interesting that GSO and SSO have very simi- 44-46. lar fatty acid composition, but have showed very different IOOC. (2008). Frying with olive oil. www.iooc.org (accessed Sep- thermal performances. As shown in Table 1, the higher to- tember 2008). copherol content in SSO may be one of the reasons. GSO Karabulut, I., Ulusoy, B.Ö. and Turan, S. (2004). Performance of has showed the highest free acidity, peroxide value, CD%, some edible oils during heating in a steam pressure cooker. J. TPM%, and viscosity values among the oil samples through Food Lipids, 11, 234-241. thermal treatment. Since the GSO has reached highly vis- Leonardi, M. (2005). New blends of frying oils. Rivista Ital. Del. cous state and peroxide value over the legal limitation at the Sus. Grasse, 82, 71-81. earlier periods of the treatment, it is found as not suitable for Mariod, A., Matthäus, B., Eichner, K. and Hussein, I.H. (2006). frying. On the other hand, HNO and OPO have performed Frying quality and oxidative stability of two unconventional oils. very satisfactorily at frying temperatures, compared to SSO. J. Amer. Oil Chem. Soc., 83, 529-538. In Turkey, sunflower oil has long been used in kitchens for Matthäus, B. (2008). Virgin grapeseed oil: is it really a nutritional both cooking and frying, traditionally. It seems that OPO can highlight? Eur. J. Lipid Sci. Technol., 110, 645-650. be an alternative source as frying oil. HNO has just emerged Mazza, G., Oomah, B.D., Liang, J. and Godfrey, D. (1998). Micro- as new oil from Turkey, can be suitably used in frying, as wave heating of grapeseed: Effect on oil quality. J. Agric. Food well. Chem., 46, 4017-4021. Meirelles, A.J.A., Ceriani, R., Paiva, F.R., Goncalves, C.B. and Ba- References tista, E.A.C. (2008). Densities and viscosities of vegetable oils of AOCS. (1997a). Free fatty acids. Official Methods and Recom- nutritional value. J. Chem. Eng. Data, 53, 1846-1853. mended Practices of the American Oil Chemists Society. Official Minitab. (1995). Minitab Statistics Software ver. 15. Phoenix Tech- Method, Ca 5a-40. nologies, US. AOCS. (1997b). Peroxide value: acetic acid-chloroform method. Pagliarini, E. and Rastelli, C. (1994). Sensory and instrumental as- Official Methods and Recommended Practices of the American sessment of olive oil appearance. Grasas y Aceites, 45, 62-64. Oil Chemists Society. Official Method, Cd 8-53. Shimizu, M., Moriwaki, J., Nishide, T. and Nakajima, Y. (2004). AOCS. (1997c). Conjugated dienoic acids. Official Methods and Thermal deterioration of diacylglycerol and triacylglycerol oils Recommended Practices of the American Oil Chemists Society. during deep-frying. J. Amer. Oil Chem. Soc., 81, 571-576. Official Method, Ti 1a-64. SPSS. (1994). SPSS Professional Statistics 10.1. SPSS Inc., Chi- AOCS. (1997d). Refractive index. Official Methods and Recom- cago, US. mended Practices of the American Oil Chemists Society. Official Şahin, S., Öztop, M.C. and Sumnu, G. (2007). Optimization of Method, Cc 7-25. microwave frying of potato slices by using Taguchi technique. J. Blumenthal, M.M. (1996). Frying technology. In ‘Bailey’s Indus- Food Eng., 79, 83-91. trial Oils and Fats Products’, vol. 3, ed. by Y.H. Hui, John Wiley TGK. (2007). Official notification of the control criteria of frying and Sons, New York, pp. 429-481. fats/oils. Turkish Food Codex no: 2007/41. CODEX. (2003). Codex Standard for Olive Oils and Olive Pomace White, P. and Su, C. (2004). Frying stability of high-oleate and Oils. Codex Stan 33-1981 (Rev.2-2003). regular soybean oil blends. J. Amer. Oil Chem. Soc., 81, 783-788. Garcia, A.B. and Valdes, A.F. (2006). A study of the evolution of Yılmaz, E., Mendeş, M. and Öğütçü, M. (2008). Sensorial and the physicochemical and structural characteristics of olive and physico-chemical characterization of virgin olive oils produced in sunflower oils after heating at frying temperatures. Food Chem., Çanakkale. J. Amer. Oil Chem. Soc., 85, 441-456. 98, 214-219.