Comprehensive characterization of physicochemical, thermal, compositional, and sensory properties of cold-pressed rosehip seed oil

2.1. Materials

The cold-pressed rosehip seed oil used in this study was purchased from Bade Natural (Istanbul, Turkey). The company informed us that the rosehip seeds used in the oil production were obtained from rosehip fruit harvested in the Gümüşhane region of Turkey in November 2020, and the cold-pressed oil was generated in June, 2021. The oil analyses started in our laboratory in December, 2021. Therefore, the oil was stored for almost 6 months under premium conditions before the analyses took place. All chemicals, solvents, and standards used in the analyses were of analytical or chromatographic grade and purchased from Sigma (St. Louis, MO, USA) and Merck Co. (Darmstadt, Germany). Cold-pressed rosehip seed oil is shown in Figure 1.

2.2. Physicochemical properties of the oil

Specific gravity was determined according to the AOCS Cc 10b-25 method (AOCS, 2017AOCS. 2017. Official Methods and Recommended Practice of the American Oil Chemist‘s Society (7th ed.). AOCS, Champaign, IL, USA.), specific extinction values were measured with a spectrophotometer (Shimadzu UV-1800, Shimadzu Co., Kyoto, Japan) according to the AOCS Ch 5-91 method (AOCS, 2017AOCS. 2017. Official Methods and Recommended Practice of the American Oil Chemist‘s Society (7th ed.). AOCS, Champaign, IL, USA.), and refractive index was determined by an Abbe 5 refractometer (Bellingham and Stanley, Tunbridge Wells, UK). Apparent viscosity was measured by a Brookfield DV II + Pro Viscometer (Brookfield Eng. Lab., Inc., Middleborough, MA, USA) with LV-SC4-18 spindle and 50-rpm rotation speed at room temperature. Color values (L, a*, and b*) were measured with a Minolta colorimeter CR-400 (Konica, Minolta Sensing, Osaka, Japan).

Free fatty acidity, peroxide value, p-anisidine value, iodine number, saponification number and unsaponifiable matter contents were measured according to AOCS Ca 5a-40, AOCS Cd 8b-90, AOCS Cd 18-90, AOCS Cd 1b-87, AOCS Cd 3-25, and TSE 894, respectively (TSE, 1970TSE. 1970. Yemeklik Bitkisel Yağlar-Muayene Metodları. Metot TSE 894. Resmi Gazete, Ankara, Turkey.; AOCS, 2017AOCS. 2017. Official Methods and Recommended Practice of the American Oil Chemist‘s Society (7th ed.). AOCS, Champaign, IL, USA.). The total phenolic content and antioxidant capacity of the oil were determined according to Aydeniz et al. (2014)Aydeniz B, Güneşer O, Yılmaz E. 2014. Physico-chemical, sensory and aromatic properties of cold press produced safflower oil. J. Am. Oil Chem. Soc. 91, 99-110. https://doi.org/10.1007/s11746-013-2355-4 with an Agilent 8453 UV-Vis Spectrophotometer (Waldbronn, Germany). The total carotenoid content of the oil was measured according to Franke et al. (2010)Franke S, Fröhlich K, Werner S, Böhm V, Schöne F. 2010. Analysis of carotenoids and vitamin E in selected oilseeds, press cakes and oils. Eur. J. Lipid Sci. Technol. 112, 1122-1129. https://doi.org/10.1002/ejlt.200900251 by using an Agilent 8453 UV-Vis Spectrophotometer (Waldbronn, Germany).

2.3. Thermal analyses of the oil

The thermal properties of the oil were measured with a differential scanning calorimeter (DSC, Perkin-Elmer DSC 4000, Waltham, MA). Melting and crystallization parameters of the oil were determined according to Aydeniz et al. (2014)Aydeniz B, Güneşer O, Yılmaz E. 2014. Physico-chemical, sensory and aromatic properties of cold press produced safflower oil. J. Am. Oil Chem. Soc. 91, 99-110. https://doi.org/10.1007/s11746-013-2355-4 . A 5-10 mg sample was placed into an aluminum pan, sealed hermetically, and analyzed against an empty pan. The thermal program was as follows: heating from 20 to 110 °C at a rate of 10 °C/min; cooling from 110 to −40 °C at a rate of 10 °C/min; holding at that temperature for 3 min and then heating from −40 to 50 °C at a rate of 5 °C/min. Nitrogen (99.99%) was used during analysis. The thermal parameters were calculated with Pyris 1 Manager Software.

The oxidative induction time (OIT) of the oil was determined according to Aydeniz et al. (2014)Aydeniz B, Güneşer O, Yılmaz E. 2014. Physico-chemical, sensory and aromatic properties of cold press produced safflower oil. J. Am. Oil Chem. Soc. 91, 99-110. https://doi.org/10.1007/s11746-013-2355-4 . A 5-10 mg sample was placed into an aluminum pan and analyzed against an empty pan. The thermal program was as follows: heating from 30 to 170 °C at a rate of 50 °C/min with nitrogen (99.99%) and holding at that temperature for 30 min with oxygen (99.99%). The OIT of the oil was calculated with Pyris 1 Manager Software.

2.4. Determination of the fatty acid, sterol, and tocopherol compositions

The fatty acid composition of the oil was determined according to TGK 2017/26 (2017)TGK. 2017. Türk Gıda Kodeksi Zeytinyağı ve Pirina Yağı Tebliği (Tebliğ No: 2017/26). Resmi Gazete, Ankara, Turkey.. First, fatty acid methyl esters (FAME) were prepared. 100 mg of the oil were dissolved into 2 ml heptane. Then, 0.2 ml of 2 M methanolic KOH were added and the mixture was vortexed for 30 s. Finally, the mixture was centrifuged at 6461 xg for 5 min (Sigma 2-16K, Sartorius, Germany) and the clear phase was taken into a vial for injection. The fatty acid composition was determined by a Gas Chromatograph-FID (Agilent Technologies 7890B, Palo Alto, CA, US) with a HP 88 capillary column (100 m × 0.25 mm ID × 0.2 μm film thickness, J&W Scientific Co., CA, USA). The injection volume was 0.2 μl and the injector split ratio was 1:10. Hydrogen was used as carrier gas at a flow rate of 1.7 ml/min. Hydrogen (40 ml/min) and dry air (450 ml/min) were detector gases. The inlet temperature was 250 °C and detector temperature was 280 °C. The oven temperature program was as follows: holding at 130 °C for 1 min, heating to 170 °C at a rate of 6.5 °C/min, heating to 215 °C at a rate of 2.75 °C/min and holding at that temperature for 12 min, then heating to 230 °C at a rate of 40 °C/min, holding at that temperature for 5 min. Fatty acids were identified by using a FAME standard mixture (37-components, 4-24, Supelco, Bellefonte, PA, USA).

The sterol composition was determined according to the TSE EN ISO 12228 method (TSE, 1999TSE. 1999. TSE EN ISO, 1999, International Standards Official Methods 12228:1999, Animal and Vegetable Fats and Oils-Determination of Individual and Total Sterols Contents Gas Chromatographic Method. International Organization for Standardization, Geneve, Switzerland.). First, the unsaponifiable matters were obtained, and then the sterol fractions were separated with Thin Layer Chromatography (TLC). The sterol composition was determined by Gas Chromatograph-FID (Agilent Technologies 7890B) with a DB5 capillary column (30 m × 0.25 mm ID × 0.1 μm film thickness, J&W Scientific Co). Injection volume was 1 μl and the injector split ratio was 1:100. Hydrogen was used as carrier gas at a flow rate of 0.7 ml/min. Hydrogen (30 ml/min) and dry air (400 ml/min) were detector gases. The inlet temperature was 290 °C and detector temperature was 300 °C. The oven temperature program was as follows: holding at 60 °C for 2 min, heating to 220 °C at a rate of 40 °C/min and holding at that temperature for 1 min, then heating to 310 °C at a rate of 5 °C/min, then holding at that temperature for 30 min. The sterols were identified using commercial standards.

Tocopherol composition was determined according to Grilo et al. (2014)Grilo EC, Costa PN, Gurgel CSS, Beserra AFDL, Almeida FNDS, Dimenstein R. 2014. Alpha-tocopherol and gamma-tocopherol concentration in vegetable oils. Food Sci. Technol. 34, 379-385. https://doi.org/10.1590/S0101-20612014005000031 with minor modifications. 0.5 ml oil were diluted to 5 ml with dichloromethane and analyzed by a HPLC (Shimadzu Co., Kyoto, Japan) with Inertsil SIL 100A column (250 mm× 4.6 mm× 5 μm, GL Sciences Inc., Japan) and a RF-20A fluorescent detector. A methanol:water (97:3, v/v) mixture was used as the mobile phase. Isocratic elution was used with 0.8 ml/min flow rate. Detector wavelengths were 290 and 330 nm for excitation and emission, respectively. Commercial standards were used for the identification and quantification of the tocopherols.

2.5. Determination of phenolic compounds in the oil

Approximately 3 g of oil were dissolved into 3 ml of hexane, and then 3 ml of methanol were added. After that, the mixture was centrifuged at 6461 xg for 3 minutes (Sigma 2-16K, Sartorius, Germany) and the supernatant was collected. This process was repeated three times. Then, the methanolic phase was evaporated, the residue was dissolved in 1 ml of methanol and placed into a vial for injection. The phenolic composition of the oil was analyzed by a HPLC (Shimadzu Co., Kyoto, Japan) equipped with an Agilent Eclipse XDB-C18 column (250 mm × 4.6 mm × 5 μm) and a SPD-M20A diode array detector (λmax=278nm). Acetic acid:water (3:97, v:v) (A) and methanol (B) were used as the mobile phases and flow gradients used in this analysis were as follows: 0. min 0% A, 0.1-18 min 80% A, 18-24 min 70% A, 24-30 min 67.5% A, 30-36 min 45% A, 36-40 min 0% A, 40-45 min 60% A, and 45-47 min 80% A. Column temperature was 30 °C, flow rate was 0.8 ml/min and the injection volume was 20μl. Commercial standards (Sigma-Aldrich and Fluka Chem Co., St. Louis, MO, USA) were used for the identification and quantification of the phenolic compounds.

2.6. Determination of aromatic volatile compounds in the oil

The aromatic volatile compounds in the oil were determined according to Aydeniz et al. (2014)Aydeniz B, Güneşer O, Yılmaz E. 2014. Physico-chemical, sensory and aromatic properties of cold press produced safflower oil. J. Am. Oil Chem. Soc. 91, 99-110. https://doi.org/10.1007/s11746-013-2355-4 . First, 2 g of oil were placed into an amber-colored vial and the vial was kept in a water bath at 60 °C for 30 min. Then, the volatile compounds collected at the headspace of the vial were taken with the SPME fiber coated with 75 µm carboxen/polydimethylsiloxane coating. GC-MS (Shimadzu 2010 SE) with a Restek Rtx-5Sil MS column (30 m x 0.25 mm, 0.25 μm, Fisher Scientific International, Inc., USA) was used to determine the volatile compounds. Helium was used as carrier gas with 1.61 ml/min flow rate. Injector and detector temperatures were set to 250 °C, and 70 eV ionization energy was used. The temperature program was as follows: holding at 40 °C for 2 min and heating to 250 °C at a rate of 4 °C/min. For the identification of compounds, The National Institute of Standards and Technology and Wiley Registry of Mass Spectral Data were used.

2.7. Sensory descriptive analysis of the oil

A sensory descriptive analysis of the oil was carried out through Quantitative Descriptive Analysis (QDA) (Meilgaard et al., 1991Meilgaard M, Civille GV, Carr BT. 1991. Sensory Evaluation Techniques. CRC Press, Boca Raton, FL, USA.). There were six female and six male trained panelists aged between 21 and 52. These panelists were trained for at least 10 hours on different days and in different sessions. Under the management of the panel leader, five different sensory terms were developed to describe cold-pressed rosehip seed oil. The descriptive terms and references used in this analysis are presented in Table 1. Samples were served in glasses at room temperature. A 10 cm line scale from 1 at minimum intensity to 10 at maximum intensity was used to quantify the sensory characteristics. Water, unsalted cracker, dry coffee, and expectoration cups were provided to panelists in addition to the samples.

2.8. Statistical analysis

Two different cold-pressed rosehip seed oil samples from the same production year were obtained. Each analysis for each sample was made at least in duplicate, or in triplicate. The results of the sensory analysis are presented as means with standard deviation. All other data are presented as means with standard errors.

3.1. Physicochemical properties of the oil

The physiochemical properties of the cold-pressed rosehip seed oil are presented in Table 2. Specific gravity and refractive index values depend on the fatty acid compositions of oils and vary according to the oil type. In a study about rosehip seed oil, the specific gravity value was found to be 0.927 at 20 °C (Concha et al., 2006Concha J, Soto C, Chamya R, Zúniga ME. 2006. Effect of rosehip extraction processon oil and defatted meal physicochemical properties. J. Am. Oil Chem. Soc. 83, 771-775. https://doi.org/10.1007/s11746-006-5013-2 ). The refractive index value of rosehip seed oil was measured as 1.481 and 1.478 in the studies of Concha et al. (2006)Concha J, Soto C, Chamya R, Zúniga ME. 2006. Effect of rosehip extraction processon oil and defatted meal physicochemical properties. J. Am. Oil Chem. Soc. 83, 771-775. https://doi.org/10.1007/s11746-006-5013-2 and Nino et al. (2020)Nino G, Manana G, Bochoidze I. 2020. Perspectives for the production of cosmetic oils based on the plant compionents. Архивариус 2, 101-102., respectively. Our results concur with the literature.

The viscosity of the sample at 25 °C was determined as 49.5 cP. In a study (Milic et al., 2020Milic SM, Kostic MD, Milic PS, Vucic VM, Arsic AC, Veljkovic VB, Stamenkovic OS. 2020. Extraction of oil from rosehip seed: kinetics, thermodynamics, and optimization. Chem. Eng. Technol. 43, 2373-2381. https://doi.org/10.1002/ceat.201900689 ), the viscosity of cold-pressed rosehip seed oil was measured as 89.4 cP at 20 °C. The viscosity value of the oil sample did not exactly match with the literature, probably due to differences in the measurement temperature and genotype of the rosehip seeds. The L, a*, and b* color values are presented in Table 2. There is no data in the literature for comparison. As seen in Figure 1, the oil is dark orange in color which matches with the measured color values.

The free fatty acidity and acid values are shown in Table 2. According to the codex, the acid value should be a maximum of 4.0 mg KOH/g oil for cold-pressed oils (Codex, 2012Codex. 2012. Türk Gıda Kodeksi-Bitki Adı ile Anılan Yağlar Tebliği (Tebliğ No: 2012/29). Resmi Gazete, Ankara, Turkey.). Therefore, it can be said that the acid value of the sample was near the limit value but within acceptable limits. Peroxide and p-anisidine values are used to determine primary and secondary oxidation products, respectively. According to codex, the limit for the peroxide value for cold-pressed oils is 15 meqO₂/kg oil (Codex, 2012Codex. 2012. Türk Gıda Kodeksi-Bitki Adı ile Anılan Yağlar Tebliği (Tebliğ No: 2012/29). Resmi Gazete, Ankara, Turkey.). The peroxide value of the oil was near the limit value but within acceptable limits. The peroxide value for cold-pressed rosehip seed oil was measured as 1.2 and 2.1 meqO₂/kg oil in the studies of Grajzer et al. (2015)Grajzer M, Prescha A, Korzonek K, Wojakowska A, Dziadas M, Kulma A, Grajeta H. 2015. Characteristics of rose hip (Rosa canina L.) cold-pressed oil and its oxidative stability studied by the differential scanning calorimetry method. Food Chem. 188, 459-466. https://doi.org/10.1016/j.foodchem.2015.05.034 and Tenekeci (2017)Tenekeci RN. 2017. Soğuk Pres Yöntemiyle Elde Edilen İncir Ve Kuşburnu Çekirdeği Yağlarının Özelliklerinin İncelenmesi (Master’s Thesis). Selçuk Üniversitesi Fen Bilimleri Enstitüsü, Konya, Turkey., respectively. These peroxide values are much lower than the value in our study. In our study, the p-anisidine value was measured as 3.35. In a study by (Grajzer et al., 2015Grajzer M, Prescha A, Korzonek K, Wojakowska A, Dziadas M, Kulma A, Grajeta H. 2015. Characteristics of rose hip (Rosa canina L.) cold-pressed oil and its oxidative stability studied by the differential scanning calorimetry method. Food Chem. 188, 459-466. https://doi.org/10.1016/j.foodchem.2015.05.034 ), p-anisidine values for cold-pressed rosehip oils from two different manufacturers were found to be 2.5 and 7.7. Specific extinction values at 232 and 270 nm are the indicators of primary and secondary oxidation products. According to codex, E232 and E270 values for extra virgin olive oil should be a maximum of 2.50 and 0.22, respectively (Codex, 2017Codex. 2017. Türk Gıda Kodeksi Zeytinyağı ve Pirina Yağı Tebliği (Tebliğ No: 2017/26). Resmi Gazete, Ankara, Turkey.). Oil types are different, but production techniques are similar; therefore, these limit values could be suitable for comparison. The oil sample in this study exceeded the limit values given in codex. Oxidation probably occurred during the storage of the seeds (before cold pressing) and during the cold-pressing process. Therefore, storage conditions should be improved.

Iodine number and saponification values are parameters which vary according to oil type. The iodine number and the saponification value for the cold-pressed rosehip oil were determined as 170.04 g I₂/100 g oil and 193.47 mg KOH/g oil, respectively. In some studies (Grajzer et al., 2015Grajzer M, Prescha A, Korzonek K, Wojakowska A, Dziadas M, Kulma A, Grajeta H. 2015. Characteristics of rose hip (Rosa canina L.) cold-pressed oil and its oxidative stability studied by the differential scanning calorimetry method. Food Chem. 188, 459-466. https://doi.org/10.1016/j.foodchem.2015.05.034 ; Milic et al., 2020Milic SM, Kostic MD, Milic PS, Vucic VM, Arsic AC, Veljkovic VB, Stamenkovic OS. 2020. Extraction of oil from rosehip seed: kinetics, thermodynamics, and optimization. Chem. Eng. Technol. 43, 2373-2381. https://doi.org/10.1002/ceat.201900689 ), the iodine number of the cold-pressed rosehip oil was measured as 160 and 157.8 g I₂/100 g oil. The saponification value was determined as 187.4 mg KOH/g oil in the study by Concha et al. (2006)Concha J, Soto C, Chamya R, Zúniga ME. 2006. Effect of rosehip extraction processon oil and defatted meal physicochemical properties. J. Am. Oil Chem. Soc. 83, 771-775. https://doi.org/10.1007/s11746-006-5013-2 and 184.2 mg KOH/g oil in the study by Milic et al. (2020)Milic SM, Kostic MD, Milic PS, Vucic VM, Arsic AC, Veljkovic VB, Stamenkovic OS. 2020. Extraction of oil from rosehip seed: kinetics, thermodynamics, and optimization. Chem. Eng. Technol. 43, 2373-2381. https://doi.org/10.1002/ceat.201900689 . Although there are some slight differences, our results generally concur with the literature.

In this study, the unsaponifiable matter content in the cold-pressed rosehip seed oil was determined as 1.37%. In one study (Concha et al., 2006Concha J, Soto C, Chamya R, Zúniga ME. 2006. Effect of rosehip extraction processon oil and defatted meal physicochemical properties. J. Am. Oil Chem. Soc. 83, 771-775. https://doi.org/10.1007/s11746-006-5013-2 ), the unsaponifiable matter content in the rosehip seed oil was found to be 1.4%. Our result concurs with the literature. Total phenolic content and total carotenoid content are shown in Table 2. It is known that phenolic compounds have various health effects and affect the sensory properties of oils (Gioxari et al., 2016Gioxari A, Kogiannou DAA, Kalogeropoulos N, Kaliora AC. 2016. Phenolic compounds: Bioavailability and health effects, in Caballero B, Finglas PM, Toldra F (Eds.) Encyclopedia of Food and Health. Academic Press, Oxford, England, 339-345. https://doi.org/10.1016/B978-0-12-384947-2.00774-1 ). The total phenolic content in rosehip seed oil was measured as 21.54 mg GA/100 g in one study (İlyasoğlu, 2014İlyasoğlu H. 2014. Characterization of rosehip (Rosacanina L.) seed and seed oil. Int. J. Food Prop. 17, 1591-1598. https://doi.org/10.1080/10942912.2013.777075 ) and 31.08 mg GA/100 g in another study (Demir et al., 2014Demir N, Yildiz O, Alpaslan M, Hayaloglu AA. 2014. Evaluation of volatiles, phenolic compounds and antioxidant activities of rose hip (Rosa L.) fruits in Turkey. LWT-Food Sci. Technol. 57, 126-133. https://doi.org/10.1016/j.lwt.2013.12.038 ). The results from this study generally concur with the literature. In this study, the total carotenoid content in the cold-pressed rosehip seed oil was measured as 46.5 mg/kg. In one study (Fromm et al., 2012Fromm M, Bayha S, Kammerer DR, Carle R. 2012. Identification and quantitation of carotenoids and tocopherols in seed oils recovered from different rosaceae species. J. Agric. Food Chem. 60, 10733-10742. https://doi.org/10.1021/jf3028446 ), the total carotenoid content in rosehip seed oil was found to be 39.15 mg/kg; while in another study (Grajzer et al., 2015Grajzer M, Prescha A, Korzonek K, Wojakowska A, Dziadas M, Kulma A, Grajeta H. 2015. Characteristics of rose hip (Rosa canina L.) cold-pressed oil and its oxidative stability studied by the differential scanning calorimetry method. Food Chem. 188, 459-466. https://doi.org/10.1016/j.foodchem.2015.05.034 ), it was determined as 36.4 mg/kg. It was observed that the carotenoid content in the sample was slightly higher, possibly due to variety or region.

The antioxidant capacity of the oil is shown in Table 2. In some studies, the antioxidant capacity of rosehip seed oil was determined as 1.77 μmol TE/g (İlyasoğlu, 2014İlyasoğlu H. 2014. Characterization of rosehip (Rosacanina L.) seed and seed oil. Int. J. Food Prop. 17, 1591-1598. https://doi.org/10.1080/10942912.2013.777075 ), 2.53 μmol TE/g (Grajzer et al., 2015Grajzer M, Prescha A, Korzonek K, Wojakowska A, Dziadas M, Kulma A, Grajeta H. 2015. Characteristics of rose hip (Rosa canina L.) cold-pressed oil and its oxidative stability studied by the differential scanning calorimetry method. Food Chem. 188, 459-466. https://doi.org/10.1016/j.foodchem.2015.05.034 ), and 1.69 μmol TE/g (Güney, 2020Güney M. 2020. Determination of fatty acid profile and antioxidant activity of Rosehip seeds from Turkey. Int. J. Agric. Environ. Food Sci. 4, 114-118. https://doi.org/10.31015/jaefs.2020.1.13 ). Compared to these studies, the antioxidant capacity of the oil sample was slightly lower.

3.2. Thermal properties of the oil

The melting and crystallization temperatures, enthalpies, and OIT of the oil are presented in Table 3. Greater amounts of saturated fatty acids are known to cause higher melting temperatures (Mayfield et al., 2015Mayfield S, Van de Walle D, Delbaere C, Shinn SE, Proctor A, Dewettinck K, Patel A. 2015. CLA-rich chocolate bar and chocolate paste production and characterization. J. Am. Oil Chem. Soc. 92, 1633-1642. https://doi.org/10.1007/s11746-015-2740-2 ). Unsaturated fatty acids were dominant in the oil, so, a lower melting point was an expected result. There is no data in the literature for direct comparison. In the study by Ramos et al. (2016)Ramos PM, Gil JM, Sanchez MCR, Gracia LMN, Navarro SH, Gil FJM. 2016. Vibrational and thermal characterization of seeds, pulp, leaves and seed oil of rosa rubiginosa. Bol. Soc. Argent. Bot. 51, 429-439. , the thermal properties of seeds, pulp, leaves and seed oil of Rosa rubiginosa were investigated. In the thermal analysis of the seeds, a peak at around -37 ºC was observed and this peak was associated with the crystallization of α-linolenic acid and linoleic acid, which are major fatty acids in the seed oil. The results of this study are similar to this study.

OIT is the time required for the onset of oil oxidation at a given temperature and it is used as an indicator of the oxidative stability of oils. The OIT of our oil sample was determined as 3.85 min at 170 °C. It is thought that the oxidative stability of the oil was low because it was rich in polyunsaturated fatty acids (Table 4). In one study, rosehip seed oils from two different manufacturers were analyzed at 140 °C and the OIT values were found as 26 min and 23 min (Grajzer et al., 2015Grajzer M, Prescha A, Korzonek K, Wojakowska A, Dziadas M, Kulma A, Grajeta H. 2015. Characteristics of rose hip (Rosa canina L.) cold-pressed oil and its oxidative stability studied by the differential scanning calorimetry method. Food Chem. 188, 459-466. https://doi.org/10.1016/j.foodchem.2015.05.034 ). The OIT value for our sample is much lower, probably, due to differences in the analysis temperatures. Clearly, this oil has low oxidative stability near frying temperatures.

3.3. Fatty acid, sterol, and tocopherol compositions of the oil

Thirteen fatty acids were determined in rosehip seed oil and the results are presented in Table 4. It was observed that rosehip seed oil contained higher amounts of unsaturated fatty acids (92.5%). Linoleic acid was determined as the major fatty acid with 51.1% and it was followed by α-linolenic acid and oleic acid with 21.4 and 19.3%, respectively. In one study (İlyasoğlu, 2014İlyasoğlu H. 2014. Characterization of rosehip (Rosacanina L.) seed and seed oil. Int. J. Food Prop. 17, 1591-1598. https://doi.org/10.1080/10942912.2013.777075 ), linoleic acid, oleic acid, and α-linolenic acid were measured as major fatty acids with 54.05, 19.50, and 19.37%, respectively. In another study (Grajzer et al., 2015Grajzer M, Prescha A, Korzonek K, Wojakowska A, Dziadas M, Kulma A, Grajeta H. 2015. Characteristics of rose hip (Rosa canina L.) cold-pressed oil and its oxidative stability studied by the differential scanning calorimetry method. Food Chem. 188, 459-466. https://doi.org/10.1016/j.foodchem.2015.05.034 ), cold-pressed rosehip seed oils from two different manufacturers were analyzed and linoleic acid, oleic acid, and α-linolenic acid were found as major fatty acids with 51.7-44.4, 16.3-14.7 and 21.5-31.8%, respectively. In general, the results concur with the literature.

The sterol composition of the cold-pressed rosehip seed oil is presented in Table 4. β-Sitosterol was determined as the major sterol with 84.6%. It was followed by Δ-5-avenasterol (3.8%), campesterol (3.7%), Δ-7-stigmastenol (2.7%), and stigmasterol (1.6%). In a study (İlyasoğlu, 2014İlyasoğlu H. 2014. Characterization of rosehip (Rosacanina L.) seed and seed oil. Int. J. Food Prop. 17, 1591-1598. https://doi.org/10.1080/10942912.2013.777075 ), β-sitosterol, Δ-5-avenasterol, campesterol and Δ-7-stigmastenol contents were measured as 544, 31.6, 23.3 and 41.4 mg/100g, respectively. In the study of Grajzer et al. (2015)Grajzer M, Prescha A, Korzonek K, Wojakowska A, Dziadas M, Kulma A, Grajeta H. 2015. Characteristics of rose hip (Rosa canina L.) cold-pressed oil and its oxidative stability studied by the differential scanning calorimetry method. Food Chem. 188, 459-466. https://doi.org/10.1016/j.foodchem.2015.05.034 , the β-sitosterol, Δ-5-avenasterol, campesterol and stigmasterol contents of the cold-pressed rosehip seed oils were found to be 5297.3-4753.3, 242.4-379.1, 192.3-205.4, and 77.9-60.2 mg/kg, respectively. The data seems to be within the ranges reported in the literature.

Tocopherols are known as oil-soluble antioxidant and sources of vitamin E. As seen in Table 4, the total tocopherol content in the oil was measured as 1082 µg/g oil. γ-Tocopherol (773.76 µg/g oil) was determined as the major tocopherol and it was followed by α-tocopherol (266.08 µg/g oil). In one study (Fromm et al., 2012Fromm M, Bayha S, Kammerer DR, Carle R. 2012. Identification and quantitation of carotenoids and tocopherols in seed oils recovered from different rosaceae species. J. Agric. Food Chem. 60, 10733-10742. https://doi.org/10.1021/jf3028446 ), the total tocopherol content in the rosehip seed oil was measured as 1099.9 mg/kg oil and γ-tocopherol was determined as the major tocopherol. In another study (Grajzer et al., 2015Grajzer M, Prescha A, Korzonek K, Wojakowska A, Dziadas M, Kulma A, Grajeta H. 2015. Characteristics of rose hip (Rosa canina L.) cold-pressed oil and its oxidative stability studied by the differential scanning calorimetry method. Food Chem. 188, 459-466. https://doi.org/10.1016/j.foodchem.2015.05.034 ), the tocopherol compositions of cold-pressed rosehip seed oils from two different manufacturers were analyzed. The total tocopherol contents in the rosehip seed oils were determined as 1124.7 and 1037.6 mg/kg oil and, γ-tocopherol was found as the major tocopherol in both oils. The tocopherol composition of the oil is similar to those reported in the literature.

3.4. Phenolic composition of the oil

The phenolic composition of cold-pressed rosehip seed oil is presented in Table 5. Fifteen types of phenolic compounds were quantified in the oil. Rosmarinic acid was the major phenolic compound with 31.38 µg/g oil. It was followed by benzoic acid, campherol, vanillin, caffeic acid, catechin, and quercetin. In one study (Grajzer et al., 2015Grajzer M, Prescha A, Korzonek K, Wojakowska A, Dziadas M, Kulma A, Grajeta H. 2015. Characteristics of rose hip (Rosa canina L.) cold-pressed oil and its oxidative stability studied by the differential scanning calorimetry method. Food Chem. 188, 459-466. https://doi.org/10.1016/j.foodchem.2015.05.034 ), the phenolic compositions of cold-pressed rosehip seed oils from two different manufacturers were analyzed. In one of the samples, p-coumaric acid was determined as the major phenolic compound, followed by vanillic acid, ferulic acid, and vanillin. In the other sample, again, p-coumaric acid was found to be the major phenolic compound, followed by vanillin, vanillic acid, and sinapinic acid. Our results are quite different from these studies, probably because of the differences in genotype of the seeds and agricultural conditions.

3.5. Aromatic volatile compounds in the oil

The aromatic volatile compounds detected in the oil are presented in Table 6. Sixty-seven aromatic volatile compounds were quantified in cold-pressed rosehip seed oil. L-Limonene, which has aroma descriptions such as orange, terpene, and pine, was detected as a major aromatic volatile compound with a ratio of 24%. It was followed by 2,4-heptadienal, (E,E) (7.58%) and hexanal (7.02%), which have aroma descriptions such as fresh, green, vegetable. Linalyl acetate (sweet, green, bergamot, lavender), beta-myrcene (peppery, terpene, spicy), and trans-2-nonenal (oily, green, cucumber) were also detected in the oil at a ratio of approximately 4%. Dominant volatile compounds in the oil concur with the descriptive terms determined with the sensory descriptive analysis.

To the best of our knowledge, there is no study in the literature about the aromatic volatile compounds in the cold-pressed rosehip seed oil. In the study of Murathan et al. (2016)Murathan ZT, Zarifikhosroshahi M, Kafkas EN. 2016. Determination of fatty acids and volatile compounds in fruits of rosehip (Rosa L.) species by HS-SPME/GC-MS and Im-SPME/GC-MS techniques. Turk. J. Agric. For. 40, 269-279. https://doi.org/10.3906/tar-1506-50 , oil was extracted from rosehip fruit with soxhlet equipment and aromatic volatile compounds were analyzed. Butanoic acid, 1,2-propanediol, α-caryophyllene and naphthalene were determined predominantly. The data on volatile aromatics would greatly contribute to the literature referring to cold-pressed rosehip oil.

3.6. Sensory descriptions of the cold pressed rosehip seed oil

The sensory descriptive terms developed for the cold-pressed rosehip seed oil are shown in Table 7. Five sensory attributes were determined for description of the cold-pressed rosehip seed oil, namely spicy, earthy, timber/kindling, raw vegetable and bitter. Timber/kindling and raw vegetable tastes/aromas were found to be relatively dominant. Generally, these results concur with the results from the aromatic volatile compounds analysis. To the best of our knowledge, for comparison, there is no study about the sensory properties of rosehip seed oil in the literature. Therefore, this study provides very important data for those who would have interest in using this oil.