Abstract
Virgin olive oil samples of Ayvalik and Memecik olive varieties from the Aegean region of Turkey were evaluated for their acidity, peroxide, and color values, and the volatile compounds were investigated by using solid phasemicro extraction/gas chromatography/mass spectroscopy (SPME/GC/MS). The acidity of all the samples were found to be between 0.35–1.0% oleic acid and peroxide values of the oil samples ranged between 14–52 meq/O2 kg of oil. The Y, R, and B values of the samples were between 70–73.60, 1.30–4.70, and 0–3.60, respectively. The SPME/GC/MS results have shown that hexanal (5.66–15.48%), 3 hexen 1 ol (3.12–12.1%), cis 3 hexenol (6.15–13.49%), and 9 octadecenoic acid (5.99-16.01%) were observed as the characteristic volatiles for Ayvalik variety, while trans 2 hexanal (8.65–38.09%) and 3 hexen 1 ol acetate (0.97–7.43%) were observed as the characteristic volatiles for Memecik variety.
INTRODUCTION
Olive oil obtained from fresh fruit of the olive tree (Olea europeae) is appreciated for its health beneficial properties and unique flavor. It is a complex food product containing volatile compounds that contribute to its flavor distinguishing it from other edible oils. These volatile compounds that are responsible for the flavor of olive oil, play a significant role in consumer choice.[Citation1–5] The volatile composition of olive oil is effected by the agronomic effects, such as cultivar, ripeness of the fruit, enzymes, soil type, climatic conditions, geographic origin, and technological aspects.[Citation6–9] When chemical compounds and sensory attributes are analyzed in virgin olive oil, the differences between them are basically due to olive variety[Citation10] or region-specific; Freihat et al.[Citation11] reported that oil produced from the higher altitude had a higher ratio of unsaturated to saturated fatty acid compared to oil produced at the lower altitude.
Several studies have been conducted to isolate, identify, and quantify the volatile components of virgin olive oil.[Citation12] The growing interest in virgin olive oil in international markets leads the researchers to studies on the qualitative,[Citation13,Citation14] nutritional,[Citation15,Citation16] and organoleptic[Citation10,Citation17–19] characteristics of these products. The virgin olive oils produced in different geographical regions of Turkey were compared for some common physicochemical indices and sensory properties to determine the geographic difference among the production regions.[Citation20] Many researches have been conducted to classify virgin olive oils according to origin by utilizing data regarding their volatile composition.[Citation21–23] Sensory descriptive analysis studies to cluster virgin olive oils into groups of different geographic origin[Citation10,Citation17,Citation18,Citation21] were also studied. Multivariate statistical methods were used for the classification of the sensory properties of olive oils regarding varieties.[Citation21,Citation24,Citation25]
There is little information available in the literature on the volatile composition of olive oils from Turkey. Thus, the aim of the present study was to compare different Turkish virgin olive oil samples by the characterization of their volatile compounds. A total of 30 Turkish virgin olive oil samples from Ayvalik and Memecik varieties grown in the Aegean region of Turkey (Ayvalik and Memecik varieties) were evaluated by SPME/GC/MS for volatile compounds; the other quality parameters determined were acidity, peroxide value, and color.
MATERIALS AND METHODS
Olive Oil Samples
A total of 30, 2005–2006 year production virgin olive oils from 2 olive varieties (Ayvalik—11 samples, Memecik—19 samples) grown in Turkey (Ayvalik—11 samples, Memecik—19 samples) were studied. The origin and variety of the olives used in production of olive oil samples are given in . The samples were supplied from local producers as virgin olive oil and were kept in dark rooms at room temperature prior to analysis.
Table 1 Origin and the variety of olives used in production of olive oil samples
Determination of Acidity, Peroxide Value, and Color Indices
Acidity analysis[Citation26] and peroxide value (PV) analysis[Citation27] were carried out according to the American Oil Chemists' Society (AOCS) method. The results of acidity analysis are given as oleic acid (%) and the results of PV analysis were expressed as milliequivalents of active oxygen per kilogram of oil (meq O2/kg sample). Color measurement was carried out by using Lovibond PFX 880 Automatic Tintometer (The Tintometer Ltd., Salisbury, UK) and Y (yellowness), R (redness), and B (blueness) values were determined.
SPME Extraction
The volatile compounds were extracted in duplicate by using the SPME technique.[Citation28] Polydimethylsiloxane/divinylbenzene/carboxene (PDMS/DVB/CAR) 50/ 30 μm phase thickness fiber (Supelco, Bellefonte, PA, USA) was used. A 3 ± 0.01 g of virgin olive oil sample was weighed into a 10-ml vial and sealed. Before sampling, the vials were allowed to equilibrate at 23°C ± 2 for 2 h. After equilibration, SPME fiber was exposed for 30 min to the headspace of the vial and the volatiles were then adsorbed on the fiber. Sampling was performed at 40°C. The fiber was introduced into the injection port and kept for 3 min for the desorption of volatiles.
GC/MS Analysis
Separation of the volatiles was performed by using a Hewlett-Packard HP-6890 Gas Chromatograph (Hewlett-Packard, Philadelphia, PA, USA) equipped with a fused silica capillary column HP-5 (Hewlett-Packard) 30 m × 0.25 mm ID and 0.25 μm coating thickness. The column temperature was programmed as 40°C for 3 min, 8°C/min to 200°C and held for 20 min, then 20°C/min to 280°C[Citation28] with helium as the carrier gas at 0.6 ml/min flow rate. The injector and detector temperatures were set at 270 and 280°C, respectively. Identification of the volatiles was carried out by the same conditions mentioned above by using gas chromatograph coupled to a Hewlett-Packard HP-5973 Mass Selective Detector (Hewlett-Packard) (quadropole). The electron voltage was 70 Ev and mass range was 35–350 atomic mass units.
Statistical Analysis
GC/MS and acidity, peroxide value, and color indices analysis were performed in duplicate for each sample. All data were subjected to analysis of variance (ANOVA) and Duncan test to determine significant differences (p < 0.05) among samples by using the evaluation version of SPSS 15.0 (Lead Tech. Inc., USA). Cluster Analysis and Principle Component Analysis (PCA) were performed by considering the volatiles of olive oil samples. These processings were performed with the evaluation version of XLSTAT, 2009 software (XLSTAT 11.3, Addinsoft, USA).
RESULTS AND DISCUSSION
Acidity, Peroxide Value, and Color Indices
The acidity, peroxide value, and color indices of the olive oil samples are given in . The acidity of all the samples were found to be between 0.35–1.0% oleic acid and fell within the accepted value (≤2.0%) for virgin olive oils.[Citation29] The origin and variety of the olive oils had no significant influence on acidity; this was also mentioned in a study conducted on Tunusian virgin olive oils.[Citation30]
Table 2 Acidity, peroxide value, and color indices of virgin olive oil samples
Peroxide values of the oil samples ranged from 14 to 52 meq/O2 kg of oil. The upper limit of 20 meq/O2 kg of oil for peroxide value was established for virgin olive oils.[Citation29] The oils studied in this research were supplied as virgin olive oils; however, four samples (8, 9, 10, 11) from Ayvalik and five samples (19, 20, 22, 29, 30) from Memecik variety were found to have significantly high peroxide values. In a study conducted on olive oils of Turkey, 5 out of 15 virgin olive oils from different regions of Turkey were found to be above the defined limit for the PV.[Citation20]
The Y, R, and B values of the samples were in the range of 70 to 73.60, 1.30 to 4.70, and 0 to 3.60, respectively. Measurement of color is typically used to provide information on carotene and chlorophyll content of olive oil. R value is associated with β-carotene level, whereas Y and B values are associated with chlorophyll level.[Citation31] The ANOVA has shown that olive variety had no significant (p < 0.05) effect on parameters, such as acidity, peroxide value, and color indices. As stated by Ranalli and Angerosa[Citation32] and Kiritsakis et al.,[Citation33] these parameters are basically affected by factors, such as improper handling and storage of olives.
SPME/GC/MS Analysis
SPME analysis revealed a total of 21 volatiles in Ayvalik and 22 volatiles in Memecik variety ( and ). A number of seven substances (trans-2-hexanal, 3 hexene 1 ol acetate, 3 ethyl 1,5 octadiene, nonanal, 9 octadecenoic acid, α-copaene, α-farnesene) were detected as common volatiles in both varieties. Considering the volatiles of each variety separately, hexanal, 3 hexen 1 ol, cis 3 hexenol, and 9 octadecenoic acid were relevant for Ayvalik variety, whereas, trans 2 hexanal and 3 hexen 1 ol acetate were determined relevant for Memecik variety. Pentanal, hexanal, 3 hexen 1 ol, 2 hexenal, and cis 3 hexenol were determined only in Ayvalik oils, whereas 2, 4 hexadienal, trans β-ocimene, limonene, 4, 8 dimethyl 1, 3, 7 nonatriene, 2 decenal, 2 heptanal, and α-muralene were determined in Memecik oils.
Table 3 Volatiles identified in virgin olive oils of the Ayvalik variety by SPME/GC/MS
Table 4 Volatiles identified in virgin olive oils of the Memecik variety by SPME/GC/MS
A comparison of the acidity, peroxide value, and color indices of the olive oil samples with the SPME/GC/MS results is difficult. Since no significant (p < 0.05) effect of olive variety was detected on parameters, such as acidity, peroxide value, and color indices, these parameters cannot be the determinants of the volatile compounds. Haddada et al.[Citation30] and Baccouri et al.[Citation34] stated that chemical composition of olive oils had no sgnificant influence on volatile composition of olive oils.
The cluster diagram obtained with volatiles of olive oil samples is shown on . Three main clusters were formed: cluster 1 was represented by Ayvalik variety (A1–A11), cluster 2 was represented by Memecik variety olive oil samples from M12 to M28, while Memecik variety olive oil samples M29 and M30 formed cluster 3.
Figure 1 Dendogram obtained from the cluster analysis of Ayvalik and Memecik variety olive oils.
According to PCA results, two principle components were found to explain 41.18% and 12.29% of total variation and by using the two components, a bi-plot diagram was generated (). Both cluster analysis and PCA results indicated a similar grouping and showed the difference between the samples. The first group is composed of Ayvalik variety (A1–A11) and the second group is characterized by Memecik variety (M12–M28). Moreover, the third group is composed of only two samples from Memecik variety (M29 and M30). It can be seen from the figure that there is a great difference in terms of volatile compounds characterizing the composition of these three groups. Hexanal, 3 hexen 1 ol, cis 3 hexenol, and 9 octadecenoic acid were observed as the corresponding volatiles for Ayvalik variety, while trans 2 hexanal and 3 hexen 1 ol acetate were determined as the corresponding volatiles for Memecik variety. M29 and M30 samples, which formed cluster 3, were characterized by a high amount of limonene and octanal. In a study conducted by Cavalli et al.,[Citation5] trans 2 hexanal and hexanal were detected as the major volatiles in French Cailletier olive oil samples. In another study on Tunusian virgin olive oils,[Citation30] trans 2 hexanal was found to be the major volatile followed by hexanal. Angerosa et al.[Citation6] stated that cultivar influence can be evidenced by the different amounts of C6 compounds, namely: hexanal, hexan 1 ol, hexyl acetate, trans 2 hexanal, cis 3 hexen 1 ol, 3 hexen 1 ol acetate. In a study conducted by Baccouri et al.,[Citation34] hexanol, 3 hexen 1 ol, 2 hexenal, and 2 hexen 1 ol have been reported as strongly dependent on cultivar effect.
Figure 2 PCA scatterplot of Ayvalik and Memecik variety olive oils (color figure available online).
CONCLUSION
Our results demonstrated that for acidity, peroxide value, and color indices, it is observed that variety does not have any effect on these chemical parameters. However, determination of volatiles of olive oils allowed the detection of significant differences in terms of volatile compounds characterizing Ayvalik and Memecik varieties. The results indicate that hexanal, 3 hexen 1 ol, cis 3 hexenol, and 9 octadecenoic acid were characteristic for Ayvalik variety, whereas trans 2 hexanal and 3 hexen 1 ol acetate were characteristic for Memecik variety. However, considering the influence of seasonal changes these results must be confirmed by the study of a larger number of olive oil samples from various years of production to support the results obtained by this first screening.
ACKNOWLEDGMENTS
The authors wish to acknowledge the support of E.U. Research Fund for completion of this research.
Related Research Data
REFERENCES
- ECD-GA. The olive oil sector in the European Union. 2002. http://ec.europa.eu/agriculture/ publi/fact/oliveoil/2003_en.pdf (http://ec.europa.eu/agriculture/ publi/fact/oliveoil/2003_en.pdf) (Accessed: 24 February 2007 ).
- Kanavouras , A. , Kiritsakis , A. and Hernandez , R.J. 2005 . Comparative study on volatile analysis of extra virgin olive oil by dynamic headspace and solid phase micro-extraction . Food Chemistry , 90 : 69 – 79 .
- Kasapis , S. and Boskou , D. 2001 . Rheological and sensory properties of popular Greek foodstuffs: A review . International Journal of Food Properties , 4 ( 2 ) : 327 – 340 .
- Boskou , D. 1996 . Olive oil: Chemistry and technology , 159 Champaign, IL : AOCS Press .
- Cavalli , J. , Fernandez , X. , Cuvelier , L. and Loiseau , A. 2004 . Characterisation of volatile compounds of French and Spanish virgin olive oils by HS-SPME: Identification of quality-freshness markers . Food Chemistry , 88 : 151 – 157 .
- Angerosa , F. , Servili , M. , Selvaggini , R. , Taticchi , A. , Esposto , S. and Montedoro , G.F. 2004 . Volatile compounds in virgin olive oil: Occurrence and their relationship with the quality . Journal of Chromotography A , 1054 : 17 – 31 .
- Tura , D. , Prenzler , P.D. , Bedgood , D.R. , Antolowich , M. and Robards , K. 2004 . Varietal and processing effects on the volatile profile of Australian olive oils . Food Chemistry , 84 : 341 – 349 .
- Aparicio , R. and Luna , G. 2002 . Characterisation of monovarietal virgin olive oils . European Journal of Lipid Science and Technology , 104 : 614 – 627 .
- Luna , G. , Morales , M.T. and Aparicio , R. 2006 . Characterisation of 39 varietal virgin olive oils by their volatile composition . Food Chemistry , 98 : 243 – 252 .
- Aparicio , R. , Morales , M.T. and Alonso , V. 1997 . Authentication of European virgin olive oils by their chemical compounds, sensory attributes and consumers' attitudes . Journal of Agricultural and Food Chemistry , 45 : 1076 – 1083 .
- Freihat , N.M. , Al-Shannag , A.K. and El Assi , N. 2008 . Qualitative responses of Nabali olive oil to harvesting time and altitudes at sub-humid Mediterranean . International Journal of Food Properties , 11 : 561 – 570 .
- Angerosa , F. 2002 . Influence of volatile compounds on virgin olive oil quality evaluated by analytical approaches and sensor panels . European Journal of Lipid Science and Technology , 104 : 639 – 660 .
- Jimenez , A. , Aguilera , M.P. , Beltran , G. and Uceda , M. 2006 . Application of solid-phase microextraction to virgin olive oil quality control . Journal of Chromotography A , 1121 : 140 – 144 .
- Vichi , S. , Castellote , A.I. , Pizzale , L. , Conte , L.S. , Buxaderas , S. and Lopez-Tamames , E. 2007 . The occurrence of volatile and semi-volatile aromatic hydrocarbons in virgin olive oils from North-Eastern Italy . Food Control , 18 : 1204 – 1210 .
- Oven , R.W. , Giacosa , A. , Hull , W. , Haubner , R. , Würtele , G. , Spiegelhalder , B. and Bartsch , H. 2000 . Olive-oil consumption and health: The possible role of antioxidants . Lancet , 1 : 107 – 112 .
- Tuck , K. and Hayball , P.J. 2002 . Major phenolic compounds in olive oil: Metabolism and health effects . Journal of Nutritional Biochemistry , 13 : 636 – 644 .
- Morales , M.T. , Alonso , M.V. , Rios , J.J. and Aparicio , R. 1995 . Virgin olive oil aroma: Relationship between volatile compounds and sensory attributes by chemometrics . Journal of Agricultural and Food Chemistry , 43 : 2925 – 2931 .
- Reiners , J. and Grosch , W. 1998 . Odorants of virgin olive oils with different flavor profiles . Journal of Agricultural and Food Chemistry , 46 : 2754 – 2763 .
- Lopez-Feria , S. , Cardenas , S. , Garcia-Mesa , J.A. and Valcarcel , M. 2007 . Usefulness of the direct coupling headspace-mass spectrometry for sensory quality characterization of virgin olive oil samples . Analytica Chemica Acta , 583 : 411 – 417 .
- Öğütçü , M. and Yilmaz , E. 2009 . Comparison of the virgin olive oils produced in different regions of Turkey . Journal of Sensory Studies , 24 : 332 – 353 .
- Oliveros , C.C. , Boggia , R. , Casale , M. , Armanino , C. and Forina , M. 2005 . Optimisation of a new headspace mass spectrometry instrument discrimination of different geographical origin olive oils . Journal of Chromatography A , 1076 : 7 – 15 .
- Dhifi , W. , Angerosa , F. , Serraiocco , A. , Oumar , I. , Hamrouni , I. and Marzouk , B. 2005 . Virgin olive oil aroma: Characterization of some Tunisian cultivars . Food Chemistry , 93 : 697 – 701 .
- Contini , M. and Esti , M. 2006 . Effect of the matrix volatile composition in the headspace solid-phase microextraction analysis of extra virgin olive oil . Food Chemistry , 94 : 143 – 150 .
- Karasek , P. , Planeta , J. , Ostra , E.V. , Mikesova , M. , Golias , J. , Roth , M. and Vejrosta , J. 2003 . Direct continuous supercritical fluid extraction as a novel method of wine analysis comparison with conventional indirect extraction and implications for wine variety identification . Journal of Chromatography A , 1002 : 12 – 23 .
- Risticevic , S. , Carasek , E. and Pawliszyn , J. 2008 . Headspace solid-phase microextraction–gas chromatographic–time-of-flight mass spectrometric methodology for geographical origin verification of coffee . Analytica Chimica Acta , 617 : 72 – 84 .
- AOCS1 . 1997 . Free fatty acids. Official Method, Ca 5a–40 , Champaign, IL : Official Methods and Recommended Practices of the American Oil Chemists Society .
- AOCS2 . 1997 . Peroxide value, acetic acid-chloroform method. Official Method, Cd 8–53 , Champaign, IL : Official Methods and Recommended Practices of the American Oil Chemists Society .
- Szkudlarz , S. , Jelen , H. , Wojtasiak , R. and Wasowicz , E. 2003 . Application of headspace-solid phase micro extraction and multivariate analysis for plant oils differentiation . Food Chemistry , 83 : 515 – 522 .
- EEC . 1991 . Characteristics of olive and olive pomace oils and their analytical methods. Regulation EEC/2568/91 and latter modifications . Official Journal of the European Communities , L248 : 1 – 82 .
- Haddada , F.M. , Mania , H. , Daoud , D. , Fernandez , X. , Cuvelier , L. and Zarrouk , M. 2007 . Profiles of volatile compounds from some monovarietal Tunisian virgin olive oils . Comparision with French PDO. Food Chemistry , 103 : 467 – 476 .
- Anon. Oils and fats, edible oils and fats, oleochemicals and surfactants, industrial oil and resins, liquid chemicals, transparent liquids. 2006. http://www.tintometer.com/lovibond/ DOWNLOAD.HTM (http://www.tintometer.com/lovibond/ DOWNLOAD.HTM) (Accessed: 24 February 2007 ).
- Ranalli , A and Angerosa , F. 1996 . Integral centrifuges for olive oil extraction—The qualitative characteristics of product . Journal of the American Oil Chemists Society , 73 : 417 – 422 .
- Kiritsakis , A.K. , Nanos , G.D. , Polymenoupoulos , Z. , Thomai , T. and Sfakiotakis , E.Y. 1998 . Effect of fruit storage conditions on olive oil quality . Journal of the American Oil Chemists Society , 75 : 721 – 724 .
- Baccouri , B. , Temime , S.B. , Campeol , E. , Cioni , P.L. , Daoud , D. and Zarrouk , M. 2007 . Application of solid-phase microextraction to the analysis of volatile compounds in virgin olive oils from five new cultivars . Food Chemistry , 102 : 850 – 856 .