Chemical Composition and Antioxidant Properties of Clove Leaf Essential Oil LEOPOLD JIROVETZ,* ,² GERHARD BUCHBAUER, ² IVANKA STOILOVA, ‡ ALBENA STOYANOVA, ‡ ALBERT KRASTANOV, ‡ AND ERICH SCHMIDT § Department of Clinical Pharmacy and Diagnostics, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria, Department of Essential Oils, University of Food Technology, 26 Maritza Boulevard, 4002 Plovdiv, Bulgaria, and Kurt Kitzing GmbH, Hinterm Alten Schloss 21, D-86757 Wallerstein, Germany The antioxidant activity of a commercial rectified clove leaf essential oil (Eugenia caryophyllus) and its main constituent eugenol was tested. This essential oil comprises in total 23 identified constituents, among them eugenol (76.8%), followed by -caryophyllene (17.4%), R-humulene (2.1%), and eugenyl acetate (1.2%) as the main components. The essential oil from clove demonstrated scavenging activity against the 2,2-diphenyl-1-picryl hydracyl (DPPH) radical at concentrations lower than the concentra- tions of eugenol, butylated hydroxytoluene (BHT), and butylated hydroxyanisole (BHA). This essential oil also showed a significant inhibitory effect against hydroxyl radicals and acted as an iron chelator. With respect to the lipid peroxidation, the inhibitory activity of clove oil determined using a linoleic acid emulsion system indicated a higher antioxidant activity than the standard BHT. KEYWORDS: Clove leaf essential oil; chemical composition; antioxidant properties; eugenol INTRODUCTION The clove tree [Eugenia caryophyllus (Spreng) Bullock and S. G. Harrison; syn. Syzygium aromaticum (L.) Merr., Myrta- ceae] is a perennial tropical plant. It is used as a source for obtaining an essential oil, widely applied in medicine and cosmetics. The basic constituent of the oil is eugenol (2- methoxy-4-allylphenol), to which are attributed the antimicrobial and antioxidant properties of the oil. It is also used as a flavoring agent in food and cosmetic products and has pro-oxidant and antioxidant activities (1-7). The addition of antioxidants to food products earns increasing popularity as a powerful means for extending the shelf-life of products and for decreasing the nutritional losses by preventing or slowing the oxidation process (8). The most commonly applied antioxidants in the food industry are synthetic phenols, such as butylated hydroxytoluene (BHT) and butylated hy- droxyanisole (BHA). Their safety, however, is doubtful (9, 10), and there has been a general desire to replace synthetic food additives with natural alternatives (11). Therefore, intensive research and utilization of natural antioxidants that may serve as potent candidates in combating carcinogenesis and aging processes have been done. Sources of natural antioxidants are primarily plant phenolics that may occur in all parts of the plants, such as fruits, vegetables, nuts, seeds, leaves, roots, and barks (12, 13). Plant phenolics are multifunctional and can act as reducing agents, metal chelators, and singlet oxygen quenchers (14, 15). Therefore, the aim of this study was to investigate an essential oil (rectified) of clove leaves with phenolic main compounds for their antioxidant properties to obtain further information about the above-mentioned effects. MATERIALS AND METHODS Materials. The rectified clove leaf essential oil and all reference compounds, including eugenol (see Table 1), used in this study were placed at our disposal from Kurt Kitzing Co., Wallerstein, Germany. Chemical Composition of Essential Oil: Gas Chromatograpy (GC) Analysis. GC/flame ionization detector (FID) analyses were carried out using a GC-14A with a split/splitless injector, FID and C-R6A-Chromatopac integrator (Shimadzu, Japan), a GC-3700 with FID (Varian, Germany), and C-R1B-Chromatopac integrator (Shi- madzu). The carrier gas was hydrogen (flow rate of 1.2 mL/min); injector temperature, 250 °C; detector temperature, 320 °C. The temperature program started at 40 °C during 5 min, increasing at 6 °C/min up to 280 °C for 5 min. The columns were 30 m × 0.32 mm bonded FSOT-RSL-200 fused silica, with a film thickness of 0.25 µm (Biorad, Germany), and 30 m × 0.32 mm bonded Stabilwax, with a film thickness of 0.50 µm (Restek, Bellefonte, PA). Quantification was achieved using relative percent peak area calculations (mean values of three repetitions), and compound identification was carried out partly using correlations between retention times (16-20). GC/Mass Spectrometry (MS) Analysis. For GC/MS measurements, a GC-17A with QP5000 (Shimadzu), SPME sleeve adapted to injector and Compaq-ProLinea data system (class5k software), a GC-HP5890 with HP5970-MSD (Hewlett-Packard, Palo Alto, CA), and ChemStation software on a Pentium PC (Bo ¨hm, Austria), a GCQ (Finnigan * To whom correspondence should be addressed: Department of Clinical Pharmacy and Diagnostics, University of Vienna, Pharmacy-Center, Alth- anstrasse 14, A-1090 Vienna, Austria. Telephone: ++43-1-4277-55541. Fax: ++43-1-4277-9551. E-mail: leopold.jirovetz@univie.ac.at. ² University of Vienna. ‡ University of Food Technology. § Kurt Kitzing GmbH. J. Agric. Food Chem. 2006, 54, 6303-6307 6303 10.1021/jf060608c CCC: $33.50 © 2006 American Chemical Society Published on Web 07/28/2006