ARTICLE IN PRESS JOURNAL OF FOOD COMPOSITION AND ANALYSIS Journal of Food Composition and Analysis 20 (2007) 57–62 www.elsevier.com/locate/jfca Short Communication Spectrofluorometric and high-performance liquid chromatographic determination of all-rac-a-tocopheryl acetate in virgin olive oil Il Kyu Choa, Jamil Rimab, Chiou Ling Changc, Qing X. Lia,Ã aDepartment of Molecular Biosciences and Bioengineering, University of Hawaii at Manoa, 1955 East-West Road, Honolulu, HI 96822, USA bLaboratory of Molecular Chemistry, Faculty of Science II, The Lebanese University, Fanar, P.O. Box 26110217, Lebanon cUS Pacific Basin Agricultural Research Center, 2727 Woodlawn Drive, Honolulu, HI 96822, USA Received 4 October 2005; received in revised form 21 June 2006; accepted 28 June 2006 Abstract A high-performance liquid chromatographic (HPLC) method was developed for the analysis of all-rac-a-tocopheryl acetate in olive oil. After extraction of all-rac-a-tocopheryl acetate from olive oil into hexane/ethyl acetate (4:1, v/v), it was measured with HPLC-diode array detection and regular external standard calibration and confirmed with liquid chromatography–mass spectrometry. Spectro- fluorometric and standard addition methods were also used to quantify all-rac-a-tocopheryl acetate in olive oil. A standard addition method is based on fortification of known concentrations of all-rac-a-tocopheryl acetate in a sample. The concentrations (30.47 1.2 mg/mL) of all-rac-a-tocopheryl acetate determined with the HPLC method were comparable with those (32.671.1 mg/mL) with the spectrofluorometric method. Standards were checked for linearity giving correlation coefficients of higher than 0.999 in a concentration range from 0.5 to 20 mg/mL. r 2006 Elsevier Inc. All rights reserved. Keywords: Olive oil; Tocopherol acetate; Vitamin E acetate; Vitamin E; Method 1. Introduction that of the unesterified tocopherol and is excellent for skin care (Gensler et al., 1996). Studies have shown numerous Vegetable oils, nuts, green leafy vegetables, and fortified skin benefits from the use of this vitamin (Gensler et al., cereals are common food sources of vitamin E (Rader 1996; Mayer et al., 1993; Alberts et al., 1996). All-rac-a- et al., 1997). Antioxidants such as vitamin E act to protect tocopheryl acetate is added to foods to increase vitamin E cells against the effects of free radicals that are potentially content, while a-tocopherol is a form of vitamin E in fruits. harmful in energy metabolism, and they prevent oils from Several high-performance liquid chromatographic becoming rancid during storage and thus extend oil shelf (HPLC) studies for the determination of tocopherols and life. Free radicals can damage cells and may contribute to tocopheryl acetate in virgin olive oil and in soybean oil the development of cardiovascular disease and cancer have been reported (Rader et al., 1997; Indyck, 1988; (Rader et al., 1997). Many research efforts have been made Dionisi et al., 1995; Gimeno et al., 2000a, b; Klejdus et al., to determine whether vitamin E, through its ability to limit 2004; Aoun et al., 2005; Tasioula-Margari and Okogeri, production of free radicals, might help prevent or delay the 2001). A comprehensive review on the HPLC analysis of development of these chronic diseases (Blekas et al., 1995; a-tocopherol and related compounds in biological matrices Baldioli et al., 1996; Manzi et al., 1998). The acetate form has been recently published (Rupe´rez et al., 2001). Many of vitamin E is an ester that is more stable in the presence methodological differences can influence the effectiveness of light and oxygen than tocopherol. The shelf life of all- of analysis. In general, separation of all tocopherol rac-a-tocopheryl acetate (vitamin E acetate) is greater than analogues is easier with a normal-phase HPLC system than a reversed-phase system (Mino et al., 1985; Rupe´rez ÃCorresponding author. Tel.: +1 808 956 2011; fax: +1 808 956 3542. et al., 2001; Sobczak et al., 1999; Kiyose et al., 2001; E-mail address: [email protected] (Q.X. Li). Ryyna¨nen et al., 2004; Gimeno et al., 2000a, b; Huo 0889-1575/$ - see front matter r 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jfca.2006.06.011 ARTICLE IN PRESS 58 I.K. Cho et al. / Journal of Food Composition and Analysis 20 (2007) 57–62 et al., 1999). When only a-tocopherol is to be separated GP50 gradient pump and column oven (Timberline 101) from other tocopherols and quantified, reversed-phase and controlled by Chromeleon software. The instrument HPLC is often chosen (Rupe´rez et al., 2001; Nilsson was run at the following conditions: flow rate, 2.0 mL/min; et al., 1978; Julianto et al., 1999). Methods for the analysis column temperature, 30 1C; detection wavelength, 280 nm; of tocopherol contents of erythrocytes with and without column, Inertsil ODS-2, 5 mm, 4.6 Â 250 mm2; mobile prior saponification are well described by Vatassery et al. phase, acetonitrile (ACN)/methanol (95%/5%, v/v); and (1993) and Gonzalez-Corbella et al. (1994), respectively. It injection volume, 20 mL. Retention time of all-rac-a- is suggested that quantification of b-, g-, and d-tocopherols tocopheryl acetate was 9.87 min. and tocopherolquinones could be achieved with satisfac- tory precision and accuracy only by use of a sensitive 2.3.2. Spectrofluorometric luminescence detector (Mino et al., 1985; Rupe´rez et al., 2001; Sobczak A PTI Spectrofluorometry (Photo Technology Interna- et al., 1999; Vatassery et al., 1993). For this reason, tional) was run at an excitation wavelength (lex)of295nm fluorometric or electrochemical detection was preferred to and an emission wavelength (lem) of 325 nm for all-rac-a- UV (Sobczak et al., 1999; Hewavitharana et al., 2004). tocopheryl acetate. A standard addition method (Muel and The objectives of this study were to develop a spectro- Lacroix, 1960; Rima et al., 1982) was used to calibrate fluorometric method and an HPLC method for the analysis all-rac-a-tocopheryl acetate contents in olive oils. The of a-tocopheryl acetate in olive oil without saponification, standard was all-rac-a-tocopheryl acetate added in compare the two methods, and to show the potential of the olive oil. spectrofluorometric method for the determination of all- rac-a-tocopheryl acetate in oils. 2.3.3. Liquid chromatography–mass spectrometry An Agilent 1100 series liquid chromatograph–mass 2. Materials and methods spectrometer (LC–MS) was used, consisting of a vacuum degasser, binary pump, auto-sampler, column thermostat, 2.1. Extraction of tocopherols diode array detector, and a 1100 series mass selected detector (MSD) controlled by Agilent ChemStation. An aliquot of 10 mL of 50% aqueous ethanol was added in Samples were analysed on Agilent 1100 series LC–MSD an olive oil sample (1 mL) in a 50-mL Pyrex glass tube with a with atmospheric pressure chemical ionization (APCI) Teflon screw cap. The olive oil sample was extracted three mode. The corona discharge electrode was set to 2.0 kV times with 10 mL of a mixture of n-hexane and ethyl acetate and the APCI probe temperature to 450 1C. The APCI (4:1, v/v). The tubes were shaken at a speed of 500 strokes/ heater gas (nitrogen) was set to 400 L/h, and the nebulizer min for 10 min. After being vortex-mixed and centrifuged gas (nitrogen) at 80 p.s.i. Mass spectra were recorded at a (3000g, 5 min), the extracts were combined and dehydrated scan range of 100–800m/z and the protonated molecular with a rotary evaporator at 40 1C. The residue was dissolved ions ([M+H]+) were measured (Vaule et al., 2004). The in 2 mL of n-hexane, and was filtered through a 0.45 mm [M+H]+ ions of all-rac-a-tocopheryl acetate and all-rac-a- nylon filter prior to HPLC. An amount of 1 mL of olive oil tocopherol were 473 and 431, respectively. was mixed with 9 mL of a mixture of ACN/hexane (4:1, v/v), LC-ion trap MS analyses were carried out on an and then an aliquot of 4 mL of the solution was placed UltiMateTM plus nano LC system interfaced to an Esquire directly in a cell for spectrofluorometric measurement. HCT ion trap mass spectrometer (LC/ITMS) (Bruker Daltonics, Bremen, Germany). The gradient elution was 2.2. Chemicals and reagents started at 2% ACN and 0.1% formic acid in water for 5 min, ramped to 60% ACN in 10 min, and finally to 80% All chemicals and solvents used were of analytical ACN for another 15 min. Flow rate was 150 mL/min. An reagent grade or of the highest purity available. These aliquot (5 mL) of the sample solution (in a 20 mL sample reagents included HPLC-grade acetonitrile, ethanol, loop) was injected with an auto-sampler onto a C-18 nano- methanol, and hexane (Fisher ChemiAlert), ethyl acetate, column (PepMap 100, 75 mm i.d. Â 15 cm), which was diethyl ether, and acetonitrile (Aldrich), sodium hydroxide connected to an ion source chamber (orthogonal) with a and sodium sulphate (Merck), all-rac-a-tocopheryl acetate sheath gas flow at 3 units for MS analysis and adjusted to (ICN Biomedical Inc.), and all-rac-a-tocopherol (Sigma). Expert mode (À2000 V capillary voltage of ion source, Ultra-pure water was prepared using a multi-Q filter 200 ms max. accumulation time, 3.0 L/min dry gas, 150 1C system (Millipore). Olive oil was produced from Italian- dry temp). Mass spectra were recorded at a scan range of grown olives (extra virgin olive oil). 100–1000m/z. 2.3. Equipment 2.4. Calibration curve and recovery 2.3.1.