Determination of Furan Fatty Acids in Extra Virgin Olive Oil Emanuele Boselli,* ,† Konrad Grob, † and Giovanni Lercker ‡ Official Food Control Authority of the Canton of Zu ¨ rich (Kantonales Labor), P.O. Box, CH-8030 Zu ¨ rich, Switzerland, and Istituto di Industrie Agrarie, Universita ` di Bologna, Via S. Giacomo 7, I-40126 Bologna, Italy The presence of 4 different furan fatty acids (F-acids) was detected in 18 samples of transmethyl- ated monovarietal extra virgin olive oil: methyl 10,13-epoxy-11,12-dimethyloctadeca-10,12-dienoate [diMeF(9,5)], methyl 12,15-epoxy-13,14-dimethyleicosa-12,14-dienoate [diMeF(11,5)] and both olefinic derivatives of diMeF(11,5) with one unsaturation on the side chains conjugated with the furan ring. Transmethylated oils were analyzed by normal phase high-performance liquid chromatography coupled on-line with capillary gas chromatography. After the gas chromatographic separation step, a more selective detection of F-acids was achieved by using a photoionization detector mounted in series with a flame ionization detector. The concentration of F-acids ranged between 50 ppb (detection limit of the method) and 2.1 ppm in the oil. The olefinic derivatives of diMeF(11,5) acids detected were not artifacts created during the sample preparation or during the chromatographic analysis. Keywords: Furan fatty acids; on-line LC-GC; photoionization detector; extra virgin olive oil; mass spectrometry; squalene INTRODUCTION Furan fatty acids (F-acids) (Figure 1) are present in plants, fishes, amphibians, reptiles, and mammals, including man (Hannemann et al., 1989). Their physi- ological role has been studied because they are also isolated in appreciable amounts in commonly used foods such as fish oil, seed oils, and butter (Guth and Grosch, 1992). In some fish F-acids can represent up to 25% of the acids in the liver lipids (Glass et al., 1975). Because they accumulate during the spawning season, a biologi- cal role of F-acids is assumed in fish. Moreover, their structure is similar to that of some prostaglandins (a five-membered ring with an alkyl chain and an alkyl carboxylic chain). Nevertheless, F-acids are not biosyn- thesized in rats (Wahl and Liebich, 1994), and their role in mammalian metabolism is still unknown. F-acids were found to prevent oxidation of linoleic acid (Okada et al., 1990) and to act as antioxidants in plants (Batna and Spiteller, 1994). A relationship seems to exist between photosynthesis and F-acid concentration in plants, because parts of the plants that are exposed to daylight show a higher content of F-acids (Hannemann et al., 1989). Furthermore, F-acids are found in some vegetables such as soybeans (Guth and Grosch, 1991) and wheat, whereas they are known to be absent (or they were only identified but not determined quantita- tively) in olives, sesame, walnut, grape seed, or sun- flower (Wahl et al., 1994). For these reasons some attention was given to the determination of F-acids as quality markers for soybean oil. Their role as precursors of a light-induced off-flavor was first reported (Guth and Grosch, 1991) but recently questioned (Kao and Wu, 1998). However, there are no references about the possible use of F-acids in the quality control of other valuable oils, such as extra virgin olive oil, because the characterization of F-acids in olive oil has not been carried out. Preseparation of F-acids from predomi- nantly straight-chain fatty acids is a critical step and renders analytical methods long and laborious. Proce- dures described in the literature are not suitable for routine analysis. They can involve a two-step urea fractionation (Guth and Grosch, 1991), hydrogenation, and thin-layer chromatography (Puchta et al., 1988) or bidimensional GC-MSD (Wahl and Liebich, 1994) for the identification. In this work a new analytical method for the determination of F-acids in edible oils (e.g., olive oils) * Author to whom correspondence should be addressed (telephone 0039 051 2099914; fax 0039 051 2099911; e-mail eboselli@agrsci.unibo.it). † Official Food Control Authority of the Canton of Zu ¨ rich. ‡ Universita ` di Bologna. Figure 1. Non olefinic and olefinic furan fatty acids 2868 J. Agric. Food Chem. 2000, 48, 2868-2873 10.1021/jf990857j CCC: $19.00 © 2000 American Chemical Society Published on Web 06/27/2000