Oxygen-18 measurement of Andalusian olive oils by continuous flow pyrolysis/isotope ratio mass spectrometry Marı ´a A. Aramendı ´a 1 , Alberto Marinas 1 * , Jose ´ M. Marinas 1 , Jose ´ M. Moreno 1 , Mustafa Moalem 1,2 , Luis Rallo 2 and Francisco J. Urbano 1 1 Department of Organic Chemistry, University of Co ´rdoba, Campus de Rabanales, Marie Curie Building, E-14014 Co ´ rdoba, Spain 2 Department of Agronomy, ETSIAM, University of Co ´rdoba, Campus de Rabanales, Celestino Mutis Building, E-14071 Co ´ rdoba, Spain Received 13 October 2006; Revised 1 December 2006; Accepted 3 December 2006 We report a method for the determination of d 18 O isotopic abundance in olive oils. The results obtained by applying the method to various Andalusian oil samples obtained in the 2004/05 and 2005/ 06 seasons are discussed in relation to olive variety, geographical origin, climate and ripeness index. Application of the method to samples of assured varietal purity exposed the influence of olive variety and origin but not of the ripeness index. The d 18 O values for the 2005/06 season are higher on average than those obtained in the colder 2004/05 season. Results obtained for samples of the Picual and Hojiblanca varieties in Co ´rdoba and Ma ´laga in the 2005/06 season suggest a correlation between enrichment in heavy isotopes and latitude whereas no clear-cut effect of altitude was observed. Copyright # 2007 John Wiley & Sons, Ltd. Olive oil, which is a major ingredient of Mediterranean diet, is said to efficiently protect against some types of cancer and coronary heart disease. 1,2 This beneficial effect has been ascribed to the phenol compounds, the squalene and the oleic acid that it contains. The European Union is the leading world producer of olive oil, with roughly 80% of the total output (over 2 million tons per year). Spain alone accounts for 34% of the global production figure. 3 Spanish olive groves are located mainly in Andalusia, a strongly agriculture- dependent region where the competent council is continu- ously striving to preserve the high-quality features of olive oil, and to maintain strict control of its quality. The high price of high-quality olive oil often elicits adulteration with other, cheaper seed oils (e.g. corn oil) or mixing with olive oils of lower quality. Moreover, the emergence of oils with protected designations of origin (PDO) has raised the need to check that oils actually come from the stated production area. New, validated methods are therefore required to assure the authenticity and traceability of PDO olive oils in order to protect consumers and producers from any illicit practices. d 13 C and d 18 O isotope ratio measurements have been used for traceability purposes in foods including wine, honey and juices, 4–14 but rarely in olive oil. The few reported uses for the latter purpose involved identifying fraud in the form of mixing with other vegetable oils or lower-quality olive oils. One other potential use of isotope ratio measurements in this context (viz. identifying the geographical origin of olive oils) remains largely unexplored, however. d 13 C values have been used to distinguish fats from plants following C 3 and C 4 fixation pathways. 15 Oils from the C 3 cycle have been discriminated by isotope measurements of whole oil and some oil fractions. Thus, Kelly et al. 16 examined the d 13 C values for various fatty acids including palmitic, stearic, oleic and linoleic in different single-seed vegetable oils following the C 3 photosynthetic pathway and concluded that such values by themselves did not allow fraud to be ascertained, but provided valuable complementary infor- mation to that from other analytical techniques. Angerosa et al. 17 used d 13 C measurements for the aliphatic alcohol fraction to detect adulteration of olive oil with as little as 5% of cheaper pomace oil. Woodbury et al. 18 found that the d 13 C values for various vegetable oils were very similar to those of their individual fatty acids, which differed only slightly from one another. Furthermore, although esterifica- tion at position 2 in the glycerol follows a different enzymatic pathway from that at positions 1 or 3, fatty acids from any position on the glycerol backbone are isotopically identical. Bianchi et al. 19 measured d 13 C in olive oils and in their sterol, glycerol and long-chain alcohol fractions, and drew three interesting conclusions, namely: (a) the d 13 C values for the three fractions were consistent with a C 3 biosynthetic pathway; (b) the values for the oils differed significantly from those for their respective fractions; and (c) the degree of ripeness of the olives had no influence on the d 13 C for the oils. RAPID COMMUNICATIONS IN MASS SPECTROMETRY Rapid Commun. Mass Spectrom. 2007; 21: 487–496 Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/rcm.2862 *Correspondence to: A. Marinas, Department of Organic Chem- istry, University of Co ´ rdoba, Campus de Rabanales, Marie Curie Building, E-14014 Co ´ rdoba, Spain. E-mail: alberto.marinas@uco.es Contract/grant sponsor: Consejerı ´a de Innovacio ´n, Ciencia y Empresa; contract/grant number: FQM 191. Contract/grant sponsor: Consejerı ´a de Agricultura y Pesca de la Junta de Andalucı ´a and Spanish Ministerio de Educacio ´n y Ciencia; contract/grant number: CTQ2005-04080/BQU, cofunded by FEDER. Copyright # 2007 John Wiley & Sons, Ltd.