Classification of vegetable oils according to their botanical origin using amino acid profiles established by direct infusion mass spectrometry Marı ´a J. Lerma-Garcı ´a * , Guillermo Ramis-Ramos, Jose ´ M. Herrero-Martı ´nez and Ernesto F. Simo ´ -Alfonso Department of Analytical Chemistry, Faculty of Chemistry, University of Valencia, 46100 Burjassot, Valencia, Spain Received 23 July 2007; Revised 14 September 2007; Accepted 14 September 2007 Amino acid profiles, established by direct infusion mass spectrometry, have been used to classify vegetable oils according to their botanical origin. The proteins present in hazelnut, sunflower, corn, soybean, olive, avocado, peanut and grapeseed oils were precipitated with acetone, and the residue was hydrolyzed in acid medium, diluted in a hydrochloric acid/ethanol mixture, and infused into the mass spectrometer. The spectra of the hydrolyzed protein extracts showed [MRH] R ions of the following amino acids: glycine, alanine, serine, proline, valine, threonine, cysteine, isoleucine R leu- cine, aspartic acid, lysine, glutamic acid, methionine, histidine, phenylalanine, arginine and tyrosine. These ions were used to construct linear discriminant analysis (LDA) models. The ratios of the ion signal intensities selected by pairs were used as predictors. With the sequential application of three LDA models, the eight botanical origin categories of the samples were well resolved. Copyright # 2007 John Wiley & Sons, Ltd. Oil authenticity is a very important aspect of quality edible oils. Extra virgin olive oil, due to its high price, is occasionally adulterated with olive oils of lower quality, or with oils of a different botanical origin. 1–6 To establish the authenticity of edible oils a number of chromatographic methods 1,2,6–8 and spectroscopic techniques including fluorescence, 4,9 FTNIR, 10 FTIR, 5,10 FT-Raman, 10 NMR, 11–15 and MS, 1,3,16 followed by multivariate statistical analysis of the data, have been applied. For this purpose, the contents of fatty acids, 8 tocopherols, 9 volatile compounds, 1 and sterols 6 have been used. The presence of different enzyme activities, which implies the presence of proteins, has been demonstrated in olive oils; 17,18 however, only in few reports have proteins been recognized as components of olive oils. 19–21 The influence of proteins in olive oil stability has been studied. Proteins react with lipid oxidation products, yielding endogenous anti- oxidants in food systems. 22–24 However, due to their low concentrations, proteins do not seem to play a clear role in oil stability. 25 Polypeptides similar to those found in olive oils have been detected in other vegetable oils, 19 which opens the way to use polypeptides and amino acids to classify the oils according to their botanical origin. Amino acid profiles obtained by protein hydrolysis have been used to classify different categories of samples in art works 26–29 and rice cultivars. 30 The contents of free amino acids have also been used to classify tea samples, 31 to establish the quality of beer, 32 and to characterize fortified wines. 33 Hidalgo et al. 19,20 have developed a method to determine peptides and proteins in fats and oils by precipitation and hydrolysis, followed by amino acid analysis by high- performance liquid chromatography (HPLC) with ultra- violet (UV) detection. Reported protein contents in edible oils vary widely, depending on the type and source of the oil, as well as on the methodology used for extraction and analysis. 25 The total protein content and the amino acid composition in olive fruits of the Arbequina and Picual varieties at three stages of ripening have been studied; significant differences according to either the cultivar or the fruit ripening stage were not found. 21 In this work, the amino acid profiles of oils of eight different botanical origins, as well as olive oils of different genetic varieties, have been obtained by direct infusion mass spectrometry. The spectral data were used to construct linear discriminant analysis (LDA) models. With the sequential application of three LDA models, the oil samples were well classified with an excellent resolution according to their category of origin. RAPID COMMUNICATIONS IN MASS SPECTROMETRY Rapid Commun. Mass Spectrom. 2007; 21: 3751–3755 Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/rcm.3272 *Correspondence to: M. J. Lerma-Garcı ´a, Department of Analytical Chemistry, Faculty of Chemistry, University of Valencia, 46100, Burjassot, Valencia, Spain. E-mail: mlergar@alumni.uv.es Contract/grant sponsor: MEC and FEDER; contract/grant num- ber: CTQ2004-06302. Contract/grant sponsor: Generalitat Valenciana; contract/grant number: ACOMP07-168. Copyright # 2007 John Wiley & Sons, Ltd.