Authentication of Olive Oil: Detection of Adulteration with Hazelnut Oil by Direct Coupling of Headspace and Mass Spectrometry

Due to its higher price, compared to other edible oils, control of adulteration of the olive oil is one of the main aspects to be evaluated in its quality control. Adulteration with hazelnut oil is one of the most difficult to be detected due to the great similarity existing in the composition of hazelnut and olive oils; both virgin olive oil and olive oil are subjected to that kind of adulteration. The main objective of this work was to develop an analytical method able to detect adulteration of virgin olive oils and olive oils with hazelnut oil by means of its analysis by a headspace autosampler directly coupled to a mass spectrometer used as detector. No chromatographic separation of the individual components of the samples exists, so, a broad single signal of the sample is obtained and employed for its characterization as a chemical fingerprint. Multivariate regression techniques (Partial Least Squares and Principal Components Analysis) were applied in this context to generate adequate regression models. Good values were obtained in both techniques for the parameters employed (SEP and PRESS) to evaluate its goodness. Once validated, the method was applied to the detection of such adulteration in commercial olive oil and virgin olive oil samples. INTRODUCTION Despite its high price, olive oil is highly appreciated by consumers due to its pleasant flavour and nutritional benefits, Thus, its adulteration with other cheaper oils can lead to large economical profits. In this way, authentication of virgin olive oils has become an interesting subject from both commercial and health perspectives [1]. Nowadays, one of the most concerning adulterations found in virgin olive oil (VOO) is carried out with hazelnut oil (Corylus Avellana L.), on account of their similar composition as regards triacylglycerol, total sterol and fatty acid profile, rich in monoand polyunsaturated fatty acids, specially oleic and linoleic [2,3]. EU authorities have expressed concern about quality control of olive oil, specially its adulteration with hazelnut oil [4]. Filbertone [(E)-5-methylhept-2-en-4-one] has been identified as responsible for the flavour of hazelnut oil [5]. Its absence in VOO makes it ideal as a marker of adulteration. Analytical methods described for the detection of filbertone in VOO, include multimodal LC-GC separation [6], stable isotope dilution [7] and GC coupled to different sample preparation techniques [8,9]. Authentication and characterization of hazelnut oil, and its use as adulterant in VOO, has been reported by using NMR [10], mid-IR [11] and RAMAN [12] spectroscopies and multivariate statistical techniques. Recently, the direct combination of headspace sampling and mass spectrometry (HS-MS) has been proposed as a competitive fast-response analytical tool for the characterization of edible oil samples, especially olive oil [13]. That system enables to obtain a chemical « fingerprint » of the sample by the direct analysis of the whole volatile fraction, what can be used for its authentication and to control its purity. Several applications of the system can be found in the literature concerning the use of HS-MS for olive oil authentication. Marcos-Lorenzo et al. [14] employed this system to develop a methodology to detect adulteration with suflower and olive-pomace olive oil, by means of linear discriminant analysis as chemometric approach for data treatment. Our research group has also proposed some methods to control VOO quality focused on classification of the three main types of olive oil (virgin olive oil, olive oil and olive-pomace olive oil) by using several pattern-recognition techniques [15], determination of hexane residues in olive-pomace olive oil with two multivariate regression techniques [16] and screening of volatile benzene-hydrocarbon residues in VOO [17].