DSC analysis: a potential tool for detection of extravirgin olive oil adulteration

Adulteration of extravirgin olive oil with seed oils has always represented a problem for the Mediterranean countries that produce and import this type of product. The determinations of fatty acids by gas chromatography (GC) and triacylglycerols by high-performance liquid chromatography (HPLC) are considered well-established methods for authenticity and quality control of olive oil [1, 2]. Differential Scanning Calorimetry (DSC) has been recently suggested as a valuable tool for characterization of oils from olive and other vegetable sources; the DSC parameters have been reported to well correlate with chemical parameters obtained with standard methods [3, 4]. DSC has already been applied to detect adulterated butter with beef body fat and margarine, to determine the presence of animal fat in canola oil and in palm olein, and to investigate the presence of foreign fat in chocolate [5-8]. The aim of this work was to evaluate the potential use of DSC to detect adulteration of extravergin olive oil. Extravirgin olive oil was mixed with canola oil or sunflower oil in different percentages (60:40, 70:30, 80:20 and 95:5, w/w). Thermograms were obtained by means of DSC (TA Instruments, New Castle, DE) cooling from 30 to -80°C at 2°C/min, isothermal for 3 min and heating from -80 to 30°C at 2°C/min. The crystallization and melting profiles were obtained for of each oil and their mixtures and overlapping transitions of thermograms were deconvoluted into the individual constituent peaks using PeakFitTM software (Jandel Scientific, CA). Addition of canola and sunflower oil significantly shifted the crystallization temperature exothermal peak of extravirgin olive oil to lower temperatures. However, the enthalpy of crystallization of extravirgin olive oil was not significantly modified by canola oil addition, but it was significantly lowered by sunflower oil, probably due to the higher linoleic acid content of the latter. The crystallization exothermic peak was deconvoluted into three distinct components, which may correspond to the three major triacylglycerol groups (monosaturated, disaturated and triunsaturated) present in the oils and their mixtures. Addition ofseed oils influenced area percentages of the deconvoluted peak, according to compositional data of the oils. In particular, the admixtures withcanola oil led to an increase of the peak area corresponding to both major saturated and unsaturated fractions. However, the addition of sunflower oil increased the peak area of the intermediate fractions. The melting of the crystallized admixture exhibited complex lineshapes influenced by the presence of seed oils, especially at higher concentration (30-40%), reducing the area of the high-melting peak group. The addition of canola oil lowered Ton of melting curves and increased the transition range, whereas the addition of sunflower oil lowered Ton, Toff and the enthalpy of the melting curves. References 1-Christopoulou, E, Lazaraki, M, Komaitis, M, Kaselimis, K Food Chem, 2004, 84, 463-474. 2-Andrikopoulos, NK, Giannakis, IG, Tzamtzis,V J Chromat Sci, 2001, 39, 137-145. 3-Tan, CP, Man, YB, Lipid Technol, 2002, 9, 112-115. 4-Tan, CP, Man, YB, Phytochem Anal, 2002, 13, 129-141. 5-Coni, E, Pasquale, M, Coppolelli, P, Bocca, A, J AOAC Int, 1994, 71, 807-810. 6-Marikkar, JMN, Ghazali, HM, Che Man,YB, Lai, OM., J Food Lipids, 2003, 10, 63-79. 7-Marikkar, JMN, Ghazali,HM, Che Man,YB, Lai, OM, Food Res Intern, 2002, 35, 1007-1014. 8-Lipp, M, Anklam, E, Food Chem, 1998, 62, 99-108.