Using offline HPLC-GC-FID 4-Desmethylsterols Concentration Profiles, Combined with Chemometric Tools, to Discriminate Di
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Using offline HPLC-GC-FID 4-Desmethylsterols Concentration Profiles, Combined with Chemometric Tools, to Discriminate Different Vegetable Oils D. Gázquez-Evangelista & E. Pérez-Castaño & M. Sánchez-Viñas & M. G. Bagur-González
Received: 27 July 2013 / Accepted: 22 November 2013 / Published online: 21 December 2013 # Springer Science+Business Media New York 2013
Abstract In order to improve the separation of the sterol classes present in vegetable oils, an isocratic off-line HPLC fractionation of unsaponifiable has been developed using a cyano-bonded phase column as stationary phase and hexane/tert-butylmethyl ether (80:20 (v /v )) as mobile phase, which permits to obtain them in less than 12 min. With the aim of evaluating the developed procedure, different samples of edible oils, such as extra virgin and pomace olive oil, sunflower, soybean, etc., were analyzed by GC-FID. The concentration of each phytosterol was found by means of an internal calibration at one level, using α-cholestanol as surrogate and theoretical correction factors. Their concentration profiles have been used to provide a pattern capable of distinguish among different vegetable oils. The chemometric study based on the Hierarchical Cluster Analysis and Factor Analysis (FA) using principal components and Varimax rotation was applied to the Box-Cox transformed data set to obtain the natural classes used in the final Linear Discriminant Analysis. Two discriminant functions explaining the 94.89 % of the total variance has been considered enough to classify the studied samples.
Keywords Vegetable Oils . HPLC sterols fractionation . Theoretical correction factors (TCF) . Phytosterols determination . Box-Cox transformation . Pattern recognition methods
D. Gázquez-Evangelista : E. Pérez-Castaño : M. Sánchez-Viñas : M. G. Bagur-González (*) Department of Analytical Chemistry, Faculty of Sciences, University of Granada, Avda. Fuentenueva s/n, 18071 Granada, Spain e-mail: [email protected]
Introduction The interest in phytosterol determination in foods, oils, and diets is growing not only for their beneficial effects for health but also because they can be used to detect olive oil in the presence of other vegetable oils. On one hand, the official analytical procedure for the analysis of phytosterols in olive oil involves several steps (International Olive Oil Council Technical Documents, 2009; Commission Regulation (EC) No 2568). First, the oil is saponified to remove triglycerides and the unsaponifiable compounds are extracted with an organic solvent; then, the unsaponifiable matter is fractionated into several classes of compounds by thin layer chromatography (TLC), and the phytosterols are collected and analyzed by gas chromatography–flame ionization detection (GC-FID), as trimethylsilyl derivatives. As it is well known, the TLC step to isolate the phytosterols fraction is time consuming and tedious; so, other alternatives have been developed to achieve this objective: (1) solid phase extraction, in normal or reverse phase mode (Phillips et al. 2002; To
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