DSC analysis of monovarietal extra virgin olive oils: correlation between thermal properties and chemical composition

Extra virgin olive oil is widely produced and consumed in the Mediterranean area. The quality and uniqueness of extra virgin olive oil is primarily determined by genetic and climatic factors, as well as by the physiological condition of the olives which influences the biomolecular components of the finished product (i.e. the triacylglycerols and the biophenolic minor components). Differential Scanning Calorimetry (DSC) has been recently proposed as a valuable tool for characterization of oils from olive and other vegetable sources. DSC parameters have been reported to well correlate with the parameters obtained with standard chemical methods. The aim of this work was to evaluate thermal properties of extra virgin olive oils from different cultivars and ripening degree to establish a correlation with their chemical composition. Thermal profiles of monovarietal extra virgin olive oils (Cerasuola, Nocellara del Belice and Biancolilla cultivars) from Sicily at three different ripening degrees were evaluated by means of DSC (TA Instruments, New Castle, DE). Thermograms were obtained (30/-80°C range, 2°C/min) to characterize the crystallization and melting profile of each oil. Overlapping transitions were deconvoluted into individual constituent peaks using a PeakFitTM software (Jandel Scientific, CA). Chemical composition of oil samples was evaluated by means of triacylglycerol, diacylglycerol and total fatty acids composition. The crystallization curves showed one exothermic peak that was deconvoluted into three distinct components. Total crystallization enthalpy did not differ among the oils studied while differences were observed in the enthalpy of cristallization of the deconvoluted peaks in the Biancolilla and Cerasuola cultivars. Similar differences were also found in oils obtained from more ripened olives. The deconvoluted peaks may correspond to the three major triacylglycerol groups (mono-, di- and three unsaturated) present in the oils. The melting of the crystallized and frozen oils exhibited more complex lineshapes consisting of six overlapping peaks and probably ascribable to different polymorphic forms. Differences in DSC thermal behaviour correlated to the differences in chemical composition among cultivars and ripening degree of the olives. composition among cultivars and ripening degree of the olives.