Crystallization and melting properties of extra virgin olive oil studied by synchrotron XRD and DSC

Crystallization and melting properties of triacylglycerols in extra virgin olive oil were studied by using synchrotron X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The phase transitions were monitored by cooling and heating the samples at 2 degrees C/min from 60 to 60 degrees C and vice versa. Upon cooling, a first DSC endothermic peak was recorded at 9.6 degrees C followed by one at 33.5 degrees C. These thermal events were associated to the formation of two different structures: a triple-chain length (3L) having a c parameter of about 58.38 angstrom and a quadruple chain length structure (4L) with a c parameter of about 89.99 angstrom, respectively. Both structures evidenced a cell packing arrangement ascribable to a form. During heating, part of the metastable crystals rearranged into the more thermodynamically stable form. Then, upon further heating, the sequential melting of the two crystal structures was observed. The melting was completed at 10.7 degrees C. Beside this interpretation of XRD data, a model considering a cell with a c parameter of about 170 angstrom and a hexagonal crystal system was proposed. Even if more research is needed to validate this approach, it allowed all XRD events recorded during the experiments to be described.