Fatty acid composition and rheological behaviour of prickly pear seed oils

Prickly pear fruits constituted valuable foodstuff for humans and animals in arid and semi-arid regions. Two species of prickly pear from Tunisia, Opuntia ficus indica and Opuntia stricta, were investigated for fatty acid composition and physicochemical parameters of the seed oil. No significant difference in either physical or chemical parameters was found between the species. The main fatty acids of prickly pear seed oil were C16:0, C18:0, C18:1, C18:2. With an exceptional level of linoleic acid, up to 70%, the content of unsaturated fatty acids was high, at 88.5% and 88.0% for O. ficus indica and O. stricta, respectively. Rheological properties were analysed with changes of temperature and shear stress. Variations of viscosity were measured and the viscoelastic parameters were determined during heating and cooling cycles between 20 and 70 C. Curves of flow were established with up and down cycles of shear stress at different temperatures. These measures highlighted the presence of large aggregates of crystal fatty acids in both Opuntia crude oils. Shearing and temperature destroyed this structural state and gave birth to an homogeneous stable suspension. The structural state of crude oil was confirmed using a contrast phase microscope, and the particle size distribution was obtained by laser granulometry. 2004 Elsevier Ltd. All rights reserved.