Structural characterization and thermal properties of amylose-fatty acid complexes prepared at different temperatures

Amylose-fatty acid complexes were prepared in aqueous alkaline solution at 30, 50 or 70 °C. The complexes were obtained as precipitates from solution after neutralization. XRD diffractograms showed that all complexes were semicrystalline regardless the temperature of their preparation whereas they revealed the presence of two extra peaks at 2θ = 21.7° and 23.8° apart from those attributed to V-type structure of complexed amylose. These peaks were attributed to free fatty acid molecules entrapped inside the matrix of the complexes. DSC thermograms showed that the values of endothermic peaks attributed to dissociation of the complexes ranged from 90 to 120 °C. The dissociation temperature of the complexes increased with increase in the preparation temperature and the fatty acid chain length. For the removal of free fatty acid molecules present in the matrix of the complex, the samples were treated with different solvents which managed to remove only part of the free fatty acid.