X-ray diffraction study of crystal transformations in spherulitic amylose/lipid complexes from jet-cooked starch

The effects of drying, solvent extraction and re-hydration on the structures of V-type amylose/lipid complexes from slowly cooled jet-cooked cornstarch dispersions were investigated using X-ray powder diffraction. Large spherulites in the wet state or dried in humid air had X-ray patterns similar to those found previously for wet amylose–isopropanol complexes (71 helices in orthorhombic unit cell). After freeze-drying, the X-ray pattern changed to a more disordered hexagonal array of 71 helices. Surprisingly, re-hydration in water caused a change to the 61 orthorhombic structure and then to the 61 hexagonal structure after a second freeze-drying. Extraction of the freeze-dried 71 forms with boiling anhydrous propanol did not change the diffraction pattern significantly but resulted in extraction of half of the complexed lipids. Extraction with boiling n-propanol/water resulted in complete lipid extraction along with conversion to the hexagonal V6 form. The diffraction patterns of small particle amylose–lipid complexes (V6) were unaffected by either re-hydration with water or extraction with alcohol or alcohol/water mixtures. Small angle X-ray scattering curves show small peaks at d=70–80 Å, suggesting the presence of chain-folded crystallites.