Submitted to: Carbohydrate Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 2005
Publication Date: January 20, 2006
Citation: Shogren, R.L., Fanta, G.F., Felker, F.C. 2006. X-ray diffraction study of crystal transformations in spherulitic amylose/lipid complexes from jet-cooked starch. Carbohydrate Polymers. 64(3):444-451. Interpretive Summary: Corn starch and fatty acids readily form helical complexes in which the starch chain wraps around the fatty acid molecule. Although these complexes have been studied in the past, there are many details of their structure and stability which remain poorly understood. Such knowledge is necessary to better understand starch-fat interactions in food, effects on starch digestion and the development of non-food uses for starch. It was found that drying and rewetting causes an irreversible contraction in the diameter of the starch-lipid helix. It was also found that the lipid component of these crystals can be largely removed by extraction with alcohols, leaving the structure of the hollow starch helix intact. Such hollow "nanotubes" could have new uses as selective absorbents and catalysts. This information should be useful to other academic and government researchers and to gain processing companies developing new uses for starch.
Technical Abstract: The effects of drying, solvent extraction and rehydration on the structures of V-type amylose/lipid complexes from slowly cooled jet-cooked corn starch 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 (7 -1 helices in orthorhombic unit cell). After freeze-drying, the X-ray pattern changed to a more disordered hexagonal array of 7 -1 helices. Rehydration in water caused a change to the 6 -1 orthorhomibic structure and then to the 6 -1 hexagonal structure after a second freeze drying. Extraction of the freeze-dried 7 -1 form 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 V -6 form. The diffraction patterns of small particle amylose-lipid complexes (V -6) were unaffected by either rehydration with water or extraction with alcohol or alcohol/water mixtures. Small angle X-ray scattering curves show small peaks at d=70-80 Angstroms, suggesting the presence of chain-folded crystallites.