Analysis of the native structure of starch granules with small angle X-ray microfocus scattering
1999
Waigh, T.A. | Donald, A.M. | Heidelbach, F. | Riekel, C. | Gidley, M.J.
Small angle x-ray microfocus scattering patterns were obtained from 4 micrometer regions of hydrated potato starch granules. The 9 nm lamellar reflection was found to be modulated along two flat streaked layer lines symmetrically related, and arranged in a weak four point pattern. This provides evidence for two populations of tilted lamellae in the granule present in equal quantities, but opposite angles of tilt. The paucity of reflections in the scattering patterns implies the existence of correlated disorder between the lamellae, and is a product of either their liquid crystallinity or a well-developed defect structure between the constituent amylopectin helices. The angular position of the four point modulation (17.25 degrees) on the scattering patterns is compared with the values predicted from a superhelical lamellar model containing cumulative disorder along its axis, and good agreement is found with the data. The physical basis for the occurrence of these helical lamellae is examined on the basis of the model of amylopectin as a chiral side chain liquid-crystalline polymer (T. A. Waigh et al., Macromolecules, 1997, Vol. 30, pp. 3813-3820; Faraday Discussions, 1996, Vol. 103, pp. 325-337).
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