Internal structure of the starch granule revealed by AFM

Atomic force microscopy images of sectioned native corn starch granules show evidence of the well-known radial organisation of the starch macromolecules, with the less-ordered hilum region near to the centre. Native granules show blocks 400-500 nm in size that span the growth rings. Lintnerised starch granules, where a mild acid hydrolysis has been used to remove the amorphous and less crystalline parts of the granule, clearly show smaller 'blocklets' within the rings approximately 10-30 nm in size. This level of organisation within the growth rings corresponds to the blocklet or superhelix structures that have been proposed in the literature for the association or clustering of amylopectin helices. Mechanical property imaging techniques have provided enhanced contrast to view this morphology, and shown the deformability of the starch structure under contact mode imaging conditions.