Internal structure of the starch granule revealed by AFM

Atomic force microscopy images of sectioned native corn starch granules sho w evidence of the well-known radial organisation of the starch macromolecul es, with the less-ordered hilum region near to the centre. Native granules show blocks 400-500 nm ill size that span the growth rings. Lintnerised sta rch granules, where a mild acid hydrolysis has been used to remove the amor phous and less crystalline parts of the granule, clearly show smaller 'bloc klets' within the rings approximately 10-30 nm in size. This level of organ isation within the growth rings corresponds to the blocklet or superhelix s tructures that have been proposed in the literature for the association or clustering of amylopectin helices. Mechanical property imaging techniques h ave provided enhanced contrast to view this morphology, and shown the defor mability of the starch structure under contact mode imaging conditions. (C) 2001 Elsevier Science Ltd. All rights reserved.