HIGH-RESOLUTION IMAGING OF STARCH GRANULE SURFACES BY ATOMIC-FORCE MICROSCOPY

High resolution imaging of the surfaces of starch granules from two di fferent botanical sources has been performed using two complementary t echniques: low voltage scanning electron microscopy (LVSEM) and atomic force microscopy (AFM). LVSEM provided superior images of uncoated gr anules than possible by conventional scanning electron microscopy, and these images were used to validate the features revealed at higher re solution by AFM. The AFM images demonstrated that, although intra-samp le variation exists, the surfaces of wheat and potato starch granules possess substantially different topographies. Potato starch had many p rotrusions (50-300 nm in diameter), above a Batter surface, which cont ained structures in the order of 10-50 nm. Wheat starch had far fewer protrusions and generally had a smoother surface made up of 10-50 nm s tructures. The 10 to 300 nm structures are believed to be carbohydrate in nature and correspond to (blocklet' structures, comprising groups of amylopectin side-chain clusters presenting at the granule surface. We conclude therefore that near-molecular resolution topography of the starch granule surface has been revealed, which has allowed further i nsight into starch granule structure and molecular organisation. (C) 1 998 Academic Press Limited.