Using AFM to image the internal structure of starch granules

Abstract

Atomic force microscopy (AFM) has been used to observe the ultra-structure of starch granules for starches from different botanical sources (maize and potato). Starch granules were embedded, sectioned and imaged in dc constant force topographic, error signal and force modulation modes. AFM images of the starches embedded in Nanoplast ®, a resin previously used for AFM and electron microscopy studies, failed to reveal the growth ring structure within the granules consistently. Furthermore, ultra-structural features could not unequivocally be attributed to the ‘blocklet’ structure of the granule because of the underlying granular texture of the resin itself. In contrast the use of rapid setting Araldite, a non-penetrating resin, allowed the ultra-structure of the granules to be viewed without the necessity of pre-treatment (lintnerisation or enzymatic degradation) steps. The images demonstrated clearly the importance of the choice of embedding material, and showed that under the correct conditions ‘growth rings’ and blocklet structures can be observed in ‘near native’ granules.