Microscopy of starch: evidence of a new level of granule organization

Considerable information on starch granule structure may be gathered from a review of published data. Evidence from a range of different (predominantly microscopic) techniques is compared and discussed, allowing the presence of a level of starch granule organization between that of the amylopectin lamellae and the large ‘growth rings’ to be deduced. This structural level of the granule involves the organization of the amylopectin lamellae into effectively spherical ‘blocklets’ which range in diameter from 20 to 500 nm depending on starch botanical type and their location in the granule. The presence of short, radial ‘channels’ of amorphous material within starch granules from some starch varieties is confirmed. The organization and structure of the crystalline and amorphous amylopectin lamellae is also discussed. Consideration of the information regarding starch granule structure and organization to date has significant implications on the internal architecture of the starch granule, and it is evident that the presence of the blockets and amorphous channels play a role in both the resistance of starch to enzymic attack and the structure of the semi-crystalline shells.