ABSTRACT
Starch is a major energy store in many plants and microorganisms. Semi-crystalline starch granules consist of two major glucans known as amylose and amylopectin. Amylose is a linear or slightly branched polymer with a comparatively simple structure that forms helical inclusion complexes with a range of ligands, such as fatty acids and iodine. Amylopectin, which is the major polymer in most starch granules, is extensively branched. It is considerably larger and has a more complex structure than amylose. In addition, some starch granules, notably those from mutant plants, contain materials with structures intermediate between amylose and amylopectin. The cluster model, originally proposed in the early 1970s, suggests that short chains of amylopectin are clustered and form double helices that constitute crystalline lamellae in the starch granules. However, more recent structural analyses of isolated -dextrins have challenged the accuracy of this traditional model. Instead, the so-called building block backbone model offers a rational platform that not only explains the semi-crystalline structure of the starch granules, but also systematically organizes the starches based on four distinct structural types of amylopectin
