The double helices within the A- and B-type polymorphic forms are essentially identical with respect to helical structure (Gidley, 1987; Imberty et al., 1991). However, the packing of these double helices within the A-type polymorphic (crystalline) structure is relatively compact with low proportion of structural water, whilst in B-type crystallites the double helices are less densely packed creating a more open structure and contain a hydrated helical core (Fig. 1.5). The factor that most likely influences the pattern in plants is the length of the amylopectin chains, which are shorter in A-type starches. Both amylose and amylopectin can form crystalline structures. It is assumed that branching points of amylopectin favor helix formation. However, crystalline structures present in native starch
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