Amylopectin is a highly branched polymer and contains mostly α-D-1,4- anhydroglucose linkages along with α-D-1,6-anhydroglucose linkages at the branch points. The molecular weight of amylopectin is 106-108 Da (Whistler et al. 1984). Each branch contains 20 to 30 anhydroglucose units and the degree of polymerization is about 2 million units. The large size and branched nature of the amylopectin polymer reduces its mobility and prevents the polymers from becoming oriented close enough to permit hydrogen bonding. As a result, aqueous solutions of amylopectin are clear and resistant to gelling upon ageing.
Amylopectin is usually assumed to support the framework of the crystalline regions in the starch granule. It has been shown that branching points do not induce extensive defects in the double helical structure (Imberty and Perez 1988; Buléon and Tran 1990).
The molecular structure of amylopectin is described by the cluster model first proposed by French (1972) and Robin et al. (1974). The cluster model generally accepted today (Hizakur 1986).
The crystalline and non-crystalline structures are major factors influencing the properties of the starch granules (Zobel 1988). The crystalline shells consist of alternating amorphous and crystalline lamellae which are approximately 9-10 nm thick (Jenkins and Donald 1995; Gallant et al., 1997).
There are three different types of crystalline structure (A, B, and C) for amylopectin within the crystalline lamellae. A-chains are associated with one cluster while B-chains are involved in one, two, or three clusters. A-chains are those that are linked to the rest of the molecule only through their reducing ends. B-chains are linked to the molecule through their reducing ends but, in addition, are branched at a C-6 position in one or more of their Dglucopyranosyl residues (Jenkins and Donald 1995). C-chains are those that bear the reducing end group. Potato starch has a B-crystalline pattern (Young 1984).