Starch cluster model

Maltese cross (Blanshard, 1979). The crystallinity of starch is caused essentially by amylopectin pol)Tner interactions (Banks and Greenwood, 1975 Biliaderis, 1998 Donald, 2004 Hizukuri, 1996). An illustration of currently accepted starch granule structure is given in Fig. 5.5. It is believed that the outer branches of amylopectin molecules interact to arrange themselves into "crystallites" forming crystalline lamellae within the granule (Fig. 5.5 Tester et al., 2004). A small number of amylose polymers may also interact with amylopectin crystallites. This hypothetical structure has been derived based on the cluster model of amylopectin (Hizukuri, 1986 Robin et ah, 1974 Fig. 5.1). 

Amylopectin molecules are large flattened disks consisting of (1 —4)-linked a-glucan chains joined by frequent 6)-branch points. Many models of amylopectin structure have been proposed. The most satisfactory models are those proposed by Robin et al.,18 Manners and Matheson,19 and Hizukuri 20 all are known as cluster models. Reviews by Morrison and Karkalis21 and Hizukuri22 discuss in detail the chemical and physical aspects of the starch granule and its components, amylose and amylopectin. 

Figure 5.11 Representation ofthe double helix of crystalline starch after modeling a branching point between two strands. Schematic cluster model of amylopectin molecule incorporating the double helical fragments. (Reproduced with permission from reference 45)...

The accepted models of proposed amylopectin stmctures, which are known as cluster models, are those of Robin et al. (8), Manners and Matheson (9), and Hizukuri (10). Reviews that detail chemical and physical properties of starch are given by Morrison and Karkalis (11) and Hizukuri (12). Figure 1 shows the proposed cluster structure. 

Debranching studies of starch lends further support to the idea that a blocklet level of structure exists. Hizukuri15 demonstrated that B-chains of amylopectin can participate in more than one crystalline amylopectin side chain cluster, and proposed a revised model of amylopectin structure, classifying the B-chains according to the number of side chain clusters in which they participate. From this work, it is evident... 

Figure 9.1 A model of starch granule structure (a) single granule, (b) expanded view of internal structure and (c) the cluster structure of amylopectin. Amylopectin is a branched polymer, seen here extending through many crystalline and amorphous lamellae. (Taken from [3] - Reproduced by permission of The Royal Society of Chemistry.)...

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