Starch granules layered structure

Figure 20-3 Proposed structure of a molecule of amylopec-tin in a starch granule. The highly branched molecule lies within 9 nm thick layers, about 2 / 3 of which contains parallel double helices of the kind shown in Fig. 4-8 in a semicrystalline array. The branches are concentrated in the amorphous region.113 114 121 Some starch granules contain no amylose, hut it may constitute up to 30% by weight of the starch. It may he found in part in the amorphous bands and in part intertwined with the amylopectin.122...

Starch changes during cooking of pasta are reported to vary from a hydration-driven gelatinization process in the outer layer to a heat-induced crystallite melting in the center.525 It is speculated that both the state of the starch and the surface structure contribute to the development of the elastic texture and stickiness of pasta. Interactions between starch and the surrounding protein matrix are evident in the outer and intermediate layer. In the center of cooked pasta, wheat starch granules retain their shape due to limited water diffusion, and the protein network remains dense. 

Construction of the starch granule. It is unlikely that the several fractions are haphazardly thrown together to form the granule. Three types of granule structure have been proposed (1) Location of one fraction as a surface hull-substanz, (2) alternate onion-like layers of the fractions, and (3) arrangement in radial or trichitic fashion. The orientation of the individual molecules must also be considered. 

Starch granules show a characteristic pattern of growth rings of 0.3- to 0.4-pm thickness with thinner dense layers about 7 run apart. Study of this layered structure suggests that the individual amylopectin molecules have branches close together in broomlike clusters (Fig. The amylopectin chains are... 

It was also noticed that these pores penetrated into the inner layers of the granules during enzymic action and in some granules, a terraced or step-shaped appearance in their inner portions was observed. These internal characteristics are probably indicative of a layered internal structure in the granules. The other observations from scanning electron microscopy were the presence of striated structures on the surface of starch granules from banana, lily, and lotus which had been attacked by pancreatin. 

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