Amylose crystalline

OH stretching V-amylose (crystalline) B-amylose (crystalline) Amorphous... 

With some of these polymers, a real complexation of single helical amylose with the polymer backbone can happen, which gives rise to supramolecular stmctures characterized by V-type crystallinity. This sort of modified amylose crystallinity is the same mentioned in section 2.4.4 and has been widely studied with small molecules such as alcohols, glycerol, dimethylsulphoxide, fatty acids, or iodine [66]. 

Chaudhary DS (2008) Understanding amylose crystallinity in starch-clay nanocomposites. 

Immediately after the processing (e.g., extrusion cooking) the starch does not show any residual crystaUinity (or values lower than one percent). However, some hours after the manufacture a new type of crystallinity will develop. The structures are formed by single helices of amylose and they can be divided into three types, called the V type (non-hydrated), the Vh type (hydrated), and the Eh type. The Eh structure is not stable and under the influence of moisture it changes during storage into the Vh type, although the total amount of amylose crystallinity remains the same [20-22, 30, 34]. 

Starch is made thermoplastic at elevated temperatures ia the presence of water as a plasticizer, aHowiag melt processiag alone or ia blends with other thermoplastics (192—194). Good solvents such as water lower the melt-transition temperature of amylose, the crystalline component of starch, so that processiag can be done well below the decomposition—degradation temperature. 

Polycrystalline and well-oriented specimens of pure amylose have been trapped both in the A- and B-forms of starch, and their diffraction patterns84-85 are suitable for detailed structure analysis. Further, amylose can be regenerated in the presence of solvents or complexed with such molecules as alcohols, fatty acids, and iodine the molecular structures and crystalline arrangements in these materials are classified under V-amylose. When amylose complexes with alkali or such salts as KBr, the resulting structures86 are surprisingly far from those of V-amyloses. 

From measurements of the dichroism of flow of amylose-iodine solutions,161 and from studies of the optical properties of crystalline amylose platelets and iodine-stained platelets,163 it was shown, following the suggestion of Hanes, that a helical configuration of the amylose in this complex is probable. This was later confirmed by x-ray measurements (see p. 378) the iodine atoms were shown to be situated in the core of helically-oriented amylose molecules. 

Although it has been found that the separated amylose component can be readily orientated to yield fiber patterns, amylopectin usually gives poor or amorphous patterns. In the granule, however, amylopectin does exhibit crystallinity, since waxy maize starch gives a diffraction pattern and other waxy starches behave similarly.193 -195 (This suggests that the branch points in the amylopectin molecule may be in the amorphous part of the granule.)... 

Birefringence (or double refraction) is the decomposition of a light ray into two rays when it passes through certain types of crystalline material. This occurs only when the material is anisotropic, that is, the material has different characteristics in different directions. Amylose and amylopectin polymers are organized into a radially anisotropic, semicrystalline unit in the starch granule. This radial anisotropy is responsible for the distinctive... 

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). 

FIGURE 5.8 Unit cells (outlined in each diagram) and helix packing in A and B polymorphs of starch. Reprinted from Carbohydrate Research, Vol. 61, Wu and Sarko (1978b), The double helical molecular structure of crystalline A-amylose, Pages 27-40, with permission from Elsevier. 

Cheetham, N. W.H. and Tao, L. (1998). Variation in crystalline type with amylose content in maize starch granules X-ray powder diffraction study. Carbohydrate Polymers. 36, 277-284. 

In the present work, we extend the method to compensate for the hydrogen bonds present in carbohydrates. The hydroxylated character of carbohydrate polymers influences between-chain interactions through networks of hydrogen bonds that occur during crystallization. Frequently, several possible attractive interactions exist that lead to different packing arrangements, and several allomorphic crystalline forms have been observed for polysaccharides such as cellulose, chitin, mannan and amylose. The situation is even more complex when water or other guest molecules are present in the crystalline domains. Another complication is that polysaccharide polymorphism includes different helix shapes as well. 

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