Granules, amylopectin

Behavior of Ground Starch and Amylopectin Granules with Respect to Organic Dyes7"... 

Composite gels amylopectin granules threaded by a gelled amylose matrix... 

Amylose Amylopectin Granules Crystallinity Hydrogen bonding Hydrophobic bonding Isolation Fractionation Gelatinization Solubilization... 

This structure for the granule is generally consistent with the x-ray diffraction data as yet available. However, it is difficult to envisage how amylopectin molecules possessing the three-dimensional structure suggested by Meyer (see p. 353) can align themselves to form any proportion of crystalline regions molecules with an essentially two-dimensional structure (as mentioned above) could do so far more readily. 

A similar structure has been given by Baker and Whelan,22 in which the granule is regarded as being built up of alternate layers of amylose and amylopectin, the thickness of the amylose layer decreasing from the center of the granule. This hypothesis has been criticized by Badenhuizen.22 ... 

The labile nature of the components necessitates that, for fundamental investigations, the starch should preferably be extracted from its botanical source, in the laboratory, under the mildest possible conditions.26 Industrial samples of unknown origin and treatment should not be used. The characterization of the starch would appear to entail (1) dissolution of the granule without degradation, (2) fractionation without degradation, (3) complete analysis of the finer details of structure of the separated components (including the possibilities of intermediate structures between the extremes of amylose and amylopectin), and (4) the estimation of the size, shape, and molecular-weight distribution of these fractions. 

Kerr181 has suggested that treatment of maize starch granules with 0.1 to 0.15 N sulfuric acid results in preferential degradation of the amylopectin,... 

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.)... 

Pea starch granules are oval, sometimes fissured, with a diameter of 20-40 ym (13). Molecular and structural characteristics of the two main components of field pea starch—amylose and amylopectin—are important in determining functional properties (25,26). Smooth field pea starch concentrate contains 97.2% starch of which 30.3-37.8% is amylose (9,23,25-27), and wrinkled pea starch concentrate contains 94.8% starch, which is 64% amylose (26). The gelatinization temperature of smooth pea starch is between 64 to 69 C, and that of wrinkled pea starch is greater than 99 C to 115 C. Gelatinization temperature depends on maturity of field pea seed and amylose content (26,27). 

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). 

Starch granules are composed of two types of a-glucan, amylose and amylopectin, which represent approximately 98-99% of the dry weight. The ratio of the two polysaccharides varies according to the botanical origin of the starch. 

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