Crystallization amylopectin

Starches with high amylose content, such as corn starch (28% amylose) retrograde more than starches with lower amylose content, such as potato starch (20% amylose). Redispersion of retrograded starch is energy-intensive due to extensive bonding. Temperatures of 115° to 120°C are required to solubilize amylose gels or crystals. Amylopectin gels can be redispersed at temperatures above 55°C. 

Amylase operates exclusively on nonreducing, terminal units in amylose or on the branches in amylopectin, to produce maltose directly, and its hydrolytic action on 4 — 1-a-D linkages is stopped by any branch points. Enzyme action is greatly impeded by secondary valence forces, as retro-gradation, for example, is accompanied by an increased resistance to j8-amylolysis.19 The enzyme can be crystallized relatively easily. The mode... 

X-ray diffraction studies support the double-helical structure but suggest a parallel orientation of the amylose chains.81 Since amylose has not been obtained as single crystals the diffraction data do not give a definitive answer. However, if double helices are formed by adjacent branches in amylopectin and glycogen the two strands would be parallel. Starch granules also contain amorphous starch which appears to contain single helices, possibly wrapped around lipid materials.82... 

Because the varieties of starch that contain only amylopec-tin are also crystalline, exhibiting the same diffraction patterns as starches containing amylose, there is a strong likelihood that the extensively branched amylopectin molecule also crystallizes in a double-helical form. In turn, this implies that linear sequences in amylopectin remain sufficiently long to... 

Using results of these kinds of studies, the characteristic structure of amylose can be differentiated from that of amylopectin. Amylose has a small number of branches and crystallizes and precipitates when complexed with 1 -butanol. The iodine affinity of amylose is much greater (i.a. 18.5 to 21.1) than that of amylopectin (i.a. 0.0 to 6.6),79,152-158,163,169-174 and the iodine affinity of amylose (3-limit dextrin is similar to that of the parent amylose. The average chain length of amylose (3-limit dextrins is much larger than that of the amylopectin (3-limit dextrin.160... 

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