Amylopectin molecular structure

Vermeylen, R., Goderis, B., Reynaers, H., and Delcour, J. A. (2004). Amylopectin molecular structure reflected in macromolecular organization of granular starch. Biorrmcromolecules 5,1775-1785. 

Molecular Structure. Most starches consist of a mixture of two polysaccharide types amylose, an essentially linear polymer, and amylopectin, a highly branched polymer. The relative amounts of these starch fractions in a particular starch are a major factor in determining the properties of that starch. 

Figure 8.4 Molecular structure of the amylose and amylopectin components of starch.

As described earlier in this book, the dendritic architecture is perhaps one of the most pervasive topologies observed at the macro and micro-dimensional length scales (i.e. jum-m). At the nanoscale (molecular) level there are relatively few natural examples of this architecture. Most notable are probably the glycogen and amylopectin hyperbranched structures that Nature uses for energy storage. 

Shibanuma et al.232 examined the molecular structures of starch isolated from three Japanese wheat varieties, one Australian standard white wheat and one US western white wheat. The data presented in Tables 10.9 and 10.10 again indicate that the properties and structural features of amylose and amylopectin are dependent on the starch source. The molecular sizes of amylose and amylopectin were larger in the US wheat compared to the corresponding starch fractions from the Australian and Japanese wheat starches. Among the five wheats, the two preferred for salt noodles in Japan, the Japanese variety Chihoku and the Australian standard white, contained a higher proportion of branched amylose and a lower number of chains per amylose... 

In many foods, both starch and protein can be encountered so that understanding interactions between them would be useful. The selectivity in interaction between proteins and starches is best seen in results of dynamic rheological studies. The results depend upon the molecular structure of protein, the starch state of the granules and the amylose/amylopectin ratio, the composition of protein and starch, as well as the phase transition temperatures are important factors influencing protein-starch interaction. Because proteins and starches are thermodynamically different polymers, their presence together may lead to phase separation, inversion, or mutual interaction with significant consequences on texture (Morris, 1990). 

Profound modifications and degradation of the molecular structure occur when starch granules, or their component amylose and amylopectin, are heated. The extent of the changes induced depends on the temperature and time involved, and, under extreme conditions, may result in a complete loss of carbohydrate character. 

Figure 3 Molecular structures of a-o-glucose and the two major molecules that make up starch, amylose, and amylopectin. 

FIGURE 29.1 The molecular structure of starch containing (a) amylose and (b) amylopectin. 

In contrast, the molecular structure of amylopectin is highly branched via 1,6-a linkages. The average degree of pol mrieriza-tion of the branches is about 25 monomer units. Due to the highly branched structure, the amylopectin molecules can not move as freely and do not align and associate as readily (1). 

Starch.—The molecular structures of unmodified and modified ((9-2-hydroxy-propyl di-starch phosphate) manioc starches have been investigated after fractionation of their pullulanase, j3-amylase, and/or glucoamylase hydro-lyzates. A model depicting the possible sites of 2-hydroxypropyl and/or phosphate groups on the modified manioc amylopectin molecule was presented. 

Figure 14.7 Molecular structure of (a) Starch amylose and (b) Amylopectin. Adapted from DP [40] (http //creativecommons.oig/licenses/by/3.0/legalcode)...

Starch is comprised of two major components, amylose and amylopectin. The former is composed of linear and branched molecules with very limited branches, and the latter is composed of highly branched molecules with hundreds or thousands of branches. Ibe branched component of amylose may be called an intermediate molecule or the third component (1 ). Hiese molecules are built up of cxily glucose but their molecular structures are not well elucidated yet, in spite of the many efforts by various investigators. Here, we present our recent findings on the molecular structure of amylopectin. 

FIGURE 11.4 Indicative molecular structures of amylose and amylopectin. 

Figure 6.22 Hierarchical structure of starch, (a) Whole granule (scale pm), (b) Growth rings ( 100s nm), (c) crystalline and amorphous lamellae ( 9 nm) and (d) molecular structure of amylopectin ( A). [Reproduced with permission from T. A. Waigh, Applied Biophysics, John Wiley Sons. Copyri t (2007) John Wiley Sons Limited]...

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