Amylopectin molecular compositions

Starch is generally composed of 10—30% amylose and 70—90% amylopectin the composition varies depending on the geological area where the starch is produced as well as the plant variety. Cellulose is most commonly contained in cell walls and is distinguished from other polysaccharides produced by plants by its very long molecular chain. 

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). 

Insofar as the monosaccharides do occur as such in nature, it is more common to find the sugars occurring naturally in pairs (disaccharides) or in threes (trisaccharides) and, more likely, as the high-molecular-weight polysaccharides (Table 3.7). It is the polysaccharides which most probably contribute to the source material, especially the two well-known polysaccharides cellulose and starch. The fibrous tissue in the cell wall of plants and trees contains cellulose and starch also occurs throughout the plant kingdom in various forms but usually as a food reserve. The chemical composition of starch vanes with the source but in any one starch there are two structurally different polysaccharides. Both usually consist entirely of glucose units but one is a linear structure (amylose) whereas the other is a branched structure (amylopectin). 

Figure 22.13 A molecular model of amylopectin, a plant starch. Each sphere represents a glucose monomer. The monomers are linked in linear chains by a(l — 4) bonds, and branches occur every 24 to 30 glucose units via j8(l — 6) bonds. Glycogen, or animal starch, has the same composition and structure except that branching occurs every 8 to 12 glucose units. 

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