Molecular weight of amylose

From osmotic pressure measurements, the molecular weight of amylose has been determined as approximately 10,000-50,000. This value is well in line with the value estimated from the determination of the terminal functional groups. 

Swinkels29 collected published characterization data for tapioca starch and compared it to that for other starches of commercial significance (Table 12.4). Tapioca starch is differentiated from other starches by its low level of residual materials (fat, protein, ash), lower amylose content than for other amylose-containing starches, and high molecular weights of amylose and amylopectin. The small amount of phosphorus in tapioca starch is partially removable30 and, therefore, not bound as the phosphate ester as in potato starch. It is also common to find protein and lipid values of zero, as reported by Hicks.31 The very low protein and lipid content is an important factor which differentiates tapioca starch from the cereal starches. 

About 75% of the sizing agents used throughout the world today consist of starch and its derivatives because of its low cost. Chemically starch is composed of amylose and amylopectin. Amylose molecule is in the form of helix with six glucose units per turn (Fig. 3-1). The low molecular weight of amylose is water soluble... 

Typical molecular weights of amylose are around one million and amylopectin around ten million. The amylose and amylopectin molecules are in an ordered arrangement widiin the granule and gives crystallinity to the granule. 

Amylose is a linear polymer with 200-2000 a-D-glucopyranosyl units linked by a-(l,4 ) glycosidic bonds. The molecular weight of amylose from various sources ranges from 40,000 to 400,000. When we say that a polymer is linear, we do not mean that the polymer chain travels in a straight line, but that is has no branches. In fact, amylose coils into a helix. Figure 26.12 shows a three-residue fragment of amylose. 

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