Amylose is a type of starch that is composed of linear chains of glucose molecules. It is an important component of plant-based foods such as potatoes, rice, and corn. Amylose is less readily broken down by digestive enzymes than the other type of starch, amylopectin, which means it provides a slower release of energy and helps to regulate blood sugar levels.
Amylose is an almost linear, water-soluble polysaccharide with α-D-1,4- anhydroglucose linkages. The molecular weight of amylose is 105-106 Da. The molecular size depends on the source and it may contain anywhere from about 200 to 2000 anhydroglucose units. Because of its linearity, mobility and hydroxyl groups, the amylose polymers have a tendency to orient themselves in a parallel fashion where hydrogen bonds can be formed between adjacent polymers. This phenomenon of intermolecular association is commonly called retrogradation (Wurzburg 1986) and as a result the amylose gels become opaque.
Although it is said that amylose is linear, it is well established that there is some branching on the molecule. These few branches do not influence the hydrodynamic behavior of amylose (Buléon et al. 1998). The configuration of amylose is still open to debate (Whistler et al. 1984) but it is said that in water, amylose exists as a random coil, whereas in a good solvent (e.g. dimethylsulphoxide) it exists as an extended coil. In the presence of a complexing agent (e.g. I2 or lipids) amylose exists as a helix.
Amylose exists in the crystal structures A, B, C, and V. The B-amylose, as in potato starch, is helical with an integral number of α-D-glucopyranosyl residues per turn. The configuration of amylose in solution has been debated for many years. The range of models in solution varies from helical (stiff, rod-like or loosely wound, worm-like) and interrupted helix to a random coil. The V-structure can occur after the gelatinization of the starch since amylose forms a complex with fatty acids, lipids and other polar molecules.
The nowadays accepted models for A and B amylose structures are based upon 6- fold, left-handed double helices with a pitch height of 2.08-2.38 nm. In the B-type structure, double helices are packed with the space group P61 in a hexagonal unit cell (a=b=1.85 nm, c= 1.04 nm) with 36 water molecules per unit cell. The symmetry of the double helices differs in A and B structures since they have different repeating units.
Potato starch contains between 18 and 21% amylose (Wurzburg 1986; Buléon et al., 1998) and the potato starches used in this work have been based on native potato starch with an amylose content of about 20% analyzed by size-exclusion chromatography (Svegmark et al. 2002). Due to its linear character, amylose can crystallize and films of amylose thus have better barrier properties and show higher modulus than amylopectin films (Forssell et al. 2002; Rindlav-Westling et al. 1998, Rindlav et al. 1997).