Starch

Starch is one of the major components or cereal grains. Commercially important starches come from corn, waxy corn, high amylose corn, wheat, rice, potato, tapioca, and pea. The major sources of commercial starch here in Thailand are tapioca and rice. The starches are readily obtained from these plant source as a fine powder (granular starch) consisting of spherical or ellipsoidal grains ranging in particle size from 3 to 100 μm. Among these, rice starch has among the smallest granule size and potato starch the largest of all starch types. (Kirk and Othmer, 1997)

Starch (David, 1998) is predominantly composed of two polymers of D-glucose, amylose and amylopectin. Amolose is a lightly branched polymer comprised of α-1,4 linked anhydroglucose units and has molecular weights which vary from 10⁵- 10⁶. Amylose from different sources contains, on average, two to eight α-1,6 branch points per molecule. Amylopectin is a highly branched molecule consisting of short (15-45 residues)  α-1,4 oligomers linked by α-1,6 bonds. The overall structure is thought to be tree-like. Molecular weights range from 10⁷- 10⁹ with the average over 10⁹. Whithin the native starch granules, amylopectin is partially crystalline while amylose is amorphous (non-crystalline). The native crystalline structure of amylopectin consists of parallel-stranded double helices with six glucose units per 2.1 nm. rise in each individual strand.