Starch structure and functionStarch is the major energy storage compound in higher plants. The name starch represents semicrystallinic particles composed exclusively of glucose residues. The glucose moieties are linked by only two types of bonds: α-1,4 and α-1,6 glucosidic linkages. The main constituents of starch are amylopectine (~75% by weight), and amylose (~25% by weight) (Blennow et al., 2002). Amylopectine is a semicristalline, highly branched polysaccharide with an α-1,4 backbone and 4-5% α-1,6 branch points (Ball et al., 1998). The degree of polymerisation of amylopectine is 103-104. Amylose is amorphous and is composed mainly of linear chains of α-1,4 linked glucose units with less than 1% α-1,6 branch points (Ball et al., 1998). The degree of polymerisation of amylose is 102-103. The starch particle also contains proteins, lipids and phosphate, but at a very low concentration (Buleon et al., 1998). The only naturally occurring covalent modification of starch is phosphorylation. About 1/300 glucosyl residues in potato starch are normally phosphorylated on the six-or-three-position; in cereal and leaf starches, the level of phosphorylation is considerably lower than this (Blennow et al., 2000; Smith et al., 2003).