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Starches ......... Amylopectin ......... Amylose .......... Structure ............ Pathway .......... Mutants ............ Enzymes .......... Clones ........... Modifications ............ Functionality .......... EnCapsulation ........... Processing


Starch Structure.

Text from Keeling (©1998)

Starch is a stored in plants as a semi-crystaline granule composed of a highly ordered polymer of glucose. In most cases it is a mixture of 25% amylose and 75% amylopectin.

Amylose is linear a1,4-glucan with a few branch points, whilst amylopectin is a highly branched chain of a1,4- and a1,6-glucan chains. Naturally occuring mutants are known with low amylose content and there are other natural mutants with higher (e.g. from 50-90% amylose) than normal levels of amylose. In cereal plants the starch is laid down in the endosperm tissue of the grain. In potato the storage organ is the tuber. In tomato and many other fruits, starch is laid-down transiently before ripening, during ripening the starch is degraded back to sucrose. Starch derived from corn grain during wet-milling can be isolated in a remarkably pure state, contaminated only by a small percentages of proteins and lipids. Starch from all species has a very minute fraction of phosphorylated glucans with potato tubers carrying the highest known percentage (100 times higher than all cereals).