Fine structure of amylose

Abstract

Amylose is usually the second most abundant component of starch, accounting for typically 20–30 % of its weight. In contrast to the more abundant, highly branched amylopectin, amylose is generally recognized as a linear or slightly branched molecule, both of which are present in amylose prepared from native starch. The structure of amylose can be described in terms of its size and branching. The size of amylose differs depending on the source of the starch, with average degree of polymerization in the range of _1,000 to _5,000. The branching of amylose can be characterized as a whole, or for the branched components by several structural indices, including its “-amylolysis limit (70–90 %), average chain length (200–500), number of chains per molecule (5–20, for the branched molecules), and molar fraction of branched molecule (0.2–0.5). Debranching of amylose with isoamylase and/or pullulanase is incomplete (up to _80 %), but still the size distribution of the debranched product can be informative. The main chain of the debranched product is comparable in size to the native amylose. A small number of long side chains are present with a chain length of from several hundred to a similar length as the main chain. The vast majority of the side chains on a molar basis are short chains, which have a chain-length distribution similar to that of amylopectin. The side chains are not arranged in a cluster fashion, which is a common fundamental structural characteristic of amylopectin.