Chapter 2 - Analyzing Starch Molecular Structure

Abstract

Starch consists of two major molecular components, amylose and amylopectin. In addition some plants, especially plants with a modified starch biosynthesis, also contain materials with structures intermediate to amylose and amylopectin. Diverse methods for the analysis of the structure of these components are presented in this chapter. For a detailed analysis, the components generally have to be separated e.g. by utilizing the complex formation between amylose and butanol or alternatively the complex formation between amylopectin and concanavalin A. The separation may also be made using a suitable chromatographic method, such as gel-permeation chromatography. After this step the fine structure analysis is preferentially made using enzymes that perform specific and controlled degradation of the macromolecules. These enzymes are generally divided into three groups, namely debranching enzymes, which attacks (1→6)-linkages, exo-acting enzymes, which hydrolyses glucose or maltose from the non-reducing ends of the molecules until a limit dextrin remains, or endo-acting enzymes, which attacks (1→4)-linkages at internal chain segments. The first group is used for analysis of the unit chain distribution of starch components. The second group enables estimation of the external chain lengths and internal chain distribution analysis. The third group is used to isolate the branched structural units of amylopectin, which enables a detailed analysis of the branching pattern in this extensively branched polysaccharide.