Characterisation of fractions obtained by isoamylolysis and ion-exchange chromatography of cationic waxy maize starch

Isoamylase hydrolysates of wet- (WC) and dry-cationised (DC) waxy maize starch were fractionated by ion-exchange chromatography on CM-Sepharose into an unbound and four bound fractions. The amount of bound dextrins was higher in the WC than in the DC sample. The fractions were characterised by gel-permeation chromatography and proton-NMR spectroscopy. The unbound fraction from the WC sample consisted mainly of linear chains formed from amylopectin. The dextrins in the bound fractions contained increased amounts, from 1.2-7.9, of cationic substituents per molecule and the degree of polymerisation increased with the density of substituents. Dextrins weakly bound to CM-Sepharose had a linear structure, whereas more tightly bound fractions were mixtures of linear and branched dextrins. In the latter, the debranching was incomplete because of sterical hindrance by substituents at or close to the branch points. Most of the dextrins were partly hydrolysed by beta-amylase, but the more highly substituted fractions possessed also a population of beta-amylase resistant dextrins, suggesting substituents at the non-reducing ends.