Characterization of dextrins obtained by enzymatic treatment of cationic potato starch

摘要

The substitution pattern of cationic potato starches was studied using starch hydrolyzing enzymes and a characterization of the hydrolysis products. Native and cationic starch samples were hydrolyzed with pullulanase, isoamylase, and alpha-amylase and the molecular-weight distributions of the resulting dextrins were studied using gel permeation chromatography. Isoamylase hydrolyzed the native potato starch sample readily, whereas hydrolysis with pullulanase was incomplete. Pullulanase hydrolyzed, however, cationic starch with higher DS (degree of substitution) more efficiently than isoamylase. The hydrolysis products obtained with pullulanase were separated according to charge using cation-exchange chromatography into one unbound and two bound fractions. The unbound fraction possessed an increasing number of short chains from amylopectin with increasing DS of the starch sample. The bound material contained amylose and dextrins with sizes corresponding to the long B-chains. The high portion of uncharged dextrins after alpha-amylolysis suggested that the substitution pattern, on the molecular level, was non-random. The composition of the unbound and bound material, obtained by ion-exchange chromatography of alpha-amylase treated starches, suggested a more intense fragmentation with increasing DS of the sample. Possibly, the substituents influence substrate conformation and thereby alter the hydrolysis patterns. It is concluded that a thorough understanding of the enzymatic hydrolysis patterns is of ultimate importance in structural studies of modified starch.