Composition and structural analysis of alpha-dextrins from potato amylopectin

Potato amylopectin was hydrolyzed with the alpha-amylase of Bacillus amyloliquefaciens to produce intermediate α-dextrins with a degree of polymerization < 1000. The products were then fractionated by methanol precipitation into samples of different size distributions that were analyzed by gel-permeation chromatography. All samples contained mixtures of high and low molecular weight dextrins, but in different proportions. Selected fractions were treated successively with phosphorylase and beta-amylase to obtain /gf,β-limit dextrins. A further alpha-amylolysis of the limit dextrins was performed to investigate their compositions and suggested that the amylopectin was build up of structurally different domains. The size of the units of clusters probably ranged from dp 30–70. Dextrins of this size were only slowly hydrolyzed further by the alpha-amylase and the long internal chains had been hydrolyzed into chains of intermediate lengths. The ratio of A:B-chains and of A:Ba-chains increased with decreasing size of the dextrins, whereas Ba:Bb-chains decreased. The changes in the ratios can be used to investigate the mode of interconnection of structural units in the amylopectin.