COMPOSITION AND STRUCTURAL-ANALYSIS OF ALPHA-DEXTRINS FROM POTATO AMYLOPECTIN

Potato amylopectin was hydrolyzed with the alpha-amylase of Bacillus a myloliquefaciens to produce intermediate a-dextrins with a degree of p olymerization < 1000. The products were then fractionated by methanol precipitation into samples of different size distributions that were a nalyzed by gel-permeation chromatography. All samples contained mixtur es of high and low molecular weight dextrins, but in different proport ions. Selected fractions were treated successively with phosphorylase and beta-amylase to obtain phi,beta-limit dextrins. A further alpha-am ylolysis of the limit dextrins was performed to investigate their comp ositions and suggested that the amylopectin was build up of structural ly different domains. The size of the units of clusters probably range d from dp 30-70. Dextrins of this size were only slowly hydrolyzed fur ther by the alpha-amylase and the long internal chains had been hydrol yzed 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 inve stigate the mode of interconnection of structural units in the amylope ctin. (C) 1996 Elsevier Science Ltd.