Fine structure characterization of amylopectins from grain amaranth starch.

The aim of this study was to determine the fine structure of amylopectin from grain amaranth. Amaranthus amylopectin was hydrolyzed with alpha-amylase, and single clusters and a group of clusters (domain) were isolated by methanol precipitation. The domain and the clusters were treated with phosphorylase a and then beta-amylase to remove all external chains, whereby the internal structure was obtained. The phi,beta-limit dextrins were analyzed on Sepharose CL 6B. The average DP (degree of polymerization) and peak-DP values of fractions of clusters were 57 and 82, respectively; the values of the domain were 137 and 309, respectively. The unit chain length profiles were analyzed by high-performance anion-exchange chromatography with pulsed amperometric detector (HPAEC-PAD). The results showed that the domain fraction contained approximately 2.2 clusters, and single clusters were composed of approximately 13 chains. The phi,beta-limit dextrins of the clusters were further hydrolyzed with alpha-amylase to characterize their building block composition. The average DP of the branched blocks was approximately 11 and they contained on average approximately 2.5 chains. Their average chain length, internal chain length, and degree of branching were approximately 4.3, 2.8, and 14, respectively. A cluster consisted of approximately 6 branched blocks, and the internal chain length between the blocks was approximately 6.8.