Structures of clusters in sweetpotato amylopectin

Sweetpotato amylopectin was subjected to partial hydrolysis by α-amylase from Bacillus amyloliquefaciens to release the clusters. Clusters were then fractionated and precipitated by methanol and structurally characterized by gel-permeation chromatography and high-performance anion-exchange chromatography. An initial stage of α-amylolysis on the amylopectin isolated mostly domains but also clusters. A second stage of α-amylolysis on the domains and clusters further isolated their respective clusters and sub-clusters. All the domains, clusters and sub-clusters were sequentially subjected to phosphorolysis and β-amylolysis to obtain their internal part. The degree of polymerization of the clusters in the form of φ,β-limit dextrins were from 58 to 86. Each domain contained 2–8 clusters. Two types of clusters were structurally identified. Type A clusters were larger and contained about 12 chains per cluster with higher degree of branching (DB), whereas those of type B were smaller and contained about eight chains per cluster with lower DB.

Possible structures of backbones in amylopectin clusters, → denotes α-(1→6)-linkages, the bold lines denote the backbones of clusters, the dashed lines denote the branches developed from backbones, slashed black spot denotes reducing end. (A) B2-chain (DP 25–57) as the major backbone and B1b-chain (DP 18–24) as a branch backbone developed from major backbone. (B) Two B1b-chains with equal chance being the major backbone.Figure optionsDownload as PowerPoint slide