Structures of building blocks in clusters of sweetpotato amylopectin

φ,β-Limit dextrins of domains and clusters of sweetpotato amylopectin were subjected to extensive hydrolysis by Bacillus amyloliquefaciens α-amylase to release building blocks and reveal the internal structures of clusters. The composition of building blocks was analyzed by size-fractionation, gel permeation chromatography, and high performance anion exchange chromatography. Different domains and clusters had structurally similar building blocks with around three chains per building block and internal chain length around 2.9. Singly branched and doubly branched building blocks were the largest and second largest groups in the clusters. Type A clusters had more large building blocks and contained 5–6 blocks per cluster with an inter-block chain length (IB-CL) of 7.0, whereas type B clusters had less large building blocks and contained 3–4 blocks per cluster with IB-CL 7.9. Models on how the building blocks could be organized into type A and type B clusters are discussed.

Graphical abstractPossible influence of building block size on the amorphous region in starch granule: Black cylinders symbolize the double-helix in the crystalline lamellae. Gray circles denote building blocks. A: Two chains from one building block with internal chain length of three interact to form a double helix with little twisted amorphous region. B: Two building blocks are close in space, but separated by a longer chain (bold line), which contributes to the formation of more twisted amorphous region.Figure optionsDownload full-size imageDownload as PowerPoint slide