Composition of clusters and their arrangement in potato amylopectin

The cluster structure of amylose-free potato starch was investigated in detail. Groups of clusters (structural domains) were produced by α-amylolysis and size-fractionated by methanol precipitation. The domains were then further hydrolysed with α-amylase until free clusters were released. In the form of ϕ,β-limit dextrins the clusters possessed mainly DP around 70 and 50–55, but a minor group of very small clusters were of DP 25. In order to release the clusters, the α-amylase hydrolysed long B-chains into shorter B1b-chains. In the initial stages of hydrolysis small, branched fragments were released, possibly from branched structures outside the clusters. In domain structures composed of two clusters a B2-chain was involved in their interconnection, but when the number of cluster increased, the number of long B2- and B3-chains was apparently higher than predicted from the generally accepted cluster model. The two-directional backbone model offered a possible solution for the interconnection of groups involving several clusters.