Structure of Branched Subunits in the Amylopectins of Starches Varying in Polymorphism

Amylopectins from model starches of different polymorphisms (A-type maize, C_A-type lotus seed, and B-type potato) were characterized with regard to the molecular structure of their branched subunits (clusters and building blocks). Lotus seed and maize clusters had larger sizes, shorter average chain lengths, higher branching densities, and shorter interblock chain lengths than potato clusters. Lotus seed and maize clusters were different in their composition of short internal chains. Lotus seed clusters consisted of fewer singly branched blocks and more doubly branched blocks than maize clusters. The clusters isolated from the two lotus seed amylopectins had similar chain length distribution but different building block compositions. The interbranch chain length was considered important in shaping starch polymorphism. Starch polymorphism might be related not only to the densely branched subunits of amylopectin but also to the loosely branched ones. In addition, this study exemplified a light-scattering-based method as an alternative for the size characterization of amylopectin branched subunits.