Amylopectin internal molecular structure in relation to physical properties of sweetpotato starch

Unit chain length distributions of amylopectins and their φ,β-limit dextrins (reflecting amylopectin internal part) from 11 Chinese sweetpotato genotypes were characterized by high performance anion-exchange chromatography after debranching, and were related to the thermal and pasting properties of granular starches. The weight-based unit chain length profiles of whole amylopectin and their internal parts both had three distinguishable major groups with approximate range of DP 6-36, 37-68, and >69 for amylopectins and DP 3-25, 26-55, and >55 for φ,β-limit dextrins. Among different genotypes, two different patterns of B_fp (fingerprint B-chains, DP 3-7) were observed for φ,β-limit dextrins, whereas A_fp (fingerprint A-chains, DP 6-8) for whole amylopectins were consistent. Reconstruction of amylopectins from their φ,β-limit dextrins revealed that B-chains with internal DP > 20 possessed an external chain length corresponding to the average value DP 12.8. Wide genetic variations were recorded among structural parameters, of which several concerning the amylopectin internal part were highly correlated to the thermal and pasting parameters of sweetpotato starches, and suggested that the internal part of amylopectin is critical to the physical behavior of granular starch.