The degree of starch phosphorylation is related to the chain length distribution of the neutral and the phosphorylated chains of amylopectin

The chain length distribution of the amylopectin neutral and phosphorylated α-glucan chains of isoamylase (EC 3.2.1.68)-debranched starch in dependence of starch phosphorylation has been analyzed using high performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Neutral chains of moderately phosphorylated starches showed polymodal distributions with main peaks at dp (degree of polymerisation) 14–15 and 50, respectively. Highly phosphorylated starches specifically showed an increasing proportion of chains with mean dp 19. In the extremely highly phosphorylated curcuma (Curcuma spp.) starch, this chain population dominated the chain length profile. The sub-population of the corresponding phosphorylated chains from highly phosphorylated starches showed longer retention times than moderately phosphorylated starches on HPAEC. Separation of the phosphorylated chains using anion-exchange chromatography at neutral pH demonstrated a partial separation of chains containing Glc3P residues and Glc6P residues, respectively, as well as a separation of chains containing one or several phosphate groups. Major determinants for the observed elution characteristics of phosphorylated chains using HPAEC are suggested to be a combination of chain length (as determined by gel-permeation chromatography), multiple phosphorylation of the chains (as determined from their content of Glc6P and reducing ends) and finally, the presence of the phosphate group on either the C-3 or the C-6 position on the glucose moieties (as determined by 31P NMR). The results demonstrate that general rules exist in the relationship between starch phosphorylation and chain length distribution of starches.