Critical examination of the characterization techniques, and the evidence, for the existence of extra-long amylopectin chains

It has been suggested that amylopectin can contain small but significant amounts of extra-long chains (ELCs), which could affect functional properties, and also would have implications for the mechanism of starch biosynthesis. However, current evidence for the existence of ELCs is ambiguous. The amylose/amylopectin separation and the characterization techniques used for the investigation of ELCs are reviewed, problems in those techniques are examined, and studies of ELCs of amylopectin are discussed. A model for the biosynthesis of amylopectin chains in terms of conventional biosynthesis enzymes, which provides an excellent fit to a large amount of experimental data, is used to provide a rigorous definition of ELCs. In addition, current investigations of ELCs, involving separation, is hindered by the lack of a method to quantitatively separate all the amylopectin from starch without any traces of residual amylose (which would have long chains). Unambiguous evidence for the existence of ELCs can be obtained using two-dimensional (2D) characterization, these dimensions being the degree of polymerization of a chain and the size of the whole molecule. Available 2D data indicate that there are no ELCs present in currently detectable quantities in native rice starches. However, concluding this more rigorously requires improvements in the resolution of current 2D methods.

Automated summary

This paper discusses the impact of extra-long chains (ELCs) on the functional properties and biosynthesis mechanism of starch. However, the evidence for the existence of ELCs is currently uncertain. The paper reviews the techniques for separating amylose/amylopectin and characterizing ELCs, and discusses the related studies. A model based on conventional biosynthesis enzymes is used to provide a rigorous definition of ELCs. The lack of a method to quantitatively separate all amylopectin without residual amylose hinders current investigations. Two-dimensional (2D) characterization can provide unambiguous evidence for the existence of ELCs, but the resolution of current methods needs improvement for more accurate conclusions.