Small differences in amylopectin fine structure may explain large functional differences of starch

• Internal chain length is critical for amylopectin functional properties.
• Very short chains may affect functional properties of amylopectin.
• Minor structural differences of amylopectin influence on its properties.
• Intermolecular internal and external segments of amylopectin form complexes.

Four amylose-free waxy rice starches were found to give rise to gels with clearly different morphology after storage for seven days at 4 °C. The thermal and rheological properties of these gels were also different. This was remarkable in light of the subtle differences in the molecular structure of the amylopectin in the samples. Addition of iodine to the amylopectin samples suggested that not only external chains, but also the internal chains of amylopectin, could form helical inclusion complexes. It is suggested that these internal helical segments participate in the retrogradation of amylopectin, thereby stabilising the gels through double helical structures with external chains of adjacent molecules. Albeit few in number, such interactions appear to have important influences on starch functional properties.