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How is the assembly of crystalline lamella influenced by the molecular structure of amylopectin?
V. VAMADEVAN (1), E. Bertoft (1), K. Seetharaman (1). (1) University of Guelph, Guelph, ON, Canada

The structure of amylopectin is characterized by the unit chain length profile and the nature of branching pattern, which determines the alignment of glucan chains during biosynthesis. Numerous studies have investigated the unit chain profile of amylopectin and their impact on starch structure and functional properties. However, the structural basis for the functional properties of starches from different botanical origin is poorly understood. Internal unit chain profile of amylopectin from a different botanical sources have demonstrated that the nature of the branching pattern, which includes the distance between the branching points within the cluster (IB-CL), the number of branched building blocks (NBbl), and the size of the clusters, plays a crucial role in determining the architecture of the granule. The relationship between the internal unit chain profile and thermal and annealing behavior of starches from four different groups of amylopectin was investigated. Amylopectin clusters with a higher number of chains, more frequent branching, and shorter external chains showed lower melting temperature and enthalpy, and higher susceptibility to annealing. The results highlighted that (i) the NBbl and IB-CL within the clusters influence the packing of double helices within the crystalline lamellae (ii) shorter distances between the branching points within the cluster enhance the number of unpacked double helices within the crystalline lamellae and (iii) longer external chains increase the numbers of splayed double helices, which are not paralleled packed within the crystalline register. A model was proposed based on the backbone concept of amylopectin structure that explains how the organization of chains in the semicrystalline lamellae relates to the thermal properties. The validity of the model was tested by annealing.

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