Chapter 13: Highly Branched Cyclic Glucan-based Systems

Highly branched cyclic glucan (HBCG) or cyclic amylopectin (CA) is a new type of dextrin that is produced from amylopectin via cyclization reaction of a branching enzyme. HBCG is a white odourless powder in which the structural units consist of α-d-glucose monomers. HBCG is made of at least 80% highly-branched cyclic dextrin molecules, which are characterized by a molecular weight ranging from 30 000 to 1 000 000 and a weight-average degree of polymerization of 2500 glucose units. The dextrose equivalent (DE) value of HBCG, a measure of the reducing power (d-glucose), is <5 (the DE value of dextrose is 100). The short linear chains of HBCG are composed of α-(1 → 4)-linked glucose units with branching occurring via α-(1 → 6) glucosidic bonds, while the ring structure (or cyclic α-glucan moiety) is formed by an α-(1 → 6) linkage between the terminal glucose of a free chain and a non-terminal glucose in another chain and is composed of 16 to 100 α-linked glucose units. HBCG also contains less than 3.5% of single glucose molecules, and approximately 10% of other saccharide molecules that are either smaller or larger than HBCG.