Definition -
Amylopectin is a polymer of several D-glucose molecules. 80% of amylopectin is present in starch. Amylopectin molecules are linked by α-1,4-glycosidic bonds and α-1,6-glycosidic bonds. It is a water-insoluble fraction.
Heating starch with water produces a colloidal suspension due to the swelling of starch granules. It readily dissolves in hot water. On cooling, it forms a starch paste or starch gel.
Amylopectin, the major glucan of most starches (75–85%), is composed of a highly branched molecular structure. Individual linear sub-chains are formed from anhydroglucose monomers joined by α1-4 bonds, terminating in a non-reducing end. Branch points (4–5%) are induced at position O-6 of glucose units by formation of an additional α1-6-linked glucose monomer in a chain, which is elongated again by α1-4 linked glucan chains on pre-existing chains. The average chain length in amylopectin is 20–30 monomers and the degree of polymerization (DP) is around 10000–100000. Due to formation of molecular aggregates between individual amylopectin molecules, it is still difficult to obtain accurate molecular weights of amylopectins found in starches from different botanical origin. Mw values range between 200 and 700 × 106 depending on source and method of determination.6–8 Mn values are much lower. Due to the highly branched structure, several alternative structural models for amylopectin have been proposed. The nomenclature developed to describe the structure differentiates between three types of structure-building (1-4)-α-D-glucan chains: A-chains are unsubstituted chains linked to the molecule by their reducing ends, B-chains are linked by their reducing end to the molecule and are substituted at one or more of glucose units at position O-6. B-chains may be further subdivided into subtypes depending on special structural details of the branching chains. C-chains are those chains terminating in a reducing group .