An experimentally-based predictive model for the separation of amylopectin subunits during starch gelatinization

Starch granules in excess water gelatinize in a predictable manner, where radial and tangential expansion displaces amylopectin units from granular rings as a gradual centrifugal process concluding at the granular surface. Amylopectin appears as ellipsoidal particles in waxy maize starch granules in excess water at ambient temperature and swell to spherical particles on heat application. During swelling, the amylopectin units in waxy starches remain aligned along granular rings prior to displacement. This transient stage is absent in amylose-containing starches, suggesting packing of amylose between amylopectin molecules interferes with intermolecular amylopectin interactions. Loss of granular crystalline order, as determined by loss of birefringence, is a result of displacement of amylopectin units from granular rings. The granular surface encloses the structural amylose and amylopectin and modulates gelatinization endotherms. Chemical modifications of starches were also shown to alter the sequence of molecular events during gelatinization to give predictable changes. (C) 1998 Elsevier Science Ltd. All rights reserved.