Thermal and rheological properties of granular waxy maize mutant starches after isoamylase modification

This work investigated the changes in the thermal and rheological property of two waxy maize mutant starches (Hsyn73 wxwx and Hsyn73 duwx) after they were treated with isoamylase in the granular state for various periods. The hydrolysis degrees reached in 168 h were 4.0% and 9.5% for the wxwx and the duwx, respectively. With increasing degree of hydrolysis, both wxwx and duwx generally showed an increase in gelatinization and retrogradation temperatures and retrogradation enthalpy. The weight average molar mass (M_w), z-averaged radius of gyration (R_z), and pasting viscosity of both starches decreased when isoamylase hydrolysis progressed, however, the wxwx showed a greater decrease in M_w and R_z than the duwx at the same hydrolysis degree. Both wxwx and duwx, native or isoamylase-treated, displayed a similar pasting viscosity during holding and cooling when their amylopectin molecules had a similar R_z. The study indicates the importance of R_z in determining the pasting properties of waxy maize starch.