Susceptibility of annealed starches to hydrolysis by α-amylase and glucoamylase

The objective of this work was to determine if annealing altered the susceptibility of different starches to enzyme hydrolysis. Five commercial starches, including waxy corn, common corn, Hylon V, Hylon VII, and potato, were annealed by a multiple-step process, and their susceptibility to α-amylase and glucoamylase and the physicochemical properties of the hydrolyzed native and annealed starches were determined. During 36 h of enzyme hydrolysis, significant differences were noted between annealed starch and its native counterpart in the extent of α-amylolysis for Hylon V, Hylon VII, and potato, and in the extent of glucoamylolysis for potato. Waxy and common corn starches were hydrolyzed to a greater degree by both enzymes when compared with the other starches. The apparent amylose content of both native and annealed starches decreased during α-amylolysis for all starches, but increased for Hylon V, VII, and potato starches during glucoamylolysis. Most native and annealed starches exhibited comparable or increased peak gelatinization temperatures and comparable or decreased gelatinization enthalpy on hydrolysis with the exception of annealed potato starch, which showed a significant decrease in peak gelatinization temperature on hydrolysis. Annealed starches displayed significant higher peak gelatinization temperatures than their native counterparts. The intensity of main X-ray diffraction peaks of all starches decreased upon hydrolysis, and the changes were more evident for glucoamylase-hydrolyzed starches. The annealing process allowed for a greater accessibility of both enzymes to the amorphous as well as the crystalline regions to effect significant changes in gelatinization properties during enzyme hydrolysis.