Structures and rheological properties of corn starch as affected by acid hydrolysis

Common corn starch was treated with different concentrations of hydrochloric acid, 0.06, 0.14, and 1.0N, for different lengths of time, 18, 6, and 1 h, respectively, to reach a similar peak viscosity as measured by Brabender Viscoamylograph. The fine structures, crystallinity and thermal properties were characterized and the rheological properties were evaluated using both compression and dynamic oscillatory tests. Acid hydrolysis had little effect on amylopectin branch chain-length distribution, gelatinization and retrogradation properties. However, the higher acid concentration (1.0N) degraded both amylopectin and amylose to a greater extent compared with the other two lower acid concentrations (0.06 and 0.14N). The acid treated starches had slightly higher degrees of crystallinity and lower amylose content than did the unmodified starch. Degradation of amylose and amylopectin by a high acid concentration resulted in a decrease in storage modulus (G′), loss modulus (G″), gelling temperature, and gel strength of the acid-thinned starches.