Structures and Physicochemical Properties of Acid-Thinned Corn, Potato and Rice Starches

The structures and physicochemical properties of acid-thinned corn, potato, and rice starches were investigated. Corn, potato, and rice starches were hydrolyzed with 0.14 N hydrochloric acid at 50 °C until reaching a target pasting peak of 200—300 Brabender Units (BU) at 10% solids in the Brabender Visco Amylograph. After acid modification the amylose content decreased slightly and all starches retained their native crystallinity pattern. Acid primarily attacked the amorphous regions within the starch granule and both amylose and amylopectin were hydrolyzed simultaneously by acid. Acid modification decreased the longer chain fraction and increased the shorter chain fraction of corn and rice starches but increased the longer chain fraction and decreased the shorter chain fraction of potato starch, as measured by high-performance size-exclusion chromatography. Acid-thinned potato starches produced much firmer gels than did acid-thinned corn and rice starches, possibly due to potato starch's relatively higher percentage of long branch chains (degree of polymerization 13—24) in amylopectin. The short-term development of gel structure by acid-thinned starches was dependent on amylose content, whereas the long-term gel strength appeared dependend on the long branch chains in amylopectin.