2001 AACC Annual Meeting Charlotte, North Carolina October 14-18, 2001 Charlotte Convention Center

The structures and physicochemical properties of acid-thinned corn, potato, and rice starches were investigated. Starch structures were analyzed by high-performance size-exclusion chromatography and high-performance anion-exchange chromatography with pulsed amperometric detection; physicochemical properties studied included pasting, gelling, and thermal properties. Corn, potato and rice starches were treated with hydrochloric acid at 50 C until reaching a target viscosity of 200-300 BU as measured by Brabender ViscoAmylograph for characterization. The amylose content of all starches decreased slightly after acid modification. Acid primarily attacked the amorphous regions in starch granule and both amylose and amylopectin were hydrolyzed by acid. Acid modification decreased the percentage of chains with degree of polymerization (DP) of 6-12 and increased the percentage of chains with DP 25-56, presuming a result of breakdown of amylose and long chains in amylopectin. The long chains in amylopectin were assumed to link the short-chain clusters and locate in both the crystalline and amorphous regions. Acid-thinned potato starches produced much firmer gels than did acid-thinned corn and rice starches, possibly from its relatively higher percentage of long chains in amylopectin. The short-term gel structure development of acid-thinned starches was more dependent on the amylose content, while the long-term gel formation may be dominant by the long chains in amylopectin.