Influence of prior acid treatment on acetylation of wheat, potato and maize starches

Functional properties of acid-thinned, acetylated, and acid-thinned acetylated wheat, potato, and maize starches were investigated. Total amylose content and the extent of amylose leaching were increased after acid-thinning in all the starches indicating creation of more linear segments. Acid treatment decreased the swelling factor of potato starch at all tested acid concentrations but slightly increased it in wheat and maize starches in low acid treatment. Acid-thinning increased gelatinization temperatures and enthalpy but greatly decreased peak viscosity of all the starches. Wheat and maize starches showed early viscosity increase after acid-thinning but it was delayed in potato starch. Potato starch produced firmer gels after acid-thinning but wheat starch gave weaker gels. For maize starch, gel hardness was increased with low concentration acid treatment. Unchanged melting enthalpy of amylose-lipid complex in acid-thinned starch reflects its resistance to acid hydrolysis. Amylopectin retrogradation of potato and maize starches was not affected by acid modification but it decreased in wheat starch. Acetylation decreased gelatinization temperature and enthalpy, amylopectin retrogradation and gel hardness, but increased swelling factor, amylose leaching and peak viscosity. Acid-thinning decreased the degree of substitution. Introduction of acetyl groups to acid-thinned starches decreased gelatinization and retrogradation transition parameters and produced very soft gels. (c) 2007 Elsevier Ltd. All rights reserved.