The effect of cooling conditions on jet-cooked normal corn starch dispersions

When aqueous dispersions of normal corn starch are jet-cooked under excess steam conditions, the properties of the final product depend on the manner in which the cooked dispersion is cooled. Phase separation of amylose and amylopectin dramatically alters the final properties, and the extent of phase separation depends on the processing history of the sample. The aim of this study was to determine the effects of cooling rate, stirring rate and starch concentration on the rheology and microstructure of the cooled dispersion. A Rapid Visco Analyser was used to obtain a range of cooling profiles and stirring rates. Rheological measurements showed that samples that were stirred during cooling formed stronger gels than unstirred samples. Light microscopy revealed that after cooling, both irregular, amorphous particles and spherical or toroidal crystalline particles were observed in various proportions depending on starch concentration, cooling rate and stirring during cooling.