Effects of preparation temperature on gelation properties and molecular structure of high-amylose maize starch

In this study, 3% aqueous high-amylose maize starch (Hylon VII) dispersions were heated to temperatures of 140-165 degreesC. The onset and rate of gel formation was observed using a small-strain oscillation rheometer as a function of temperature from 90 to 25 degreesC. The gel formation clearly began earlier in high-amylose starch paste preheated at lower temperatures, but the rate of gelation was slower and the resulting gel was weaker in comparison with starch pastes preheated at higher temperatures. In addition, the structure of the final gels was studied using large deformation compression measurements. The most rigid gel structure on the basis of small and large deformation tests was obtained for high-amylose starch gel preheated to 150-152 degreesC, depending on the type of measurement. The rate of gelation was also fastest in that temperature range. High-amylose gels heated to higher temperatures lost their rigidity. The molecular weight distribution of starch molecules was measured by size-exclusion chromatography. Heating caused extensive degradation of amylopectin, which had a great effect on amylose gel formation and the final gel properties of high-amylose maize starch. Micrographs of Hylon VII gels showed that phase separation of starch components visible in light microscopy occurred on heating to higher temperatures.