Optimizing the conditions for starch dry phosphorylation with sodium mono- and dihydrogen orthophosphate under heat and vacuum

Starch was phosphorylated by reaction with mono- and disodium hydrogen orthophosphate under dry conditions in a vacuum oven at 150-180 degrees C (800 mbar). Studying the different factors affecting the reaction showed that the optimal conditions for starch phosphorylation in the monoester form were: 3 h reaction time, 160 degrees C reaction temperature and pH 6. The different types of starch gave different degrees of substitution; and amylose bound a higher amount of phosphate than amylopectin under similar reaction conditions. Both ash content and acidity of the phosphorylated starch products increased proportionally with the increase in the degree of substitution while the pH of the different modified starch products was nearly in the same range (pH 6.55-6.75).