Microscopic Evaluation of Hydroxypropyl Potato Starch Granules During Treatment with Urea

A microscopic methodology was devised for the quantitative measurement of the changes in light intensitiy during the loss of birefringence of starch granules in aqueous urea under polarized light. This has been adapted to a native potato starch, hydroxypropyl potato starches of varying molar substitution (M.S.) and a hydroxypropyl and cross-linked potato starch. Several of the factors influencing the measurement results such as urea concentrations, sodium sulphate content and temperature were examined. The hydroxypropyl potato starches rapidly lost their birefringence with increasing M. S., and the relationship between the M. S. and the rate of changes in light intensity was found. There were marked differences in the morphology of the swollen shapes of granules between hydroxypropyl potato starch, and hydroxypropyl cross-linked potato-starch.