The gelation characteristics of natural potato starch and two modified starches have been compared with their water sorption isotherms determined at 25°C. The pregelatinized starch gels more readily than the natural starch, but has a lower water sorption capacity below 90% relative humidity.The cross-linked starch gels less readily than the natural starch on heating but has a similar water sorption isotherm.

A dye staining method has been used to determine the proportion of starch granules which are damaged as a function of initial water ctontent during (a) microwave heating and (b) baking in a forced-air-convection oven.Although the granules are damaged much more rapidly on microwave heating, it was found that the proportion of damaged granules depends on the amount of water in the sample rather than on the method of heating. Samples of potato starch containing up to 30% water suffer no measurable damage.Beyond this point, damage increases with increasing moisture content, and all the granules are damaged provided the samples contain initially 55% or more water.