Modified starch, no matter what the source, is prepared by treating the starch physically, enzymatically, or chemically, changing the properties of the starch. Gluten ingredients are not used in the process, so if the starch was gluten free to begin with, it is gluten free after it is modified.
Starches are used in food to make them thicker, stable, or to help the ingredients blend together. They are used in pharmaceuticals to make the active ingredients break apart during digestion. Starches are modified to make them work better under certain conditions. Starches may be modified make them more stable when they are heated or cooled or frozen or exposed to acid; to to change their texture; to make a substance thicker or thinner; or to make products gel faster or slower.