ESR investigation of starch gelatinization using novel spin probes.

The spin probes 1,1,3,3-tetramethylisoindolin-2-yloxyl (TMIO) and the sodium salt of its sulfonate, 1,1,3,3-tetramethylisoindolin-2-yloxyl-5-sulfonate (NaTMIOS) were used to monitor the microviscosity changes of water during starch gelatinization. In cereal starch, which contains mainly A-type polymorphs, evidence was found for the amylopectin and amylose regions, the latter undergoing a transition at about 55 degrees C and a large increase in the microviscosity on cooling. Pea starch contains both A-and B-type polymorphs and this was also found to have two domains and the 55 degrees C transition was observed for the amylose phase: the less mobile amylopectin showed a reversible decrease in water microviscosity on heating.