EPR Studies of Thermally Treated Oxidized Corn Starch

The formation of radicals in oxidized corn starch at 20–250°C in air was investigated by quantitative EPR spectroscopy. It was found that the presence of carboxyl groups in the oxidized starch increases the starch's ability to generate radical species. Introducing Cu²⁺ ions into the starch, as a catalyst or as an EPR probe, leads to the formation of copper‐carboxyl complexes containing two carboxyl ligands. Drastic increase in the number of radical species at about 250°C is accompanied by a decrease in the intensity of EPR signal of Cu²⁺‐carboxyl complexes, indicating that the thermal degradation of oxidized corn starch occurs with the formation of radicals, probably via breaking the chemical bonds in the carboxyl groups.