Formation of Stable Free Radicals in Saccharides by Heating or by UV Irradiation

The formation of stable free radicals was observed by means of ESR spectroscopy not only on heating but also on UV irradiation of powdered saccharides at room temperature in air. Among saccharides used here, the number of free radicals was largest in the powdered disaccharides. On the other hand, free radicals of glucose were obtained by UV irradiation, but not by heating. The number of free radicals was found to increase initially after heating or after irradiation, and then became almost constant. This constant value of the number of free radicals was found to increase with increase of the heating temperature or heating time, or with increase in the duration of irradiation. The ESR spectra of saccharides were not affected by oxygen, but were found to change gradually under conditions of high humidity. Moreover, a hysteresis effect was observed between the number of free radicals and the water content in UV-irradiated potato starch. Free radicals were found to be stable when suspended in benzene, but they were destroyed by kneading the saccharides in water or alcohols.