Effects of the components in rice flour on thermal radical generation under microwave irradiation.

The relationships between radical generation under microwave irradiation and the components of various types of rice flour were investigated. Electron paramagnetic resonance (EPR) spectroscopy was used to characterize the radicals found in rice flour samples. The EPR spectra revealed that several types of radical (carbon-centered, tyrosyl and semiquinone) were localized in the starch and protein fractions of the rice flour. The signal intensity of the free radicals was observed to increase exponentially with increasing microwave power and residence time. The rice bran samples exhibited the greatest free radical signal intensity, followed by the brown rice samples and the white rice samples. This finding was consistent for both the native and the microwaved samples. The ratio of rice starch to rice protein also played an important role in the generation of radicals.