Chapter 8 - Free Radicals in Nonirradiated and Irradiated Foods Investigated by ESR and 9 GHz ESR Imaging

Abstract

This chapter describes our attempts to investigate the locations of stable paramagnetic species and the antioxidant properties in various shiitake mushrooms (Lentinus edodes) and sesame seeds using continuous wave (CW) electron paramagnetic resonance (EPR) and 9GHz EPR imaging. Continuous wave 9GHz EPR detected paramagnetic radical species in various foodstuffs. A peak-to-peak EPR linewidth (ΔHpp) is approximately 0.57mT for fresh and dry mushrooms. The single linewidth of black sesame seeds was narrower than that of irradiated white sesame seeds. A very small signal was detected for white sesame seeds. Two-dimensional (2D) imaging of the sharp line using a 9GHz EPR imager showed that the radical species were located in the cap and shortened-stem parts of the mushroom. No other location of the species was found in the mushroom. However, radical locations and concentrations varied along the cap of the mushroom. For the first time, 9GHz EPR imaging determined the exact location of paramagnetic species in the shiitake mushroom. Distilled water extracts of the pigmented cap surface, as well as the inner cap of the mushroom, showed similar antioxidant activities which reduced an aqueous solution of 0.1mM 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL). The 2D imaging using a 9GHz EPR imager for various sesame seeds showed that the paramagnetic signals in black sesame seeds were located on the seed coat (skin) and in the hilum region. The signal with the highest intensity was obtained from the hilum part. A very low intensity image was observed for the white sesame seeds. In addition, the 2D imaging of the irradiated white sesame seeds showed that free radicals were located throughout the entire seed. Therefore, CW EPR and 9GHz EPR imaging showed the exact location of radical species in various foodstuffs.