Electron spin resonance studies of free radicals in gamma-irradiated soybean paste

Free radicals in gamma -irradiated soybean paste were investigated by elect ron spin resonance (ESR) spectroscopy to determine the effect of temperatur e (77-296 K) and moisture content (1-54%) of samples irradiated at high dos e (1-40 kGy). The samples were kept in liquid nitrogen (77 K) during irradi ation and subsequent ESR measurements. The spectra shown at 77 K consisted of the hydrogen atom lines at low and high field and complicated symmetric spectrum. By increasing the microwave power, the line shape of ESR spectra altered, which indicated the detection of different paramagnetic centers at different microwave powers. In saturation curves, it was possible to selec t four types of spectra components which were different in their relaxation times. By the different irradiation doses, the change in free radical conc entration showed a curvilinearaly increasing relationship with irradiation dose in wet samples, whereas a proportional relationship was observed with dried samples. This might indicate that the indirect process of free radica l formation was involved with the existence of free water radicals in the w et samples.