Electron spin resonance spectroscopy identifies radiation-induced markers in 7 kGy-irradiated dried lavers subjected to alkaline pretreatment

Food irradiation was allowed for dried seaweeds for improving microbial quality in Korea and reliable detection methods are required for the routine control in international trade. In this study, three kinds of popular dried laver (seaweeds) were electron-beam irradiated at approved 7 kGy dose, and the radiation-induced signals were detected using electron paramagnetic resonance (ESR) spectroscopy coupled with alkaline pretreatment. The influence of conventional post-irradiation sample pretreatment such as freeze drying (FD) was also compared with that of alkaline pretreatments, i.e., NaOH extraction (NE) and KOH extraction (KE). Non-irradiated samples were characterized by their ESR spectra, having singlet g-values of g = 2.006, 7 kGy-irradiated samples with FD and KE pretreatments did not exhibit any detectable irradiation-induced signals. However, all the irradiated samples treated with NaOH showed a new radiation-induced ESR signal hfcc (hyperfine coupling constant) of 2.3 mT that is different from that of the established cellulose radicals (hfcc of 3 mT). Thus, attempts have been made to understand the origin of the new signal. The improved approach of combination treatment with NaOH and ESR spectroscopy was successful in identifying irradiated dried laver.