ESR Studies of Transient Free Radicals in Irradiated Food Components

Electron spin resonance (ESR) detection techniques are applied to the study of free radicals produced in model systems representing food components irradiated at subfreezing temperatures. The modifications made to a 10 MeV linear electron accelerator (LINAC) and a 9.5 GHz ESR spectrometer in order to achieve an in situ irradiation/ detection capability are described. The combined LINAC-ESR system has the capability of delivering a 2-5 kGy pulse of electrons through axial holes in the poles of the ESR magnet and into the center of a special microwave resonator of the remotely operable ESR spectrometer. Innovative interfacing hardware and software for faciliating data acquisition, digitization, transfer, and processing combined with appropriate trigger sequencing controls permit a wide range of fast scan ESR experiments to be conducted. Spectra that are 150 gauss wide can be swept in 9 ms at variable times following a single pulse of electrons. Radicals having lifetimes in the tens of milliseconds can be studied in low temperature systems from 145 to 260 K. Methods used to prepare samples for such studies and to control their temperature are described. Examples illustrating the capabilities of this kinetic ESR system are drawn from current work on the model system N-acetylalanine, in which interconversions of radicals can be monitored. Comparison is made between results from this model system and what has been observed in the myofibrillar protein myosin.